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The present study investigated the impact of incorporating copper nanoparticles (CuNPs) on the optical properties of erbium-doped borate glasses. Through melt-quenching and heat treatment techniques, glasses with varying Cu 2 O concentrations (x = 0–5 mol%) were synthesized. Physical and structural analyses revealed that Cu ions serve as effective network modifiers. They foster the formation of a greater proportion of BO 4 tetrahedra and thus enhancing glass homogeneity. Optical absorption spectra demonstrate a distinct modulation of Er3+ absorption bands with Cu 2 O embedding, indicating the formation of CuNPs, as validated by the emergence of surface plasmon resonance bands. This structural evolution results in a noticeable reduction in the bandgap energy, signifying improved semiconducting behavior. Judd-Ofelt analysis highlighted the profound influence of CuNPs on hypersensitive transitions, thereby affecting oscillator strength. Photoluminescence measurements revealed amplified emission in the visible red and near infrared (NIR) region, attributed to the synergistic effects of CuNPs and Er3+ ions, with 5 mol % Cu 2 O exhibiting the highest emission intensity. Analysis of the radiative properties validates the enhancement of the emission cross-section, gain bandwidth, optical gain and radiative transitions. These enhancements contribute to a notable increase in the branching ratio from 0.91 % to 5.41 % accompanied by an increase in the quantum efficiency from ∼79 % to ∼90 %. Moreover, decay analysis revealed a notable enhancement in lifetime from 3.03 ms to 15.74 ms, which is indicative of enhanced radiative transitions. Overall, the incorporation of CuNPs into erbium-doped borate glasses facilitates significant enhancements in physical, structural, and optical properties. This positions them as promising materials for a wide array of optoelectronic applications. This comprehensive study sheds light on the complex interplay between CuNPs and erbium-barium borate glasses, offering valuable insights for the development of advanced optoelectronic materials with enhanced performance and functionality. [Display omitted] [ABSTRACT FROM AUTHOR]

The single crystals of CsI-Yb2+ were grown, and their spectroscopic studies were conducted. The observed luminescence in CsI-Yb2+ is due to 5d–4f transitions in Yb2+ ions. Using time-resolved spectroscopy, spin-allowed and spin-forbidden radiative transitions of ytterbium ions at room temperature were found. The excitation spectra of Yb2+ luminescence bands were obtained in the range of 3–45 eV. The mechanism of charge compensation of Yb2+ ions in a CsI crystal was also studied, the spectrum of the thermally stimulated depolarization current was measured, and the activation energies of the two observed peaks were calculated. These peaks belong to impurity–vacancy complexes in two different positions. The charge compensation of Yb2+ occurs via cation vacancies in the nearest-neighbor and next-nearest-neighbor positions.The Yb2+ ions are promising dopants for CsI scintillators and X-ray phosphors in combination with SiPM photodetectors. [ABSTRACT FROM AUTHOR]

Crystal-field perturbation is theoretically the most direct and effective method of achieving highly efficient photoluminescence from trivalent lanthanide (Ln3+) ions through breaking the parity-forbidden nature of their 4f-transitions. However, exerting such crystal-field perturbation remains an arduous task even in well-developed Ln3+-doped luminescent nanocrystals (NCs). Herein, we report crystal-field perturbation through interstitial H+-doping in orthorhombic-phase NaMgF3:Ln3+ NCs and achieve a three-orders-of-magnitude emission amplification without a distinct lattice distortion. Mechanistic studies reveal that the interstitial H+ ions perturb the local charge density distribution, leading to anisotropic polarization of the F− ligand, which affects the highly symmetric Ln3+-substituted [MgF6]4− octahedral clusters. This effectively alleviates the parity-forbidden selective rule to enhance the 4f–4 f radiative transition rate of the Ln3+ emitter and is directly corroborated by the apparent shortening of the radiative recombination lifetime. The interstitially H+-doped NaMgF3:Yb/Er NCs are successfully used as bioimaging agents for real-time vascular imaging. These findings provide concrete evidence for crystal-field perturbation effects and promote the design of Ln3+-doped luminescent NCs with high brightness. Lanthanide-doped inorganic nanocrystals are promising for optical imaging and biomedical applications. Here authors show that interstitial H+ doping-induced crystal-field perturbation enhances the photoluminescence intensity of lanthanide-doped inorganic nanocrystals. [ABSTRACT FROM AUTHOR]

