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Optical properties of cesium bismuth germanate Cs 2 Bi 2 O(Ge 2 O 7) (CBGO) nonlinear single crystal doped with trivalent europium (Eu3+) ions grown from melt were investigated. Strong Eu3+ emission lines in the orange-red range centered at 576, 596, and 617 nm originating from the 5D 0 to 7F 0,1,2 transitions, respectively, were observed. Judd-Ofelt intensity parameters describing f-f transitions were calculated from the room temperature emission and excitation spectra and were used to determine spectroscopic parameters such as radiative lifetimes, transition probabilities and branching ratios3 for 5D 0 level of Eu3+. The values obtained by using Judd-Ofelt approach were compared with experimental results for the 5D 0 excited state. The measurement of the 5D 0 fluorescence decay of Eu3+ ions in the Cs 2 Bi 2 O(Ge 2 O 7) matrix (0.5 at.% in the alloy) confirmed its exponential nature, with a time constant of 0.82 ms at 300 K. The high-resolution laser spectroscopy of CBGO Eu3+ performed at 10 K confirmed the Eu3+ distribution into two distinct sites. Based on both the results of optical spectroscopy and structural analysis, the allocation of sites for Eu3+ ions was discussed. • Cs 2 Bi 2 O(Ge 2 O 7):Eu3+ crystals have been grown from stoichiometric melts under conditions of low temperature gradient. • Judd-Ofelt intensity parameters for f-f transitions in CGBO:Eu3+ have been determined. • The Eu3+ distribution into two distinct sites in CBGO host has been experimentally confirmed. • The values of transition probability and radiative lifetime of the 5D 0 level of Eu3+ in CBGO crystal have been determined. [ABSTRACT FROM AUTHOR]

Photoluminescence characteristics of Gd 2 O 3 :Bi are studied in the 4.2–800 K temperature range by the time-resolved spectroscopy methods. Purely cubic structure of Gd 2 O 3 :Bi is confirmed by XRD. The luminescence of Bi3+(S 6) and Bi3+(C 2) centers is found to arise from the electron transitions from the emitting level of the triplet excited state of Bi3+, corresponding to the 3P 1 → 1S 0 transitions of the free Bi3+ ion. Relaxation processes in the triplet excited state of Bi3+ ions do not result in the population of the lowest-energy metastable level. The absence of the radiative transitions, corresponding to the 3P 0 → 1S 0 transitions of the free Bi3+ ion, explains the short (0.3–2.0 μs) decay time of the triplet emission of Bi3+ even at 4.2 K. The conclusion is made that the fast luminescence decay cannot be caused by the mixing of the metastable and emitting levels of the triplet excited state of Bi3+ by the magnetic field created at the Bi3+ site by the magnetically ordered Gd3+ sublattice. The electron transfer and recombination processes, resulting in the appearance of the photo- and thermally stimulated electron recombination luminescence of Bi3+(S 6) and Bi3+(C 2) centers under excitation in the E exc > 4.3 eV energy region, are also discussed. The energy level positions of the Bi3+(S 6) and Bi3+(C 2) centers in the band gap of Gd 2 O 3 are estimated. [Display omitted] • Photo- and thermoluminescence and XRD are studied for Gd 2 O 3 :Bi3+ powder. • Luminescence arises only from the 3P 1.→ 1S 0 transitions of Bi3+(S 6) and Bi3+(C 2) • This explains a short (∼10−6 s) decay time of the triplet luminescence at 4.2 K. • Fast decay cannot be caused by the magnetic field created at Bi3+ site by Gd3+ sublattice. • Electron transfer processes take place under excitation of Bi3+ with E exc >4.3 eV. [ABSTRACT FROM AUTHOR]

Oxyfluoride glass-ceramics have become a focal point of recent research, positioned to advance significantly in areas such as LED illumination and optical data storage, etc. This study successfully prepared Pr3+-doped fluorosilicate glass and glass-ceramics embedded Na 5 Y 9 F 32 nanocrystals. The introduction of Pr 2 O 3 into the glass matrix disturbs the network structure, leading to a reduction in the band gap from 3.66 eV to 3.42 eV. When subjected to 443 nm light excitation, the 1.0 mol% Pr3+-doped glass-ceramics crystallized at 690 °C for 1.0 h exhibit the most potent luminescence, displaying seven emission peaks resulting from the radiative transition of Pr3+ ions, manifesting yellowish-pink hues. Furthermore, when stimulated by a 450 nm LD, the glass-ceramics display a distinct emission peak at approximately ∼247 nm, attributed to the electron transitions of 4 f 5 d → 3H 4 for Pr3+ ions. The luminescent properties of these glass-ceramics embedded with Na 5 Y 9 F 32 nanocrystals illustrate potential applications in up-conversion and down-conversion luminescence. • A novel Pr3+ doped SiO 2 –Al 2 O 3 –Na 2 O-NaF-YF 3 glass-ceramics was successfully prepared. • Glass-ceramics containing Na 5 Y 9 F 32 crystals exhibit efficient excitation under blue light. • The glass-ceramics exhibit yellowish-pink hues excited by 443 nm light. • The glass-ceramics presents impressive emission peaks at ∼247 nm excited by 450 nm LD. • The work stresses glass-ceramics' huge potential in up-/down-conversion luminescence. [ABSTRACT FROM AUTHOR]

We investigated temperature dependencies of the temporal behaviors of luminescence bands attributed to the radiative transitions from adiabatic potential energy surfaces (APESs) of 1T 1g , 3T 2u +3E u , 3T 1g , and 3A 1u of Tl+ and Au − centers in NaCl crystals. In addition to NaCl:Au − , a luminescence band with the sharp zero-phonon luminescence line was observed in NaCl:Tl+, a strong electron-lattice interaction system. A time-resolved study revealed that this luminescence band with the zero-phonon line in NaCl:Tl + exhibited the decay time of 4.3 ms at low temperatures attributed to the radiative transition from 3A 1u APES. The characteristic temperature dependences of the decay time constant and luminescence intensity of the luminescence from the 3T 1g and 3A 1u APESs were discussed based on a configuration coordinate scheme. The intensities and decay time constants of luminescence bands caused by radiative transitions from the 1T 1g , 3T 2u +3E u , 3T 1g , and 3A 1u APESs changed with temperature through thermally activated nonradiative transitions among APESs. The temperature dependencies of luminescence intensities and decay time constants were analyzed using rate equations that comprise radiative and nonradiative transitions from APESs and among APESs, respectively. The activation energies of APESs were estimated from the best-fit results. The characteristics of thermally activated processes among APESs are revealed in weak and strong electron-lattice interaction systems. • Optical spectra for NaCl:Tl+ and NaCl:Au− were studied with high-resolution. • A zero-phonon line is observed in NaCl:Tl+ of a strong electron-lattice interaction system. • Luminescence properties cannot be explained by a phenomenological three-level model. • Relaxation processes among adiabatic potential energy surfaces were revealed. [ABSTRACT FROM AUTHOR]

Terahertz (THz) luminescence in doped nanostructures with GaAs/AlGaAs quantum wells is studied under conditions of interband optical pumping. The study is carried out on compensated quantum wells with different doping profiles. In one structure, compensation is carried out directly in each quantum well by introducing donors and acceptors with the same concentration. In the other, donors and compensating acceptors are spatially separated, namely, donors are located in quantum wells, while acceptors are located in barriers. The spectra of THz photoluminescence are studied at various temperatures and levels of optical excitation. It is shown that the main contributions to the THz emission in both structures are due to the electron transitions from the first electron subband and excited donor states to the ground donor states. It is found that the spatial separation of donors and acceptors provides an approximately twofold increase in the integrated intensity of THz emission. This is directly related to the increase in the rate of dynamic depopulation of the ground donor levels due to the optical transitions from the ground donor states to the first heavy-hole subband, which is confirmed by photoluminescence studies in the near-infrared spectral range. [Display omitted] • Spatial separation of donors and acceptors provides an enhancement in THz emission. • THz emission is due to radiative electron transitions to the ground donor states. • Higher rate of ground donor level depopulation leads to enhancement in THz emission. [ABSTRACT FROM AUTHOR]

Luminescence properties of undoped Li 6 Y(BO 3) 3 (LYB) crystals grown by the Bridgman method as well as undoped and praseodymium doped LYB crystals grown by the Czochralski method were studied under excitation by ultraviolet light, synchrotron radiation and electron beam in the temperature region of 5–300 K. The emission bands peaking at 4.8, 3.76 and 2.95 eV were found in undoped Czochralski-grown crystals, while the band at 3.34 eV was dominant in the Bridgman-grown crystals. These bands are presumably ascribed to excitons localized at regular and defect-perturbed lattice sites. Intense emission bands peaking at 4.75, 4.50, 4.17 and 3.98 eV were discovered in Pr doped crystals at low temperatures and related to the interconfigurational 4f15d1 → 4f2 radiative transitions in Pr3+ ions. The structure of the emission spectrum is shown to be determined by the 3H 4 , 3H 5 , 3H 6 , 3F 2 , 3F 3 , 3F 4 terms of the Pr3+ ion. The characteristic decay time of the 4f15d1 → 4f2 emission is τ = 24 ns at low temperatures, however, it shortens to 9 ns by room temperature due to a strong thermal quenching. The study of glow curves and spectra of thermostimulated luminescence in Li 6 Y(BO 3) 3 :Pr crystal irradiated by 10-keV electron beam shows that Pr3+ ions do not participate in an electron-hole recombination process. • High quality undoped and Pr doped Li 6 Y(BO 3) 3 were spectroscopically studied • Interconfigurational Pr3+5d-4f luminescence is revealed at low temperatures • Fast Pr3+ 5d-4f luminescence is quenched at room temperature • Pr3+ do not participate in the electron –hole recombination processes [ABSTRACT FROM AUTHOR]

This article presents a description of the structural-optical relationship in amorphous borate glass, with a decent investigation of Judd-Ofelt parameters to understand the effect of structural changes on optical properties due to the erbium oxide addition. Using density measurements, the effect of heavy molecular weight and larger ionic radius of erbium oxide was demonstrated. FT-IR analysis revealed the BO 3 to BO 4 conversion, confirming the network polymerization and connectivity. Astonishingly, the effect of erbium oxide on the increased band gap energy and the mitigated Urbach energy was demonstrated. Interestingly, Judd-Ofelt analysis was utilized to demonstrate the impact of the composition changes on the relation between the structural changes and optical properties. The influence of excited configurations of E r 3 + ions was measured from the line strengths. The hypersensitive transitions from I 15 / 2 4 t o H 11 / 2 4 and G 9 / 2 4 were observed at 375 nm and 519 nm, which have relatively higher intensities compared to other ones. Thus, they are attractive transitions for light emitting devices, LEDs, and solid lasers. The decreased values of Ω 2 parameter is related to the increase in symmetry and high polarization around E r 3 + ions. Consequently, the decrement in Ω 2 suggests that the bond nature between E r 3 + and O 2 − ions tends to be more ionic. Calculations of radiative parameters such as spontaneous radiative transition probability, radiative lifetime, and branching ratio were presented. The hypersensitive transitions have the highest values of the spontaneous radiative transition probability, predicting their high luminescence efficiency in glass host, besides the effectiveness of their usability in designing photonic devices. The obtained high branching ratio confirmed the lasing action of E r 3 + ions in the glass host, especially the hypersensitive transitions of E r 3 + ions. • Alkali borate glasses doped erbium oxide were prepared. • The structure-property relationship was described by different techniques. • Judd-Ofelt intensity parameters confirmed the ionic nature of E r 3 + with ligands. • Wide band gap and related parameters confirm the usability of samples in optics realm. • Hypersensitive transitions have the highest values of radiative parameters. [ABSTRACT FROM AUTHOR]

Lu 2(1- x) Pr 2 x O 3 nanoscintillators (x = 0.0005, 0.001, 0.0015, 0.003, 0.005) with excellent red emission and a response time of 185.7 μs were synthesized by a coprecipitation method. It is found that both photoluminescence and radioluminescence intensities show an initial rising and then decreasing trend with increasing Pr3+ concentration and the strongest intensity can be obtained at x = 0.001. By determining the average distance between Pr and O, the radiative transition processes from 3P 0 and 1D 2 to 3H 4 and nonradiative transition process from 3P 0 to 1D 2 can be confirmed. Meanwhile, the afterglow level of Lu 2 O 3 :Pr3+ nanoscintillators with an average size of 112.3 nm was found to be 2190 ppm. Based on the spectral data and density functional theory calculations, the afterglow can be related to Pr L u · traps due to the presence of Pr4+ in Lu 2 O 3 :Pr. When Sm3+ ions were doped into Lu 2 O 3 :Pr3+, it is found that it leads to the decreased creation of Pr4+, the reduced afterglow level and the improved radioluminescence. By means of Lu 2 O 3 :Pr3+, Sm3+ nanoparticles being dispersed into polymethyl methacrylate (PMMA) polymer, PMMA-Lu 2 O 3 :Pr3+, Sm3+ composite films with fast response time and radiation resistance were prepared by a rotating coating method. The static X-ray imaging with a spatial resolution of 5.5 lp/mm using the composite film as an imaging screen was realized at extremely low safe dose of 4.6 μ G y. Meanwhile, for the broken electric wire used as an object, the clear X-ray image can be observed. Our results suggest that Lu 2 O 3 :Pr3+, Sm3+ nanoscintillators have potential applications in medical imaging and nondestructive testing. • Sm3+ and Pr3+ codoped Lu 2 O 3 nanoscintillators were synthesized by coprecipitation method. • Sm3+ doping improves the radioluminescence intensity of Pr singly doped sample by 1.8 times. • Sm3+ doping reduces the afterglow level of the Lu 2 O 3 :Pr samples by decreasing the presence of Pr4+. • Lu 2 O 3 :Pr3+,Sm3+ nanoscintillators can be potentially used as imaging screens in X-ray imaging. [ABSTRACT FROM AUTHOR]

Borotellurite and fluoroborotellurite glasses doped with Sm3+ ions were synthesized and studied their physical, photoluminescence, x-ray induced luminescence, and fluorescence decays. The glasses that were prepared by melt quenching technique were labelled by BTZOS for 30B 2 O 3 ​+ ​29TeO 2 ​+ ​30BaO ​+ ​10ZnO ​+ ​1Sm 2 O 3 and BTZFS for 30B 2 O 3 ​+ ​29TeO 2 ​+ ​30BaO ​+ ​10ZnF 2 ​+ ​1Sm 2 O 3. The glass becomes more transparent when ZnO was replaced by ZnF 2. It was found that the replacement of ZnO by ZnF 2 increases absorbance and luminescence of Sm3+ ions. The Judd - Ofelt intensity parameters were evaluated from measured absorption spectra for BTZOS and BTZFS glasses and their trend is found to be Ω 2 > Ω 4 > Ω 6. The sharp and intense emission peak was originated from 4G 5/2 → 6H 7/2 transition centred at 600 nm under 403 nm excitation. The colour coordinates of BTZOS and BTZFS glasses are found to fall in the orange region with CCT <4000 K, suitable for solid-state lighting. BTZFS glass exhibits better radiative properties such as long lifetime, higher quantum efficiency (η), radiative transition probability (A R), stimulated emission cross-sections (σ e), branching ratios (β), gain bandwidth and figure of merit, lower non-radiative decay rate (W CR) and saturation intensity (I s) than BTZOS glass. From the analysis of the results, it is concluded that BTZFS glass could be more suitable for a gain medium for lasers in the visible region. [ABSTRACT FROM AUTHOR]

A set of ZnMoO 4 polycrystalline samples was synthesized by solid state reaction method and characterized by XRD structural analysis, ICP elemental analysis, SEM-EDX analysis, UV–Vis diffuse reflectance spectroscopy. The photoluminescence (PL) properties of ZnMoO 4 samples were studied in 8–300 K temperature range with use of synchrotron radiation as an excitation source. The geometry-optimized electronic structure calculations of perfect and defective ZnMoO 4 crystals were carried out by the DFT-based band-structure methods, plane-wave pseudo-potential (CASTEP program package) and FP-LAPW (Wien2k package). A number of point defects which can influence the luminescence properties of ZnMoO 4 was considered in calculations, namely the oxygen vacancy V o , compensated vacancies V o + V Zn , tungsten impurity W Mo and the MoO 3 -deficient phase Zn 3 Mo 2 O 9. Comparative analysis of experimental data and calculation results allowed explanation of the origin of the red and blue-green luminescence emission bands of ZnMoO 4 as well as formation of their excitation spectra. It is assumed that the green component of ZnMoO 4 luminescence emission, like in other molybdates of MIIMoO 4 family (MII = Ca, Sr, Cd, Pb) originates from radiative annihilation of excitons self-trapped on regular MoO 4 groups. The Red component of ZnMoO 4 emission has a defect-related origin and it originates from radiative transitions in MoO 4 groups located near oxygen vacancies. [ABSTRACT FROM AUTHOR]