The photoluminescence of Au(I) complexes is generally characterized by long radiative lifetimes owing to the large spin-orbital coupling constant of the Au(I) ion. Herein, we report three brightly emissive Au(I) coordination compounds, 1, 2a, and 2b, that reveal unexpectedly short emission lifetimes of 10–20 ns. Polymorphs 2a and 2b exclusively exhibit fluorescence, which is quite rare for Au(I) compounds, while compound 1 reveals fluorescence as the major radiative pathway, and a minor contribution of a microsecond-scale component. The fluorescent behaviour for 1–2 is rationalized by means of quantum chemical (TD)-DFT calculations, which reveal the following: (1) S0–S1 and S0–T1 transitions mainly exhibit an intraligand nature. (2) The calculated spin-orbital coupling (SOC) between the states is small, which is a consequence of overall small metal contribution to the frontier orbitals. (3) The T1 state features much lower energy than the S1 state (by ca. 7000 cm−1), which hinders the SOC between the states. Thus, the S1 state decays in the form of fluorescence, rather than couples with T1. In the specific case of complex 1, the potential energy surfaces for the S1 and T2 states intersect, while the vibrationally resolved S1–S0 and T2–S0 calculated radiative transitions show substantial overlap. Thus, the microsecond-scale component for complex 1 can stem from the coupling between the S1 and T2 states. [ABSTRACT FROM AUTHOR]

Novel ternary fluoro-germano-tellurite (GTS) glasses doped with Er3+ ions with 0.5 mol% and 1.0 mol% were fabricated by a conventional melt and quenching method and investigated using methods of optical spectroscopy. The room-temperature absorption spectrum was recorded and analyzed to determine radiative transition rates, radiative lifetimes, and branching ratios of Er3+ luminescence. Decay curves of Er3+ luminesccence were recorded and analyzed. Temperature dependences of emission spectra and absorption spectra in the region from RT (room-temperature) up to 675 K were studied in detail. The contribution of competing radiative and nonradiative processes to the relaxation of luminescent levels of Er3+ was assessed. Absolute and relative sensitivity were established utilizing the comprehensive model based on thermally coupled 2H11/2/4S3/2 excited states of erbium. The high quantum efficiency of the first erbium-excited state and value of gain coefficient indicate that GTS:Er glass system can be considered as conceivable NIR (near infrared) laser material as well. [ABSTRACT FROM AUTHOR]

We report a comparative study of coordination behaviour of 2-(2-aminophenyl)benzothiazole (NH2-pbt) and its phosphorus-containing derivative, α-aminophosphine oxide (PCNH-pbt), towards zinc halides. The corresponding coordination compounds [Zn(L)2Hal2] (L = PCNH-pbt, Hal = Cl, 1 and Hal = Br, 2) and [Zn(L')Hal2] (L' = NH2-pbt, Hal = Cl, 3 and Hal = Br, 4) were obtained as single phases. As evidenced by single-crystal X-ray diffraction analysis, L' ligand coordinates to Zn in a chelate manner via two N atoms. Despite a similar coordination mode in complexes 3 and 4, the spatial geometry of the ligand differs notably, which implies a relatively high flexibility of NH2-pbt. The L ligand exhibits another coordination mode, binding with Zn only via the oxygen of the P=O group. The differences in the structures of NH2-pbt, 3 and 4, and their counterparts, PCNH-pbt, 1 and 2, induce differences in their solid-state photoluminescence properties. The former group of the compounds exhibits conventional single-band emission, while the latter group reveals two bands. The minor band at 450 nm is ascribed to a radiative transition for the regular amine species, while the major band at 520–550 nm can be associated either with the proton-transferred imine species (ESIPT mechanism) or with a charge transfer state (TICT) with a different geometry. [ABSTRACT FROM AUTHOR]

A high-luminescent, blue-light excitable europium(III) coordination complex, [Eu(µ2-OC2H5)(btfa)(NO3)(phen)]2phen (1) {btfa = benzoyl trifluoroacetone, phen = 1,10-phenantroline}, has been synthesized and investigated. The complex was characterized by infrared (IR) and photoluminescence (PL) spectroscopy. The PL emission spectra of powder samples registered in a range of 10.7–300 K exhibit characteristic metal-centered luminescence bands, assigned to internal radiative transitions of the Eu3+ ion, 5D1→7Fj and 5D0→7Fj (j = 0–4). The high-resolution spectrum of the transition 5D0→7F0 shows that it consists of two narrow components, separated by 0.96 meV, which indicates the presence in the matrix of two different sites of the Eu3+ ion. The splitting pattern of 5D0→7Fj (j = 0–4) transitions indicates that europium ions are located in a low-symmetry environment. The absolute quantum yield and the sensitization efficiency were determined to be 49.2% and 89.3%, respectively. The complex can be excited with low-cost lasers at around 405 nm and is attractive for potential applications in optoelectronics and biochemistry. [ABSTRACT FROM AUTHOR]