A series of trivalent samarium doped lanthanum molybdate nanophosphors were prepared by co-precipitation route. The formation of highly crystalline tetragonal nanocrystals with space group I41/a is identified from powder X-ray diffractogram. The morphology and the oriented attachment mediated growth mechanism of the nanocrystals were recognized from TEM analysis. The strong and broad charge transfer band in the near ultra violet region favours excellent excitation of the nanophosphors and the energy transfer from host matrix to Sm3+ ions is established on account of the characteristic emissions of trivalent samarium ions upon host sensitization. The Judd-Ofelt (JO) theoretical analysis was carried out to have an insight into the spectroscopic characteristics of La 2-x Sm x (MoO 4) 3 nanophosphors. The relatively higher value of Ω 2 predicts more asymmetric environment of Sm3+ sites in the host lattice, favouring the dominance of electric dipole transitions and the various radiative parameters are evaluated. In spite of the excitation channel, the 4G 5/2 → 6H 9/2 transition of Sm3+ observed at 645 nm is the most prominent emission transition. The maximum emission intensity is observed for La 1.98 Sm 0.02 (MoO 4) 3 nanophosphors and as the doping concentration exceeds this limit, there will be fall in emission intensity due to concentration quenching effect. A detailed investigation on the decay behaviour of host sensitized and direct excited emission of samarium ions was conducted and the average lifetime values are calculated. The CIE chromaticity co-ordinates calculated for different excitation routes fall in the reddish orange region of CIE diagram and the same for La 1.98 Sm 0.02 (MoO 4) 3 nanophosphors are found to be (0.601, 0.394) with a colour purity of 97.21% which disclosed the relevance of La 2−x Sm x (MoO 4) 3 as a potential red phosphor material. Image 1 [ABSTRACT FROM AUTHOR]

Series of silica-based glasses doped with antimony was synthesized to host luminescent silver clusters formed via Na+-Ag+ low-temperature ion exchange and heat treatment. Spectroscopic study reveals that increase in antimony concentration affects emission spectra, quantum yields, and fluorescence lifetimes. Photophysical processes rate constants, including radiative and nonradiative transitions and intersystem crossing, were estimated based on experimental spectroscopic characterization. Correlation between photophysical processes rate constants and increase in concentration of antimony was demonstrated. • Silica-based glass series was synthesized to host luminescent silver clusters. • Spectroscopic characterization of silver clusters emission was performed. • Rate constants of cluster photophysical processes were evaluated based on time-resolved and steady-state spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract Improving the infrared-band luminescent property of rare-earth doped materials is a challenging task. In this work, the enhanced 2.0 µm band emission study in Ho3+/ Yb3+/Er3+ tri-doped tellurite glasses with composition TeO 2 -ZnO-WO 3 -La 2 O 3 was given. The tellurite glasses were prepared by conventional melt-quenching technique and characterized by absorption spectrum, emission spectrum, fluorescence decay curve, differential scanning calorimeter (DSC) curve, X-ray diffraction (XRD) pattern and Raman spectrum. The DSC curve displays the good thermal stability with glass transition temperature larger than 420 °C, the XRD pattern reveals the amorphous state nature and Raman spectrum clarifies the vibrational units of glass network. Based on the absorption spectrum, important spectroscopic parameters like spontaneous radiative transition probability, radiative lifetime, absorption and emission cross-sections, and gain coefficient are determined to predict the potential luminescent properties in near-infrared band, while the fluorescence spectrum demonstrates the enhanced 2.0 µm band emission of Ho3+:5I 7 → 5I 8 radiative transition aroused by Er3+ introduction. Compared with the Ho3+/Yb3+ co-doped sample, an enhancement of about 93% in 2.0 µm band emission intensity is appeared in the tri-doped tellurite glass after introducing 0.8 mol% amount of Er 2 O 3 under the excitation of 980 nm. The enhanced 2.0 µm band emission is attributed to the energy transfers among Yb3+, Er3+ and Ho3+ ions, and fluorescence decay curves together with the energy transfer mechanism are analyzed to elucidate the observed luminescent enhanced phenomena. The results indicate that Ho3+/Yb3+/Er3+ tri-doped tellurite glass possesses excellent 2.0 µm band luminescent property and can be an attractive candidate for solid-state lasers. [ABSTRACT FROM AUTHOR]

Abstract High-brightness, red-emitting Ca 9 Gd 1− x (PO 4) 7 : x Eu3+ phosphors were developed via the facile route of solution-combustion. The Rietveld-assisted structural analysis of Ca 9 Gd(PO 4) 7 and Ca 9 Gd 0.40 Eu 0.60 (PO 4) 7 systems unveiled a trigonal crystal system having R3c (161) space-group symmetry. The absence of JCPDS data was compensated by simulating one from refined structural prototype. The band-gap for the host and best luminescent composition were determined to be 4.55 and 4.01 eV, respectively. The ratio of Judd-Ofelt parameters inferred a very high asymmetry around activator ion which can further be enhanced as a function of dopant concentration. The refractive index of Ca 9 Gd(PO 4) 7 was determined to be 2.34. The value of stimulated emission cross section, total radiative transition rate and non-radiative transition rate for Ca 9 Gd 0.40 Eu 0.60 (PO 4) 7 are calculated from detailed photo-luminescent (PL) analysis. Furthermore, very high value of quantum efficiency (98.13%) and radiative lifetime (1.85 ms) suggested that Ca 9 Gd 0.40 Eu 0.60 (PO 4) 7 nanophosphor have practical applicability in PC-WLEDs (components of solid-state lighting). Graphical abstract fx1 [ABSTRACT FROM AUTHOR]

Abstract Dy3+-doped glasses with compositions of (69- x)B 2 O 3 + 10TeO 2 + 10Al 2 O 3 + 10Li 2 O + x Dy 2 O 3 (x = 0.1; 0.5; 1.0 and 2.0 mol%) were prepared by a melt–quenching technique. An in-depth Judd-Ofelt analysis has been carried out to estimate the influence of the hypersensitive transitions (HST) of Dy3+on the validity of the obtained intensity parameters Ω λ (λ = 2, 4, 6). The thermalization effect of the three-levels system of 6H 13/2 (level 0), 4F 9/2 (level 1) and 4I 15/2 (level 2) was taken into account to evaluate its radiative transition probabilities, life times and energy levels. The obtained results were compared with the experimental data to estimate the validity of the Judd-Ofelt analysis. The Inokuti-Hirayama model was used to analyze the luminescence decay curves. The dipole-dipole interaction was shown to be the dominant mechanism in energy transfer process through cross-relaxation between Dy3+ ions. The possibility to produce the light with chromaticity coordinates in the white-light region by mixing intense blue (484 nm, 4F 9/2 → 6H 15/2) and yellow (575 nm, 4F 9/2 → 6H 13/2) emissions of the single Dy3+doped alumino-lithium-telluroborate glass was observed and estimated. [ABSTRACT FROM AUTHOR]

Abstract This contribution reports on detailed experimental and numerical investigations of both near-infrared (NIR) and mid-infrared (MIR) photoluminescence obtained in praseodymium trivalent ion doped chalcogenide-selenide glass fiber. The experimental analysis allows for the identification of the radiative transitions within the praseodymium ion energy level structure to account for the photoluminescent behavior. Numerical analysis is carried out using the rate equations' approach to calculate the level populations. The numerical analysis provides further insight into the nature of the radiative transitions in the Pr3+ ion doped chalcogenide-selenide glass and allows for the identification of the electronic transitions, which contribute to the observed photoluminescence. The numerical results agree well with the experimental results. [ABSTRACT FROM AUTHOR]

Abstract The present study deals with synthesis, characterization and analysis of dysprosium doped NaCl−BaO−Bi 2 O 3 −B 2 O 3 glass samples so as to evaluate its feasibility in solid state lighting applications. Various analytical investigations viz. X-ray diffraction (XRD), density, molar volume measurement, Fourier Transfer Infrared (FTIR) Spectroscopy, UV–Vis–NIR and photoluminescence (PL) has been carried out to study the impact of replacing BaO by NaCl content on white light emission parameters in the host glass matrix. The glassy nature of the prepared samples was confirmed through peak free X-ray diffraction profiles. FTIR spectroscopy reveals the network modifier role of NaCl as four coordinated boron are converted into three coordinated ones. Six absorption peaks from 6H 15/2 ground state to 4I 15/2 , 6F 5/2 , 6F 7/2 , 6F 9/2 , 6H 9/2 , 6H 11/2 excited states were observed from UV–Vis–NIR spectra of all glass samples. The fundamental absorption edge, optical band gap and Urbach energy were calculated and reported in the present study. Excitation spectra recorded at 578 nm provide six excitation peaks at 349, 363, 386, 425, 452, 471 nm. The highly intense peak at 452 nm was further selected to record the emission spectra and four prominent peaks centred at 484 nm (blue), 578 nm (yellow), 668 nm (red) and 755 nm due to various 4F 9/2 →6H J (J= 9/2, 11/2, 13/2, 15/2) radiative transitions in visible and near infrared region of the spectra were observed. From emission spectra various parameters viz. Y/B ratio, (x,y) chromaticity coordinates, and correlated color temperature (CCT) were determined. The Y/B ratio for all the glass samples was found to be greater than 1 signifying a covalent bonding between Dy3+ and O2- ions. The obtained (x,y) coordinates shows a balanced white emission (0.36, 0.39) which is quite stable with varying compositions. The value of CCT for present glass system was found to lie between 4339–4537 K which is a characteristic of near the white light region marking the suitability of synthesized glasses as an alternative materials for solid state lightening applications. [ABSTRACT FROM AUTHOR]

Abstract Er3+/Yb3+ co-doped glass ceramic samples were prepared by melt-quenching method utilizing nominal composition 52SiO 2 –8Na 2 CO 3 –16Al 2 O 3 –33NaF-3LuF 3 -0.15Yb 2 O 3 − 0.03Er 2 O 3 (in mol%). The spectral characteristic was studied based on Judd-Ofelt theory. Spectrum intensity parameters Ω λ (λ = 2,4,6) were calculated on the basis of the absorption spectrum. The theoretical and experimental oscillator strengths were calculated according to the spectrum intensitty parameters, and the root mean square deviation (δ rms) of glass ceramic sample was 4.28 × 10−6. The parameters such as transition probability, decay branching ratios and level lifetime of Er3+ were obtained. Lifetimes of metastable level 4I 13/2 and 4I 11/2 in as-prepared samples are respectively 11.64 and 13.61 ms which are suitable for up-conversion intermediate levels. Decay branching ratio of 4I 13/2→ 4I 15/2 is nearly 100% in Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples which can be used to produce 1543 nm laser. Under the excitation of 980 nm diode laser, up-conversion luminescence is observed at the wavelength of 549 nm and (653, 664) nm, corresponding to the radiative transitions of Er3+:4S 3/2 → 4I 15/2 and 4F 9/2 → 4I 15/2 , respectively. The numbers of absorbed photons in the transition process of Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples are estimated at 1.99 and 2.06 respectively according to the relationship between the up-conversion transmitting power and the 980 nm LD laser power. It is determined that the transition process of Er3+/Yb3+ co-doped oxyfluoride glass ceramic samples is two-photon absorption process. [ABSTRACT FROM AUTHOR]

Abstract We investigated thermal and fluorescence properties of Er3+ doped fluoroaluminate multi-component glasses modified by TeO 2 and CaCl 2. A better thermal stability with a higher Δ T (98 °C) was obtained for the TeO 2 modified sample, which had a high radiative transition probability (A rad) of the Er3+: 4I 11/2 →4I 13/2 transition. In addition, under 980 or 808 nm excitation, the Er3+ 2.7 µm emission intensity of the TeO 2 modified sample decreased owing to its increased hydroxyl content induced by TeO 2 modifiers. Excellent mid-infrared fluorescence along with a longer lifetime (3.48 ms) were observed in the glass tuned by CaCl 2. The CaCl 2 modified sample exhibited higher stimulated absorption and emission cross sections, obtained using the Füchtbauer-Ladenburg and McCumber formulas. Moreover, the strong effect of hydroxyl on the mid-infrared fluorescence properties was systematically analyzed. The oxygen network modifiers in the fluoroaluminate multi-component glass provide improved thermal properties, while the AlF 3 -based glasses with chlorine network modifiers have larger potentials for applications in the mid-infrared region. [ABSTRACT FROM AUTHOR]

The influence of temperature on the near-infrared emission band corresponding to the radiative relaxation from 4 I 13/2 to 4 I 15/2 electronic states of Er 3+ was investigated in Y 2 O 3 powder prepared by combustion synthesis. We observed that the electronic population distribution among various Stark levels of 4 I 13/2 and 4 I 15/2 changes with temperature in a way that is favorable for temperature sensing based on the luminescence intensity ratio technique. We also observed that the absolute temperature sensitivity varies by around 300% depending on the Stark transitions of choice with the highest relative temperature sensitivity value being around 2 × 10 −3 K −1 at room temperature. Optically induced heat was found to be negligible under our experimental conditions. [ABSTRACT FROM AUTHOR]

YAlO 3 crystals doped with different concentrations (0.05, 0.1, 1.0 at.%) of Pr3+ ions were studied in this work. The crystals were grown from the melt by a micro-pulling-down (MPD) method. Luminescence and energy-storage properties of YAlO 3 :Pr crystals were studied using cathodoluminescence (CL), as well as thermoluminescence (TL) and optically stimulated luminescence (OSL). Instead of a conventional optical illumination with blue LEDs, infrared light was used for optical stimulation (IRSL). For the YAlO 3 :Pr crystals both TL glow-curves and IRSL decay curves were extensively analyzed. Both d-f transitions in UV range and f-f transitions in the visible range of Pr3+ ions were observed including radiative transitions from 3P j (j = 0,1,2) to 3F 2,3,4 and 3H 4,5,6 levels. The highest CL signal was measured for the lowest Pr3+ concentration of 0.05 mol% and a strong luminescence quenching was observed for the increase in the Pr3+ content. For the increasing dose of radiation, the intensity of the main TSL glow-peak at around 170–200 °C shows a linear behavior, regardless of the applied dopant concentration. Due to the highest TL and IRSL radio-sensitivity and stability in time after the irradiation, the YAlO 3 :Pr (0.05 mol%) perovskite seems most promising material for radiation measurement applications. • YALO 3 crystals made by micro-pulling-down technique have been investigated. • The crystals were doped with Pr3+ Rare-Earths ions. • Luminescence of Pr3+dopants was clearly observed. • Good embedded of Pr3+ions in YALO 3 matrix was confirmed. • YALO 3 with Pr3+ (0.05 mol%) was found to present the best dosimetric properties. [ABSTRACT FROM AUTHOR]

Tetragonal Tm3+:YPO 4 single crystals were successfully grown by high temperature solution method. The crystal growth, structures and detailed spectroscopic properties including polarized absorption spectra, FT-IR and Raman spectra, polarized fluorescence spectra and lifetime were reported for the first time. The bandwidth of absorption band around 800 nm were determined to be 13.1 nm for π-polarization and 22.5 nm for σ-polarization, indicating that Tm3+:YPO 4 crystal is suitable for commercial AlGaAs laser diodes pumping. Spectroscopic parameters, including J-O intensity, oscillator strength, line strength, fluorescence branching ratios, spontaneous transition rates and radiative lifetime were analysed by J-O theory. The continuous positive gain range can reach 270 nm when the excited state ion fraction β ≥ 0.5, showing the promising applications in tunable and ultrafast laser. The results indicate that Tm3+:YPO 4 crystal is a potential laser medium which is expected to realize at around 1.9 μm. [Display omitted] • The Tm3+:YPO 4 crystals were grown successfully from Pb 2 P 2 O 7 solution. • Spectral parameters of Tm3+ ions were calculated in detail based on J-O theory. • Obvious broadband emission characteristics can be observed at around 1.9 μm. [ABSTRACT FROM AUTHOR]

We present a spectroscopic study of defects in fused silica (SiO 2) samples, showing their signatures in photoluminescence (PL) excitation and emission spectra, PL decay rate, and Fourier-transform infrared and Raman spectra. Using the multi-transition Franck-Condon (FC) analysis, we were able to characterize phonon coupling with oxygen-deficient centres (ODC) in fused silica. Four observed FC emission bands, located at 2.8, 3.2, 4.2, and 4.4 eV were identified as singlet-singlet and singlet-triplet transitions in two different types of ODC defect. This model was confirmed by PL decay data and allowed us to describe different emission pathways of ODC defects. • A spectroscopic study of the defects in fused silica (SiO2) has been investigated, by measuring photoluminescence excitation and emission spectra, PL decay rate, and Fourier-transform infrared and Raman spectra. • A model based on multi-Franck–Condon (FC) progression has been used to analyze the photoluminescence (PL) spectra and to study oxygen-deficient centres (ODC) defects presented in fused silica, and their different emission pathways. • A PL decay time measurement a have been used to confirm the utility of the multi-FC progression to study the defects and track their different radiative transitions. [ABSTRACT FROM AUTHOR]