Based on the local surface plasmon resonance effect of Ag nanolayer, the luminescence enhancement in the visible light range of multilayer thin film has been investigated combined with metal/spacer molecule/photoluminescence material structure. The luminescence enhancement effect of multilayer thin films can be improved by adjusting the spin-coating number of Ag nanolayer and SiO 2 spacer in the multilayer structure. At the same time, the mechanism of enhanced luminescence has been analyzed according to the change in fluorescence lifetime. The effect of the coupling between Ag nanolayer and luminescence layer on the radiative transition rate and fluorescence quantum yield have been discussed. The up-conversion luminescence intensity of the noble metal-modified multilayer thin film can be further improved by combining the multilayer structure with sensitized layer. • The emission intensity of thin films are improved via the LSPR effect of Ag nanolayer. • On the basis of Ag@Tm/Yb structure, SiO 2 spacer layer is introduced to further enhance the upconversion luminescence. • The mechanisms of luminescence enhancement in the multilayer thin films are analyzed. • More than 20 times emission enhancement is achieved in the Ag@SiO 2 @Tm/Yb@Yb multilayer thin films. [ABSTRACT FROM AUTHOR]

Results of studies by scanning electron microscopy and photoluminescence (PL) of structural features and radiative transitions of ZnO:Mg films grown by atmospheric pressure metal-organic chemical vapor deposition (APMOCVD) on silicon substrates are presented. Different ZnO:Mg microstructures from polycrystalline films with smooth morphology to columns and hexagonal rods are effectively formed in a wide temperature range 190-450 °C using two compositions of a mixture of zinc and magnesium (5 and 10 wt. %) acetylacetonates (ZnAA and MgAA, respectively) as precursors. The substrate temperatures have a drastic effect on the crystallinity and morphology of ZnO films. A column shaped ZnO microstructure is formed at a substrate temperature above 350 °C. The MgАА content in the mixture of precursors also affects the morphology of polycrystalline films. At lower substrate temperatures (200-320 °C), grown ZnO:Mg samples with MgAA content of 10 wt. % have a surface morphology characterized by enlarged grains compared to samples grown with MgAA 5 wt. %, whereas high substrate temperatures (350-450 °C) promote to form a surface morphology with rod-like structures in both cases: 5 and 10 wt. % of MgAA content. The growth rate of ZnO structures increases with increasing substrate temperatures. The PL emission spectra of samples with 10 wt. % MgAA demonstrate increased near band edge (NBE) emission and suppress defect level emission compared to samples with 5 wt. % MgAA. Therefore, we can conclude that magnesium acts as an isoelectronic impurity improving NBE PL emission due to gettering of defects. Mg also causes an increase in grain size, improving the crystalline perfection of ZnO:Mg polycrystalline films grown at low substrate temperatures, as well as helps to grow hexagonal rods at higher substrate temperatures. Thus, Mg-doped ZnO microstructures grown in the high temperature range could be an effective photocatalyst. [ABSTRACT FROM AUTHOR]

Gd2(WO4)3 and Gd2(WO4)3:0.5% Tm3+, 10% Yb3+ nanopowders have been prepared by the Pechini method and solid-state sintering. According to X-ray diffraction results, the materials prepared by the Pechini method are more uniform in phase composition. Optimal synthesis conditions were defined: t = 900°C and τ = 1 h for Gd2(WO4)3 and t = 950°C and τ = 3 h for Gd2(WO4)3:0.5% Tm3+, 10% Yb3+. The surface morphology of the materials has been studied by scanning electron microscopy. The samples prepared by solid-state sintering have been found to be highly agglomerated, and large agglomerates have been shown to persist even after ultrasonic processing. The average size of the doped and undoped nanoparticles prepared by the Pechini method has been determined to be 44.0 and 47.6 nm, respectively. Luminescence spectra of Gd2(WO4)3:0.5% Tm3+, 10% Yb3+ were measured and compared the intensities of the Tm3+1G4 → 3H6, 1G4 → 3F4, 3F1,2→3H6, and 3H4 → 3H6 radiative transitions in the materials prepared by both methods. The data obtained in this study demonstrate that the Pechini process is a preferable and promising method for the synthesis of Gd2(WO4)3 and Gd2(WO4)3:Tm3+,Yb3+ nanopowders. [ABSTRACT FROM AUTHOR]

In this study, Ho3+-doped 0.825K0.5Na0.5NbO3-0.175Sr(Yb0.5Nb0.5)O3 luminescence transparent ceramics were prepared via the traditional solid-state sintering method. The structure and optical properties of the ceramics before and after polarization were studied at 40 kV cm−1 for 0.5 h. With the increase of Ho content, the phase structure of the ceramics changed from a pseudo-cubic phase to the tripartite and the orthorhombic phases, and the light transmittance decreased. The ceramics demonstrated an up-conversion luminescence characteristic under the excitation of a 980 nm laser, and the emission wavelengths were 550 and 670 nm. The best up-conversion luminescence performance was obtained when the Ho content was 0.1%. Moreover, the polarization markedly enhanced the luminescence performance of the 0.825K0.5Na0.5NbO3-0.175Sr(Yb0.5Nb0.5)O3-0.1%Ho ceramics due to the increased possibility of energy-level radiative transition of rare-earth Ho3+ ions and reduction of the Eg value of the ceramic. [ABSTRACT FROM AUTHOR]