The present work focuses on the NIR emission of Nd3+ ions at 1.06 μm. Addition of fluoride content reduces the density and molar volume of the glasses. Judd-Ofelt analysis was applied to understand the absorption and emission spectra of the prepared glasses. The near-infrared emission was observed with two different excitation wavelengths at 582 nm and 805 nm. Spectroscopic quality factor found to be high for oxyfluoride glass. Luminescence intensity of oxide and oxyfluoride glass show highest at 1 mol% Nd 2 O 3 content. Judd-Ofelt analysis were applied to understand the radiative and non-radiative transition of Nd3+ doped glasses. LomheimDeS theory was applied to predict the branching ratios of the Nd3+ doped glasses which agrees well with 4F 3/2 → 4I 11/2 transition of obtained values from Judd-Ofelt theory. The quantum efficiency (η) of the 4F 3/2 level for Gd 2 O 3 doped and GdF 3 doped glasses were evaluated and found that oxide glass showed more than that of fluoride content. The prepared glasses are potential candidate for solid state emitting NIR transparent material. Photographs of Oxide and Oxy-fluoride glasses doped with Nd3+ ions and their energy level diagram. [Display omitted] • Neodymium doped phosphate glasses were synthesized using melt-quench technique. • Oxide and Oxyfluoride glasses were compared with optical spectroscopic techniques. • Radiative and non-radiative properties of oxide and oxyfluoride glasses were compared. • Oxide glasses show highest emission intensity than that of oxyfluoride glasses. • Luminescence decay times show higher values for oxide glasses than compared to oxyfluoride glasses. [ABSTRACT FROM AUTHOR]

Absorption, excitation, fluorescence and decay spectra are carried out at room temperature on Er 3+ (1%), Yb 3+ (4%): Cd .7 Sr .3 F 2 mixed single crystals. These crystals, with a good optical quality, are grown by the standard Bridgman method. This work concerns mainly the spectroscopic properties of the Er 3+ ions incorporated in a fluorite-type crystal. Using the room temperature absorption spectra, the standard Judd–Ofelt (JO) model is applied to absorption intensities of Er 3+ to obtain the three phenomenological intensity parameters by the least square fit procedure. The values obtained are in accordance with those of other fluoride hosts with good root mean square fitting. Compared to oxide materials, fluoride materials have, in general, low values ​​of Ω 2 . The low value of Ω 2 is correlated to the cubic nature of the site occupied by the rare earth in the host matrix. These JO intensity parameters are then applied to determine the radiative transition probabilities (A JJ′ ), radiative lifetimes (τ rad ) and branching ratios (β JJ′ ) of Er 3+ transitions. The green emission generated by the Er 3+ ions directly excited in UV level, consisting in three well-resolved major lines, is more intense than the one. We have measured the fluorescence lifetime, the cross-section emission, the gain and the radiative quantum efficiency for both green and red band emissions. The obtained results are in good agreement with those of other fluoride laser crystals. From, the obtained spectroscopic data we suggest that Cd .7 Sr .3 F 2 may offer green and red visible laser emission when doped with Er 3+ ions. [ABSTRACT FROM AUTHOR]

The influence of substituents of newly synthesized perylenediimides on their spectral properties and excited state relaxation has been studied by means of steady-state and time-resolved spectroscopy and quantum chemical calculations. Substituents at the perylene core cause broadening and shift of the absorption and fluorescence bands and also reduce the fluorescence quantum yield. Organic 4-tert-butylphenoxy substituents reduce the fluorescence yield by tens of percent by slightly reducing the oscillator strength of the radiative transition and by significantly increasing the non-radiative decay rate. We attribute both changes mainly to the distortion of the planarity of the perylene core. Bromine substituents reduce the fluorescence quantum yield by up to two orders of magnitude by opening an internal conversion channel. [ABSTRACT FROM AUTHOR]

Radioluminescent nuclear battery as a typical representative of small power device based on the generation and utilization of radioluminescence, which can stable energy supply for equipment in extreme environments. To date, the development of such nuclear battery is primarily limited by the weak radioluminescence intensity. In this work, a method of adding SiO 2 nanosphere coating to the fluorescent layer is proposed to solve the problem of weak radioluminescence and significantly improve the battery's output performance. The SiO 2 nanosphere coating can promote the radiative transition rate and quantum efficiency of the ZnS:Cu phosphor of fluorescent layer and the radioluminescent intensity of the ZnS:Cu fluorescent layer increases by 62.32%. And the maximum output power of the corresponding radioluminescent nuclear battery is enhanced by 51.59% compared with that before optimization, under the same X-ray excitation condition. The radioluminescent nuclear battery optimized based on the fluorescent layer with SiO 2 nanosphere coating increases its output power by more than 50% through radioluminescence enhancement. [Display omitted] • A method for enhancing the electrical output performance of the radioluminescent nuclear battery. • This method is simple to prepare and does not change the structure of the fluorescent material. • The addition of SiO 2 nanosphere coating to the fluorescent layer enhances the quantum efficiency of the fluorescent material, thereby increasing its radioluminescence intensity. • Improving the output performance of radioluminescent nuclear battery by increasing the intensity of radioluminescence. [ABSTRACT FROM AUTHOR]

Ho3+ and Eu3+ co-doping GdScO 3 crystal was successfully grown by special EFG method. The spectroscopic properties of the crystal were measured and analyzed. The absorption cross section was calculated to be 2.027 × 10−20 cm2 at 1161 nm. The J-O theory intensity parameters Ω t (t = 2, 4, 6), radiative transition rates, fluorescence branching ratios and radiative lifetimes were calculated. The Ho,Eu:GdScO 3 crystal has very strong emission at 2869 nm and the emission cross section was 13.524 × 10−21 cm2. The fluorescence lifetimes of the 5I 7 and 5I 6 levels were measured to be 4.457 ms and 1.265 ms. Confirmed that Eu3+ can be used as an effective deactivation ion of Ho3+ in GdScO 3 crystal. All those results show that the Ho,Eu:GdScO 3 crystal would be a potential laser material for ∼3 μm mid-infrared region. • Ho,Eu:GdScO 3 crystal was successfully grown. • The spectroscopic properties of the Ho,Eu:GdScO 3 crystal were analyzed. • J-O theory was applied to analyze fluorescence properties of the Ho,Eu:GdScO 3 crystal. • The energy transfer between Ho3+ and Eu3+ ions, spectroscopic characteristic of ∼3 μm emission were calculated and analyzed. [ABSTRACT FROM AUTHOR]

Since Pr 3+ ion has various emission bands in the visible region, Pr 3+ -doped materials are expected to be a potential candidate as laser media. In the present study, sulfide halide glasses based on Ga 2 S 3 –GeS 2 –CsX (X=Cl, Br), containing 20 mol% or more of CsX, and doped with Pr 3+ , were prepared for investigation of the visible spectroscopic properties of these glasses. The absorption edges were located around 460 nm and various emission bands in the visible region were observed with 450 nm excitation. Judd–Ofelt analyses were performed and total radiative transition rates from the 3 P j levels of Pr 3+ were estimated. The lifetime of the decay was approximately 10 μs for the emission at 654 nm due to the 3 P 0 → 3 F 2 transition. The emission quantum efficiencies were estimated from the ratio of the emission lifetime to the radiative transition lifetime calculated with the Judd–Ofelt analyses. The large efficiencies were attributed to the low phonon energies of the glass matrices compared with the energy gap between the 3 P 0 and the next lower level. [ABSTRACT FROM AUTHOR]

Intraband luminescence (IBL) is a prompt emission originating from the radiative intraband transitions of charge carriers during thermalisation. Despite its low intensity, IBL can hopefully enhance scintillation time resolution, for instance, in positron emission tomography. The continuous and structureless spectrum of IBL spans over the whole transparency region of a material. Exploiting a wide spectral sensitivity range of our instrumentation (0.77–10.6 eV), we have discovered a strong rise of IBL spectral yield in the NIR region in all studied compounds, which could not be explained within the available theoretical models of IBL. We have developed a new model attributing the NIR rise of the IBL spectrum to the phonon-assisted electron transitions within a single parabolic energy band, which yields a fair correspondence to our experimental data. [ABSTRACT FROM AUTHOR]

In this study, a series of well-crystallized Yb3+/Er3+/Tm3+-tridoped Y 2 O 3 –ZnO ceramic phosphors were prepared using sol–gel synthesis, and the phosphor structures were studied using X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The phosphors had excellent physical stability and porous structure. All phosphors generated blue, green, and red emission bands attributed to Tm: 1G 4 →3H 6 , Er: 2H 11/2 (4S 3/2)→4I 15/2 , and Er: 4F 9/2 → 4I 15/2 radiative transitions, respectively. The emissions were intensified twice by tuning the Tm3+ ratio in the host matrix Y 2 O 3 and ZnO parts. The color coordinates were adjusted by tuning both the Tm3+ concentration and the excitation laser pump power to shift the color coordinates and only enhance the brightness, respectively. Meanwhile, heating phosphors can also linearly adjust the color coordinates of the luminescence. Therefore, it can also be used as a fluorescence thermometer in the field of temperature sensor. The study findings will broaden the phosphor practical application potential. • The phosphors had excellent physical stability and porous structure. • The emission color was turned by adjusting the Tm3+ concentration. • Increasing excited power adjusted emission from white to blue at low Tm3+ concentrations. • Increasing excited power only increased brightness at high Tm3+ concentrations. [ABSTRACT FROM AUTHOR]