This work reports on the analysis of structural and spectroscopic properties of the fluoroindate glasses co-doped with Er3+/Ho3+. Structural analysis showed that erbium and holmium ions were modifier ions and depolymerizedof the fluoroindate glass network. The energy transfer processes between rare - earth ions in fluoroindate glasses pumped by and 980 nm laser diode have been also examined. Due to partial Er3+ → Ho3+ energy transfer and superposition of Er3+: 4I 11/2 → 4I 13/2 (2.77 μm)+ Ho3+: 5I 6 → 5I 7 (2.85 μm) radiative transitions in fluoroindate glass co-doped with 0.8ErF 3 /1.6HoF 3 , a broadening 3 μm luminescence (Δλ= 201 nm) was obtained. The overall energy transfer efficiency η ET1 + η ET2 was calculated to be 95% indicating efficient sensitization of the holmium ions by erbium. [ABSTRACT FROM AUTHOR]

Y2O3:Er3+ translucent ceramics was fabricated with addition of La(OH)3 nanopowder as a sintering aid. The influence of La(OH)3 addition on the microstructure, transmittance and upconversion luminescence of Y2O3:Er3+ ceramics was investigated in detail. The results show that the ceramics sample with 5 mol % La(OH)3 additives exhibits finer microstructure with fewer pores and higher optical transmittance than others. It was proved that La(OH)3 additives could greatly reduce the porosity and improve the transparency of Y2O3:Er3+ ceramics. By using a 980 nm diode laser as a pumping source, the Y2O3:Er3+ ceramics gave bright visible upconversion luminescence, which was ascribed to the radiative transitions of 2H11/2,4S3/2 →4I15/2 and 4F9/2 →4I15/2 of Er3+ ions, respectively. The possible upconversion mechanism has been proposed accordingly. [ABSTRACT FROM AUTHOR]

A series of glasses by melting quenching method fabricated for spectroscopic investigations of Dysprosium (Dy3+) particle ions deposited on Antimony (Sb) - Magnesium (Mg) - Strontium (Sr) Oxyfluoroborate (BSbMgfSr) glasses. The structural and optical characterizations such as XRD, UV-VIS-NIR absorption spectroscopy, photoluminescence (PL) (excitation and emission) were accomplished to study the properties of prepared glasses. The transitions from lowest energy state to an excited state in RE3+ ions were identified using optical UV-NIR absorption spectra. By the use of Judd-Ofelt theory the J-O intensity parameters Ωλ (λ = 2, 4, 6) have been evaluated utilizing the absorption spectra with the determination of experimental (fexp) and calculated (fcal) oscillator strengths. The emission of light from glass system was concluded through PL spectra (Excitation and emission) for Dy3+ion. The radiative properties resembling radiative transition probability (AR), radiative-lifetime (τR), and branching-ratio (β) of the glasses have also estimated. Stimulated emission cross-section (σse) of the glasses also calculated for the feasibility of lasing applications. Experimental lifetime (τexp) of the decay curves of the BSbMgfSrD glasses were also calculated upon excitation by suitable wavelengths of all various concentrations of the RE3+ ions. [ABSTRACT FROM AUTHOR]

Absorption, fluorescence, and phosphorescence spectra of metal complexes of 4-tert-butylphenyl-substituted tetra(1,4-diazepino)porphyrazine MPADz4Ph8′ (M = Mg, Zn; PA = porphyrazine; Dz = diazepine; Ph = phenyl; Ph′ = 4-tert-butylphenyl) were recorded in DMF at 293 and 77 K. The Q(0–0) absorption bands of MgPADz4Ph8′ and ZnPADz4Ph8′ did not show signs of splitting, i.e., corresponded to the monomeric form. Singlet–triplet gaps of 4700 cm–1 for the Mg complex and 4800 cm–1 for the Zn complex were determined from fluorescence and phosphorescence spectra. Fluorescence quantum yields and lifetimes were measured. Rate constants of S1,2 → S0 radiative transitions and total rate constants of nonradiative deactivation of the S1,2 states were determined. Internal conversion rate constants were estimated. Conformer geometries of MgPADz4Ph8 (in the 6H tautomeric form) were calculated by density functional theory in the PBE/TZVP version. The conformer of symmetry S4v (D2d) had the lowest energy. Nonplanar diazepine rings induced small but perceptible out-of-plane distortions in the central porphyrazine ring of MgPADz4Ph8. This feature correlated with the observed Stokes shifts of 400 and 350 cm–1 (at 293 K) for MgPADz4Ph8′ and ZnPADz4Ph8′ whereas the metal phthalocyanines had shifts of ~50 cm–1. Excited electronic states of MgPADz4Ph8 were calculated using INDO/Sm. The Q-state energy of 15,200 cm–1 agreed well with the observed value of 14,800 cm–1. Strong featureless absorption in the range 330–450 nm (Soret band analog) with maxima at ~25,000 and ~29,000 cm–1 was due mainly to two strong electronic transitions with calculated energies of 24,100 and 31,500 cm–1; a shoulder on the long-wavelength side of the Soret band at ~23,000 cm–1, to a transition of calculated energy 23,800 cm–1. [ABSTRACT FROM AUTHOR]