For the first time, a series of ceramic solid solutions of gadolinium tantalum niobates activated by europium was synthesized. A detailed interpretation of the obtained ceramics luminescence spectra was performed in the range of 580–630 nm for photoluminescence and 390–720 nm for cathodoluminescence. The transitions from 5D 0 , 5D 1 , 5D 2 and 5D 3 radiative levels of Eu3+ were observed in cathodoluminescence spectra of the samples. The main structural phase of the samples corresponded to the monoclinic structure with I2/a space group. The dependence of the europium luminescence bands Stark splitting on the Nb/Ta ratio in the material was studied for various radiative transitions. It was demonstrated that the distance between Eu3+ luminescence bands splitting increased in the solid solution series from GdNbO 4 to GdTaO 4. It can be due to an increase in the local field action on the Eu3+ ions. • Ceramic of Gd 0.94 Eu 0.06 Nb x Ta 1–x O 4 have been synthesized for the first time. • A detailed interpretation of Eu3+ luminescence spectra in GdNbTaO 4 has been performed. • The dependence of the Eu3+ levels Stark splitting on the Nb/Ta ratio was studied. • With an increasing of Ta content in the material, the Stark splitting increases. [ABSTRACT FROM AUTHOR]

In the present work, a series of zincate CaY 2 Sb 2 (ZnO 4) 3 :Eu3+ phosphors were successfully obtained via the conventional solid-state method at high temperature. The phase purity, morphology, element mapping, photoluminescence excitation/emission (PLE/PL), and decay time of the obtained phosphors were investigated systematically. Results show that the synthesized samples demonstrate the strongest red-emitting peak at 610 nm under the n-ultraviolet (n-UV) 395 nm excitation. The Judd-Ofelt parameters (Ω 2 , Ω 4), radiative transition rates, and branching ratios (β 0 J, J = 2, 4) of CaY 2 Sb 2 (ZnO 4) 3 :Eu3+ to explore the Eu3+-coordinated environment in the host matrix. The concentration quenching of CaY 2 Sb 2 (ZnO 4) 3 :2 x Eu3+ phosphors happened until at high doping concentration of x = 50 mol%. CaY 2 Sb 2 (ZnO 4) 3 :100 mol%Eu3+ sample presented the excellent thermal stability with abnormal thermal quenching behavior. Compared with the commercial Y 2 O 3 :Eu3+ red phosphor, the luminescent intensity of the prepared phosphor is 1.14 times stronger. The high internal quantum efficiency (IQE) of CaY 2 Sb 2 (ZnO 4) 3 :100 mol%Eu3+ phosphor is 79.20%. In addition, the fabricated red and white light-emitting diodes (w-LEDs) both emit bright light. The w-LED demonstrates a high color rendering index (R a = 96) and a low correlated color temperature (CCT = 5249 K). Therefore, the prepared red-emitting phosphor has a promising application in w-LEDs. • The phosphors have been firstly synthesized via high-temperature solid-state method. • The phosphors have abnormal thermal quenching performance. • The phosphor has a high IQE of 79.02%. • The fabricated w-LED has a high R a of 96 and a low CCT of 5249 K. [ABSTRACT FROM AUTHOR]

Ho:Lu 2 O 3 crystal was successfully grown by TGT method. The spectroscopic properties of the crystal were analyzed. The absorption cross section of Ho:Lu 2 O 3 were 0.307 × 10−20 cm2 at 1147 nm and 1.076 × 10−20 cm2 at 1929 nm. J-O theory was applied to analyze fluorescence properties of the Ho:Lu 2 O 3 crystal. The intensity parameters Ω t (t = 2,4,6), radiative transition rates, branching ratios and radiative lifetime were calculated. The Ho:Lu 2 O 3 crystal had very strong emission at 2027 nm and 2849 nm and emission cross sections were calculated to be 3.271 × 10−21 cm2 and 8.852 × 10−21 cm2, respectively. The fluorescence lifetimes of the Ho3+5I 7 and 5I 6 levels were measured to be 12.400 ms and 0.622 ms. All those results show that the Ho: Lu 2 O 3 crystal would be a potential laser material for mid-infrared region. • Ho: Lu 2 O 3 crystal was successfully grown by TGT method. • The spectroscopic properties of the Ho: Lu 2 O 3 crystal were analyzed. • J-O theory was applied to analyze fluorescence properties of the Ho:Lu 2 O 3 crystal. • The gain cross-section of Ho:Lu 2 O 3 crystal for ∼2 μm region and ∼3 μm region were calculated. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive study of the optical properties of Y 2 O 3 film with a monoclinic structure obtained by magnetron sputtering on a silica glass substrate. The parameters of band energy structure and emission characteristics of the film were determined by absorption, transmission, and photoluminescence spectroscopy. The dispersion of refractive index was established and the values of transparency gaps for direct and indirect interband transitions were determined. Optically active intrinsic centers were identified as vacancy (F - centers) and interstitial type (O i - centers) defects, which are characterized by distribution of radiative states over activation energy of emission quenching. Luminescence in the UV and visible spectral ranges is interpreted as triplet-singlet radiative transitions in self-trapped and bound excitons. The values of thermally activated barriers for flare up and quenching of exciton luminescence are determined, and the configuration-coordinate diagram is proposed. • Monoclinic Y 2 O 3 film was synthesized by magnetron sputtering. • UV emission is associated with F - centers and O i - centers. • Distribution of radiative states density over emission quenching was found. • Luminescence of two types of excitons (STE and BE) was registered. • Thermal activation barriers for flaring up and quenching of emission were determined. [ABSTRACT FROM AUTHOR]

Single crystals of the compositions Na 0.04 K 0.96 Y(WO 4) 2 (NKYW) and x mol% Er: Na 0.04 K 0.96 Y(WO 4) 2 (x = 1, 3, 5, 7) (Er: NKYW) have been successfully grown by the top-seeded solution growth (TSSG) method. The growth process parameters have been investigated in detail. X-ray diffraction (XRD) and Raman spectroscopy measurements showed that the K+ and Na+ cations occupied equivalent lattice sites and the crystal structure remained monoclinic. The spectral properties and energy transfer mechanisms of the single crystals doped with different concentrations of Er3+ ions were investigated. According to the Judd-Ofelt theory, the intensity parameters of the 5 mol% Er: NKYW crystal were calculated to be Ω 2 = 1.77 × 10−20 cm2, Ω 4 = 3.15 × 10−20 cm2, Ω 6 = 3.08 × 10−20 cm2, and the radiative transition probability of 4I 13/2 → 4I 15/2 was 541.25 s−1. The gain cross section of the 5 mol% Er: NKYW crystal at 1542 nm was determined to be 2.63 × 10−20 cm2, indicating that high-quality Er: NKYW single crystals have great potential for laser applications. • The NKYW and Er: NKYW crystals have been grown by the TSSG method, and optical parameters of the crystal are calculated. [ABSTRACT FROM AUTHOR]

A series of thulium-doped gallium-rich germano-gallate glasses are fabricated and thoroughly investigated. Their synthesis under an atmosphere-controlled glove box allows for a low hydroxyl concentration estimated at 14 wt ppm. From X-Ray diffraction spectroscopy and differential scanning calorimetry, the vitreous state of such gallium-rich BGG composition is confirmed. A structural analysis performed via Raman spectroscopy supports a three-dimensional interconnected glass network of gallium and germanium tetrahedra stabilized by Ba2+ ions as a charge compensator. From steady-state and time-resolved spectroscopies, Judd-Ofelt analysis is applied to determine the radiative transition rates, both absorption and emission cross-sections along with the resonant energy transfer microparameters. Through laser excitation at 808 nm, the intense 1.8 μm trivalent thulium emission is observed, while no concentration quenching is detected. Hence, the present work demonstrates gallium rich-BGG glasses doped with Tm3+ are suitable systems for IR photonic applications, notably for the development of high-power IR lasers. • Successful synthesis of low-OH crystal-free gallium-rich germano-gallate glasses doped with thulium. • Steady-state and time-resolved spectroscopies of the trivalent thulium luminescence have been carried out. • Thorough Judd-Ofelt investigation has been performed. • No quenching of concentration has been reported up to 2 mol% of Tm3+. [ABSTRACT FROM AUTHOR]

In recent years, upconversion photoluminescent micro/nanocrystals with unique anti-Stokes luminescence properties have shown high application value in many relevant fields. In this work, pure tetragonal phase NaLa(MoO 4) 2 :Yb3+/Ho3+ microspheres have been synthesized by a solvothermal method in the presence of oleic acid and 1-octadecene. Under the excitation of 980 nm laser, NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals emit red, green and near infrared upconversion luminescence with peak wavelengths at 660/643 nm, 541 nm, and 756 nm. Based on the analysis of excitation power-dependent upconversion luminescence intensities and energy level diagram of Yb3+/Ho3+, electronic transition pathways in the energy transfer processes for upconversion luminescence of NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals are studied. For red upconversion luminescence at 660/643 nm, the predominant population pathway to state 5 F 5 (Ho3+) is "Yb3+ (2 F 5/2) + Ho3+ (5 I 7) → Yb3+ (2 F 7/2) + Ho3+ (5 F 5)". While, "Yb3+ (2 F 5/2) + Ho3+ (5 I 6) → Yb3+ (2 F 7/2) + Ho3+ (5 F 4 /5 S 2)" process accounts for the population of state 5 F 4 /5 S 2 (Ho3+) for radiative transitions of upconversion luminescence at 541 and 756 nm. Energy back transfer contributes to the intense red upconversion luminescence at 660/643 nm. These electronic transition pathways in energy transfer processes are further confirmed by the analyses based on energy level mismatch and luminescent lifetimes. [Display omitted] • Electronic transition pathways for energy transfer upconversion luminescence in NaLa(MoO 4) 2 :Yb3+/Ho3+ microcrystals. • Predominant population pathway for red upconversion luminescence at 660/643 nm of Ho3+ is elucidated. • Analyses of energy level mismatch and luminescent lifetimes confirm the proposed electronic transition pathways. [ABSTRACT FROM AUTHOR]

The Er3+:YPO 4 crystals co-doped with different concentrations of Yb3+ (7.5 at.% and 11.5 at.%) were successfully grown by high-temperature solution method with Pb 2 P 2 O 7 as cosolvent. Crystal growth, structures and spectroscopic characterizations, including polarized absorption spectra, polarized fluorescence spectra and lifetime, were systematically explored and compared. The absorption FWHM at around 975 nm is 17.1 nm for σ- polarizations and 12.0 nm for π- polarizations, which makes Er3+/Yb3+:YPO 4 crystal suitable for effective pumping by InGaAs laser diode. Based on J-O theory, the spectroscopic parameters, including J-O intensity, oscillator strength, line strength, fluorescence branching ratios, spontaneous transition rates and radiative lifetime were calculated systematically. Furthermore, four intense emission peaks at around 1505, 1537, 1561 and 1586 nm can be observed in the polarized fluorescence spectra. Theoretically, different frequencies interactions between these wavelengths may be used for the application of generating radiation in the range of 2.9–10.2 THz. The results show that Er3+/Yb3+:YPO 4 crystal may be a potential laser material of 1.5–1.6 μm. [Display omitted] • The Er3+/Yb3+:YPO 4 crystal was grown successfully from Pb 2 P 2 O 7 solution. • Spectral parameters of Er3+ ions were calculated in detail based on J-O theory. • Intense multi-wavelength emissions can be observed in the range of 1.5–1.6 μm. [ABSTRACT FROM AUTHOR]

Here we present a summary of the theoretical studies of the emission rates modifications of emitter placed inside or near the subwavelength nanoparticle that are embedded in a medium. The change in spontaneous emission rate as a function of the effective refractive index of the nanocomposite, as well as on the refractive indices of NPs and the substance filling the space between them is presented. Both naked and coated nanoparticles are considered. [ABSTRACT FROM AUTHOR]

We report two new ternary metal halide scintillators, KBa 2 I 5 and K 2 BaI 4 , activated with divalent europium. Single crystal X-ray diffraction measurements confirmed that KBa 2 I 5 has a monoclinic structure (P2 1 /c) and that K 2 BaI 4 has a rhombohedral structure (R3c). Differential scanning calorimetry showed singular melting and crystallization points, making these compounds viable candidates for melt growth. We grew 13 mm diameter single crystals of KBa 2 I 5 :Eu 2+ and K 2 BaI 4 :Eu 2+ in evacuated quartz ampoules via the vertical Bridgman technique. The optimal Eu 2+ concentration was 4% for KBa 2 I 5 and 7% for K 2 BaI 4 . The X-ray excited emissions at 444 nm for KBa 2 I 5 :Eu 4% and 448 nm for K 2 BaI 4 :Eu 7% arise from the 5d–4f radiative transition in Eu 2+ . KBa 2 I 5 :Eu 4% has a light yield of 90,000 photons/MeV, with an energy resolution of 2.4% and K 2 BaI 4 :Eu 7% has a light yield of 63,000 ph/MeV, with an energy resolution of 2.9% at 662 keV. Both crystals have an excellent proportional response to a wide range of gamma-ray energies. [ABSTRACT FROM AUTHOR]

Strong and broadband 2.7 μm fluorescence with effective emission linewidth of 140.4 nm has been achieved in 1 mol% Yb 2 O 3 and 1 mol% Er 2 O 3 co-doped ZnO modified tungsten tellurite glass under an excitation from a 980 nm laser diode. The influences of Yb3+ concentration on 2.7 μm spectroscopic properties of Yb3+/Er3+ co-doped ZnO modified tungsten tellurite glasses were analyzed by absorption spectra, emission spectra and lifetime measurement. Long lifetime of 4I 11/2 level (649.4 μs), high spontaneous radiative transition probability (65.1 s−1), large emission cross section (8.27 × 10−21 cm2) and figure of merit (5.37 × 10−24 cm2s) near 2.7 μm ensure intense 2.7 μm emission. Furthermore, the energy transfer coefficients between Yb3+ and Er3+ ions are quantitatively determined to explain the reinforcement of 2.7 μm fluorescence. Therefore, Yb3+/Er3+ co-doped ZnO modified tungsten tellurite glasses with better 2.7 μm spectroscopic performances are predominant candidates in constructing broadband mid-infrared optical amplifiers and tunable fiber lasers. • Strong and broadband 2.7 μm fluorescence with effective emission linewidth of 140.4 nm has been achieved in 1 mol% Yb 2 O 3 and 1 mol% Er 2 O 3 co-doped ZnO modified tungsten tellurite glass under an excitation from a 980 nm laser diode. • The present glasses are characterized by long lifetime of 4I 11/2 level (649.4 μs), high spontaneous radiative transition probability (65.1 s−1), broad effective emission linewidth (140.4 nm), large emission cross section (8.27 × 10−21 cm2) and figure of merit (5.37 × 10−24 cm2s) near 2.7 μm. • Yb3+/Er3+ co-doped ZnO modified tungsten tellurite glasses with better 2.7 μm spectroscopic performances are predominant candidates in constructing broadband mid-infrared optical amplifiers and tunable fiber lasers. [ABSTRACT FROM AUTHOR]

The optical transition properties of Tm3+ in oxyfluoride tellurite glass were determined by the Judd–Ofelt theory. The radiative transition rates, fluorescence branching ratios, and intrinsic lifetime for interesting transitions or level were obtained. The optimum doping concentration of Tm3+ for sample was examined, and the optimal concentration for upconversion luminescence was 0.1% Tm 2 O 3. The main reason for concentration quenching was nonradiative energy transfer through the cross-relaxation mechanism. In addition, two-photon processes for near-infrared 3H 4 →3H 6 emission and three-photon processes for blue 1G 4 →3H 6 emission of Tm3+ were confirmed by analyzing the dependence of upconversion intensities on the 980 nm fiber laser. The temperature-sensing properties of Tm3+ in oxyfluoride tellurite glass were investigated using 3F 2,3 → 3H 6 (698 nm) and 3H 4 →3H 6 (801 nm) excited at 980 nm, and the 3F 2,3 and 3H 4 states of Tm3+ were thermally coupled levels. • Optical transition properties of Tm3+ in the studied fluorescent glass were evaluated. • 1G 4.→3H 6 emission of Tm3+ is a three photon process and the upconversion near-infrared 3H 4 →3H 6 emission is a two-photon process under 980 nm irradiation. • The temperature sensing properties of Tm3+ in oxyfluoride tellurite glass were investigated by using 3F 2,3 and 3H 4 as thermal coupling energy levels excited at 980 nm. [ABSTRACT FROM AUTHOR]