Glasses and glass-ceramics with nominal composition 73 TeO 2 – 4BaO– 3Bi 2 O 3 –18SrF 2 -2RE 2 O 3 (where RE = Eu, Dy) have been synthesized by conventional melt-quenching technique and subsequent heat treatment at 370 °C for 24 h in air atmosphere. Various Eu3+ to Dy3+ molar ratio have been applied to investigate luminescence properties in both glass and glass-ceramic matrices. Especially, white light emission through simultaneous excitation of Eu3+ and Dy3+ has been studied in detail. Influence of crystalline SrF 2 phase on luminescence kinetics has been determined by luminescence decay time measurements. Presence of crystalline SrF 2 phase has been confirmed by X-ray diffraction technique XRD and transmission electron microscopy TEM. X-ray photoelectron spectroscopy XPS and Fourier-transform infrared spectroscopy FTIR have been applied to get further insight into structural properties of glass and glass-ceramic materials. Color tunable white light emission has been obtained using UV excitation. Influence of the SrF 2 crystallization on luminescence properties of prepared materials have been described in detail. Moreover, luminescence properties and especially emission color dependence on the Eu3+ to Dy3+ molar ratio have been exhaustively studied. Color-tunable white light emission has been observed as a result of simultaneous radiative transition of both, Eu3+ and Dy3+ ions when applying UV excitation. Judd – Ofelt and other optical parameters have been calculated based on luminescence emission spectra. Achieved results confirm that tellurite glass-ceramics containing SrF 2 nanocrystals are good hosts for RE3+ ions and they can be considered as new phosphors for white light emitting diodes WLEDs. • Transparent oxyfluoride glass-ceramics with SrF 2 nanocrystals have been prepared. • Color-tunable white light emission has been obtained by adjusting Eu3+/Dy3+ molar ratio. • SrF 2 crystallization influence onto luminescence of Eu3+ and Dy3+ has been studied. • Judd-Ofelt parameters have been calculated using JOES application software. [ABSTRACT FROM AUTHOR]

Abstract The thermal and optical properties of oxyfluorotellurite (65-x)TeO 2 -20ZnF 2 -12PbO-3Nb 2 O 5 -xSm 2 O 3 (x = 0.5, 2 and 5) glass systems were investigated. Glass thermal stability were monitored by differential thermal analysis (DTA) and adequate thermal stability criteria ΔT, H' and S were determined. It was shown that the thermal stability of the investigated materials increases with the increasing of samarium ions content. The absorption and emission spectra of Sm3+ ions in oxyfluorotellurite glass were recorded in the wide spectral range from UV to NIR. Based on the Judd-Ofelt (J–O) procedure oscillator strengths, phenomenological Judd-Ofelt intensity parameters Ω 2,4,6, radiative transition probabilities, branching ratios and radiative lifetimes of luminescent levels were determined. The luminescence decay curves of the 4G 5/2 (Sm3+) excited state were recorded for three different concentrations of Sm3+ and corresponding experimental lifetimes were determined. Photoluminescence emission spectra were measured in the temperature range from 300 K up to 725 K to evaluate the materials under study as luminescent temperature sensor. Highlights • (65-x)TeO2-20ZnF2-12PbO-3Nb2O5-xSm2O3 (x = 0.5, 2, 5 mol%) glasses were prepared. • Thermal properties of glasses were analyzed as a function the Sm3+ concentrations. • The optical properties of Sm3+ ions in oxyfluorotellurite glass were assessed. • The materials under study were evaluated as luminescent temperature sensors. [ABSTRACT FROM AUTHOR]

Abstract A series of different Eu3+ ions incorporated La 2 Mo 2 O 9 phosphors exhibiting photoluminescence (PL) peaks in the red region (613 nm; 5D 0 →7F 2) were successfully synthesized by a citrate sol-gel method. Under the 351 nm excitation, the optimal doping concentration of Eu3+ ions was identified to be 25 mol% with higher PL emission intensity and further the concentration quenching mechanism was governed by electric diploe-diploe interaction. More importantly, the optimized phosphor was demonstrated high color purity while the Commission Internationale de I'Eclairage chromaticity coordinates were (0.661, 0.339). The intrinsic radiative transition lifetime for the optimized red phosphor was calculated to be 530.7 μs and the local structure environment of Eu3+ ions in the La 2 Mo 2 O 9 host matrix was also analyzed by the Judd-Ofelt theory. Moreover, a red-emitting light-emitting diode (LED) device was fabricated by combing a near-ultraviolet LED chip with the optimized red phosphor, which exhibits a dazzling red light. Based on the obtained results, the Eu3+ ions activated La 2 Mo 2 O 9 phosphors are expected to be as a promising red-emitting phosphor for solid-state lighting. Graphical abstract Image 1 Highlights • A series of La 2 Mo 2 O 9 :Eu3+ phosphors were synthesized by a facile sol-gel method. • All the samples emitted bright red emissions from the Eu3+ ions pumped by 351 nm light. • Optimized phosphors had high color purity of 96.3% while CIE values were (0.661, 0.339). • The refractive index was 2.48 while the Ω 2 and Ω 4 were obtained by Judd-Ofelt theory. [ABSTRACT FROM AUTHOR]

The high phonon energy and short infrared cut-off wavelength of conventional oxide glass (or crystal) hosts are the limitations to achieve mid-infrared (MIR, λ≥2.5μm) luminescence. In present study, the luminescence performance of low phonon and non-conventional TeO2-TiO2-La2O3-based glass (TTL) host doped with Ho3+ and Ho3+/Yb3+ has been investigated, for visible to MIR range. The MIR emission band with peak at 2.88μm (Ho3+:5I6→5I7) and NIR band at 2.04μm (Ho3+:5I7→5I8) has been realized from Ho3+ singly doped TTL glass due to low phonon energy and extended transmission window of the host. Intensity of MIR and NIR emission bands have enhanced significantly in Ho3+/Yb3+: TTL glass under Yb3+ excitation, signifying an efficient Yb3+→Ho3+ energy transfer. The Judd-Ofelt analysis, on Ho3+ absorption characteristics reveals relatively better radiative transition probability (34.4s−1) and branching ratio (10.5%), which is associated to Ho3+:5I6→5I7 transition. The effective bandwidth of 2.88μm emission band is 180nm, with stimulated emission cross-section is 4.26×10-21cm2 and its gain bandwidth has been evaluated as 7.67×10-26cm3. For 2.04μm (Ho3+:5I7→5I8) emission band, the effective bandwidth of 160.5nm and gain bandwidth of 7.26×10-26cm3 have been accomplished. The non-resonant Förster-Dexter method has been applied to Ho3+/Yb3+: TTL glass on emission (donor, Yb3+) and absorption (acceptor, Ho3+) cross sections. The evaluated donor-donor (CDD) and donor-acceptor (CDA) energy transfer micro-parameters are 1.02×10-38 and 5.88×10-41cm6/s respectively while, maximum energy transfer efficiency has been 80%. In concise, Ho3+/Yb3+ codoped TeO2–TiO2–La2O3 glass host has revealed its potential for MIR to NIR photonic applications. [ABSTRACT FROM AUTHOR]

Experimental luminescence and selective-emission (SE) spectra of YAG:Er3+ (10 at.%) and CaF2:Er3+ (1 at.%) single crystals and Er2O3 polycrystal under laser and laser thermal excitation of the Er3+-ion multiplets are compared. Luminescence spectra under resonant excitation are determined by multiplet population relaxation with the corresponding radiative and nonradiative probabilities. The form of the SE spectra is determined by the thermal population of the multiplets and the probabilities of only radiative transitions. The SE band at 800 nm (4I9/2 → 4I15/2) is an indicator of high-temperature thermal emission of Er3+ ions. The absence of this band in luminescence spectra is explained by the short lifetime of the τ(4I9/2) level of 53 ns at T = 300 K. [ABSTRACT FROM AUTHOR]

In this article, Dy 3+ doped and K + co-doped BaWO 4 phosphors were synthesized by a solid state reaction method and the effect of Dy 3+ /K + doping/co-doping concentration on the structural and photoluminescence (PL) properties were investigated. Rietveld refinement analysis revealed the tetragonal structure of the phosphors and lattice parameter contraction/expansion due to doping/co-doping. The energy band gap reduced with the increasing doping and co-doping concentration in the host materials. Judd-Ofelt (J-O) parameters were calculated from the excitation spectra. J-O parameters described the covalency dependency on the environment around the Dy 3+ ion in the lattice. Intense white light was achieved by Dy 3+ doping. The PL concentration quenching mechanism was described and the suggested quenching mechanism was dipole-dipole interactions. K + co-doping with Dy 3+ doping suggested that charge compensation improved the colour point and increased the internal quantum efficiency from 56 to 67% owing to a reduction in the non-radiative transitions which was proven by using the J-O theory. A short life time (281.60 μs) and CCT value (5392 K) very close to day light of the Ba 1-x-y Dy x K y WO 4 (x = 0.10; y = 0.05) indicated the suitability of the tungstate based phosphors for white light emitting diode applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Red emissive complexes with [Eu(TFFB) 3 L] stoichiometry were synthesized and investigated by spectroscopic studies. • Red emissive behavior of the complexes was characterized by photoluminescence study. • Photophysical characteristics of the mononuclear Eu(III) complexes were analyzed theoretically (JOES) and experimentally. • Probability amplitude distribution and the energy of HOMO and LUMO were estimated through DFT. Heteroleptic trivalent complexes of europium were prepared on reaction of EuCl 3 ·6H 2 O, fluorinated 1,3-diketone and 2,2′-bipyridine or its derivatives in the molar ratio of 1:3:1 respectively. Structural analysis of prepared complexes was done via spectral study. Luminescence features of synthesized complexes have been explored by the photoluminescence and decay spectral profile. Strong emission in the red spectral region was observed for Eu3+ ion corresponding to the electric dipole 5D 0 → 7F 2 hypersensitive transition. The radiative transition probabilities as well as the Judd-Ofelt parameters were computed and discussed. Complexes emit red light in the visible spectrum as illustrated by their CIE color coordinates are essential for creating effective display and lighting devices. [ABSTRACT FROM AUTHOR]