In this study, the laser sintering technique was used to obtain Er3+/Yb3+ co-doped silica glasses for up-conversion (UC) luminescence for the first time. Further, structural analysis of the glass sample was conducted via XRD, SEM and EDS measurements. Based on the measured absorption spectrum, important spectroscopic parameters including three intensity parameters Ω t (t = 2, 4 and 6), theoretical and experimental line strengths, spontaneous transition probabilities, branching ratios and radiative lifetimes, were calculated using the Judd-Ofelt (J-O) theory. The UC properties of Er3+/Yb3+ co-doped silica glasses were investigated upon the excitation of a 976 nm laser. It has been experimentally confirmed that the green and red UC luminescences corresponding to the radiative transitions of Er3+: 2H 11/2 → 4I 15/2 (green), 4S 3/2 → 4I 15/2 (green) and 4F 9/2 → 4I 15/2 (red) were achieved. This result is consistent with those of the J-O theoretical analysis. Additionally, the energy transfer mechanism between Er3+ and Yb3+, which is responsible for the UC process, was discussed based on their dependence on the pump power. The obtained results indicated that the Er3+/Yb3+ co-doped silica glasses manufactured using the laser sintering technique can be promising for the application of short-wavelength lasers. • A non-CVD method, namely the laser sintering technique, was adopted. • Er3+/Yb3+ co-doped UC luminescent silica glasses was fabricated. • The silica glasses have exhibited excellent optical and spectroscopic properties. • Strong UC emissions were experimentally observed. • The experimental result is in agreement with those of the J-O theoretical analysis. [ABSTRACT FROM AUTHOR]

A series of Eu3+ doped ZnS red emitting phosphors were synthesized by conventional low temperature solid state reaction technique. The structural and spectroscopic characteristics of the prepared materials were examined by theoretical and experimental methods. The XRD results confirm the formation of hexagonal structured ZnS material. Similar morphology is obtained from TEM and SEM analysis and the particle size and grain size were calculated. The compositional analysis using EDS confirms the atomic percentage present in the materials. The optical band gap energy of the samples varied from 3.59 to 3.43 eV. The PL emission under excitation 390 nm has greater emission intensity at concentration x = 0.1 in Zn (1- x) S: x Eu3+ material. The intense red emission (614 nm) for concentration x = 0.1 have CIE coordinates (0.6090, 0.3905) with color purity 90.41% and CCT 1629.26 K. The site symmetry of Eu3+ ions was explained using PL emission spectra. The intensity parameters Ω 2 , Ω 4 and Ω 6, radiative properties like branching ratio (β R), transition radiative parameter (A R) , stimulated emission cross section σ e , radiative life time (τ R) was calculated from Judd-Ofelt theory. The luminescence decay kinetics was analyzed and the life time of material was calculated in millisecond (ms) range. The strong and intense red emission and the improved stimulated emission cross section offer Eu3+ doped ZnS material useful for designing optoelectronic device applications. • Synthesis of Pure and varying concentration (1, 2, 3, 10, 20 and 30%) of Eu3+ doped ZnS phosphor via low temperature solid state reaction method. • Spectroscopic intensity parameters using JO theory and the radiative parameters were investigated. • All the prepared phosphors exhibit intense red emission. • The results suggest the possibility of these phosphors being applied in the field of designing various optoelectronic devices. [ABSTRACT FROM AUTHOR]

Spectroscopic properties and dynamic analysis play a significant role during the design and development of novel luminescent materials. In this work, Er3+ doped NaYF 4 nanoparticles were successfully synthesized by coprecipitation method. The absorption spectrum, fluorescence spectra, and decay curves were measured at room temperature. The spectroscopic properties, including the radiative and nonradiative transition probability, fluorescent branch ratio, cross-relaxation rate and the fluorescence lifetime, were calculated based on the Judd-Ofelt theory. Furthermore, the rate equation models were established to analyze the dynamic processes of three-photon near-infrared quantum cutting luminescence. The time-dependent population densities of excited levels of Er3+ ions were simulated and the theoretical quantum efficiency was calculated to be 252.40%, which is consistent with our experimental results. • Three-photon NIR QC luminescent materials NaYF 4 :Er3+ NPs were synthesized. • The spectroscopic properties were investigated through J-O theory. • The rate equation models were established to analyze the dynamic of QC processes. • The time-dependent population densities of Er3+ levels were simulated. • The upper limit theoretical quantum efficiencies were evaluated to be 252.40%. [ABSTRACT FROM AUTHOR]

Sm-doped Sr 5 (PO 4) 3 Cl was prepared by a solution combustion synthesis in the air atmosphere. The pure hexagonal phases of the samples were confirmed via the XRD, Raman, and FT-IR measurements. The typical microrod shape of the products was also demonstrated by SEM, TEM, and HRTEM images. The spectral properties and lifetimes were applied to characterize the luminescence of the samples as-prepared and subsequently heated in the air atmosphere. The luminescence of as-prepared Sm-doped Sr 5 (PO 4) 3 Cl contains a broad emission band and a group of narrow lines, which are ascribed to the radiative transitions of 4f5d→4f and 5D 0 →7F J (J = 0, 1, 2) of Sm2+ ions, respectively. It indicates that the Sm3+ can be successfully reduced to Sm2+ ions in hexagonal Sr 5 (PO 4) 3 Cl prepared by combustion synthesis. The temperature dependent luminescence spectra and decay curves of Sm2+ were measured in a very wide temperature region from 10 K to 300 K. The thermal quenching and activation energy of Sm2+ doped Sr 5 (PO 4) 3 Cl were reported. The crystal field energy level diagram and excitation mechanism of Sm2+ ions-doped Sr 5 (PO 4) 3 Cl were characterized by the high resolution luminescence at low temperature. The luminescence of Sm2+ in Sr 5 (PO 4) 3 Cl shows a great dependence on heating temperature in the air atmosphere (50–700 °C). The heating treatments at the elevated temperature depress Sm2+ emission along with the appearance of Sm3+ ions. The temperature-induced changes in the modification of the spectral components could be applied as potential luminescence thermometry. • Sm-doped Sr 5 (PO 4) 3 Cl microrod was prepared by solution combustion synthesis. • Abnormal Sm3+.→Sm2+ reduction can be realized in hexagonal Sr 5 (PO 4) 3 Cl. • Temperature quenching of the 5D 0 multiplet of Sm2+ has been determined. • Heating treatment in air atmosphere exerts great influence on emission components. [ABSTRACT FROM AUTHOR]

Abstract: The Judd–Ofelt parameters of Er3+ in the partially disordered calcium lithium niobium gallium garnet are calculated using absorption spectra. The results ( ; ; ) are used to calculate the radiative lifetimes of the Er3+ energy levels up to 4G11/2 and the branching ratios of the radiative transitions originating on them. The luminescence lifetimes of Er3+ excited levels 4I13/2, 4I11/2, 4F9/2, (4S3/2, 2H211/2) and 2H29/2 are also presented. [Copyright &y& Elsevier]

Abstract: Different concentrations (0.1, 0.5, 1.0 and 2.0mol%) of Er3+-doped lead telluroborate glasses were prepared by conventional melt quenching method. Up on 514.5nm laser excitation, the near infrared luminescence due to the 4I13/2→4I15/2 transition was analyzed. The absorption and emission spectra were used to determine the different spectroscopic parameters by means of the Judd–Ofelt and the McCumber theories. The obtained Judd–Ofelt intensity parameters were used to obtain the radiative transition probability, fluorescence branching ratio and radiative lifetime of the 4I13/2 emission state. The effect of Er3+ concentration on the emission intensity of 4I13/2→4I15/2 transition was discussed. The Stark-level energies of 4I13/2 excited and 4I15/2 ground states were evaluated using both the absorption and emission measurements. The wavelength dependent gain coefficient, G(λ) of 4I13/2→4I15/2 transition of Er3+ ion was determined using the absorption and emission cross-sections. The suitability of this glass as a host for Er3+-doped broad-band amplifiers and its advantage over other glasses were discussed. [Copyright &y& Elsevier]

Abstract: Single crystals of α-Sm3+:Na3Y(VO4)2 have been grown by the flux growth method. The absorption (300K) fluorescence (4.2 and 300K) and excitation (7 and 300K) spectra as well as the fluorescence dynamics of the Sm3+-doped title crystals are presented and analyzed in detail. The energy transfer between Sm3+–Sm3+ as well as from VO4 3− to Sm3+ were studied in detail. A Judd–Ofelt intensity analysis of the absorption (300K) spectrum has been applied for determination of Ω λ parameters which in turn have been used in calculation of the radiative transition probability factor (A), fluorescence branching ratios (β), natural (radiative) lifetime of the 4G(4)5/2 level of Sm3+ and emission cross-section (σ em ). For the first time very large lifetimes of the Sm3+ fluorescence level have been observed. [Copyright &y& Elsevier]