The Λ b 0 → Λ ϕ decay is observed using data corresponding to an integrated luminosity of 3.0 fb − 1 recorded by the LHCb experiment. The decay proceeds at leading order via a b → s s ‾ s loop transition and is therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of 5.9 standard deviations. The value of the branching fraction is measured to be ( 5.18 ± 1.04 ± 0.35 − 0.62 + 0.67 ) × 10 − 6 , where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero. [ABSTRACT FROM AUTHOR]

YO:Eu phosphor was deposited on quartz fibers by electron beam evaporation technology and the deposited fibers were then annealed at different rates from 1 to 10 °C/min. Particle shape of the YO:Eu deposited on fibers was changed with the increased annealing rate and the particle size was increased significantly with the rise of annealing rate to 5 °C/min. The deposited film on fibers exhibited a well cubic phase after annealing treatment and its crystallization was obviously enhanced with the increased rate. The luminescent properties of the films were markedly improved by annealing treatment and the emission intensity was increased as the rate elevated from 1 to 10 °C/min because of the increased radiative transition probability of the Eu ions. The CIE chromaticity coordinates results indicated that the films can display improved color purity of red emission after annealing treatment and the color purity of the annealed films was gradually improved as the increased treating rate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Samarium doped langatate crystal was grown by Czochralski method. [•] Thermal dependences of Sm3+ emission and absorption have been measured. [•] Judd–Ofelt analysis was carried out and radiative transition rates were calculated. [•] Inhomogeneous broadening of spectral lines has been observed. [ABSTRACT FROM AUTHOR]

• NIR-NIR luminescence thermometry via the phonon-assisted energy transfer from Yb3+ to Nd3+ was developed. • Luminescence thermometry properties were modulated by engineering host matrix with SiO 2. • Ultra-high sensitivity and resolution were achieved within a wide temperature scope. Luminescence thermometry based on the rare earth (RE) doped materials has displayed promising applications in various fields due to its fast response and high spatial resolution. However, the achievement of sensitive and accurate temperature sensing over a wide temperature scope is still a great challenge for this thermal sensing technology. Herein, excited by 980 nm laser, the inverse thermal responses of the near-infrared emissions in Nd3+-Yb3+ codoped phosphors, which was attributed to the phonon-assisted energy transfer between RE ions, were employed for ratiometric thermometry within the temperature range of 303–773 K. The modification of thermometric capability for the NIR luminescence was proposed through engineering the aluminate host matrix with SiO 2. The influence of SiO 2 on the luminescence behaviors of Nd3+ and Yb3+ was systematically investigated through the X-ray diffraction patterns, Fourier-transform infrared spectra, Judd-Ofelt theory calculation, as well as luminescence decay profiles. The results demonstrated that the luminescence and the subsequent thermal sensing properties of Nd3+-Yb3+ ion pair were strongly dependent on the host. As the host structure varied from aluminate to aluminosilicate, the spontaneous radiative transition and the energy transfer for RE ions were clearly improved, whereas the multiphonon nonradiative relaxations were weakened. The Nd3+-Yb3+ codoped aluminosilicate phosphors synthesised by adding 100 mol% SiO 2 exhibited much high sensitivity (0.7–4.6% K−1) at temperatures ranging from 303 to 773 K, accompanied with a measurement uncertainty of about 0.1 K. This work provides an effective guidance for developing high-performance luminescence-based ratiometric thermometers. [ABSTRACT FROM AUTHOR]

Luminescence spectra of CaPrF solid solutions are studied. It is found that, depending on the excitation energy, different kinds of emission centers appear in these spectra. An interconfigurational 4f 5d →4f luminescence is typical for single Pr ions in tetragonal sites. Data on the structure of the solid solutions show that the emission centers involved in S → 4f transitions can be attributed to Pr ions contained in clusters. [ABSTRACT FROM AUTHOR]

We have decomposed light-emitting diode (LED) current into component currents by identifying the ideality factor of each component and by fitting the measured and simulated current–voltage ( I–V ), I(dV/dI)-I and the shape of the relative luminescence efficiency–current characteristics. Nearly unity ideality factor of the radiative recombination current is found from luminescence–voltage (L– V) characteristics in AlGaInP red and GaInN green and blue LEDs. The current-component analysis enables an estimation of the internal quantum efficiency (IQE) as a function of current. Compared with red LEDs, blue LEDs suffer from lower radiative recombination efficiency and much larger efficiency droop to result in lower IQE. [ABSTRACT FROM PUBLISHER]

Abstract: Dy3+ doped boro-tellurite glasses were prepared by following melt quenching technique with the chemical composition (69− x)H3BO3 + xTeO2 +15Mg2CO3 +15K2CO3 +1Dy2O3 (where x =0, 10, 20, 30 and 40wt%) by varying the tellurium dioxide content. The structural and optical properties have been studied through XRD, FTIR, absorption, luminescence and decay time measurements. The XRD pattern has been used to confirm the amorphous nature of the prepared glasses. The FTIR spectra reveals the presence of B–O vibrations and Te–O stretching modes of TeO3 and TeO6 units in the prepared glasses. The UV–vis–NIR absorption spectra were used to calculate the oscillator strength, bonding parameters ( and δ) and Judd–Ofelt intensity parameters (Ω λ , λ =2, 4 and 6). The radiative transition probability (A), stimulated emission cross section and the experimental, calculated branching ratios (β R) have been calculated from the luminescence spectra corresponding to 4F9/2 → 6H11/2, 6H13/2, and 6H15/2 excited state transitions. The structural and optical properties corresponding to the compositional changes were discussed and compared with the similar studies. [Copyright &y& Elsevier]

The luminescence of Cu+ and Cu2+ ions in CsBr:Cu and CsBr:CuBr2 crystals, respectively, is investigated under excitation by synchrotron radiation in the CsBr fundamental absorption range at 10 K and 300 K. The existence of the luminescence bands of different origin: (i) the intrinsic radiative transition of Cu+ ions in the bands peaked at 2.61 eV and 2.23 eV, (ii) the recombination luminescence of Cu2+ ions in the bands peaked at 2.55 eV and 2.13 eV, (iii) the luminescence of excitons localized around Cu+ and Cu2+ ions in the band peaked at 3.08 eV and 3.38 eV, respectively, was found in CsBr:Cu and CsBr:CuBr2 crystals. The energies of creation of exciton localized around Cu+ and Cu2+ ions (6.06 eV and 6.09 eV, respectively, at 10 K) and excitons bound with these ions (5.83 eV and 5.99 eV at 300 K) were determined as well. [ABSTRACT FROM AUTHOR]

• Sensitized Mn2+ luminescence is studied in lithium tetraborate. • Existence of complex luminescence centres is proposed. • Slow or ultrafast Mn2+ luminescence decays occur depending on the excitation energy. • Mechanisms for excitation transfer and luminescence decay acceleration are proposed. Sub-nanosecond luminescence of Mn2+ in Mn-, Sn/Mn-, and Cu/Mn-doped Li 2 B 4 O 7 ceramics is observed under laser excitation. Picosecond pulsed laser radiation (350–370 nm) generates the frequency-doubled radiation directly in a single microcrystal selected in a ceramic sample, with this secondary radiation falling within the impurity-induced VUV excitation bands of doped Li 2 B 4 O 7. These excitation bands are attributed to the creation of an impurity-bound intra-anionic exciton in Me i O 4 –BO 3 –Mn Li complex centres (Me i = Mn, Sn, or Cu). The exciton, in turn, interacts with a nearby Mn2+ ion due to mixing of the Mn2+ excited states with the excitonic states. Exciton annihilation involves Mn2+ energy levels as transient states and causes a sub-nanosecond radiative transition which is accelerated, being accompanied by rearrangement of the surrounding atoms. Excitation within the lower-energy bands is related to the other part of the complex luminescence centre, this is metal-to-ligand intra-anionic charge transfer, which makes an electron accessible to Mn Li , while the hole is transferred only during relaxation of the excited structure. Mn2+ radiative transitions are not forced in the latter case, and slow Mn2+ luminescence decay is observed. [ABSTRACT FROM AUTHOR]

The absorption, emission spectra and lifetime of the 4F9/2 fluorescent level of Dy3+ in YAl3(BO3)4 crystal were investigated. Energy level structure was constructed from absorption and emission spectra recorded at 5 K. The measured oscillator strengths of the transitions between the J manifolds at 300 K were compared with those derived from the Judd–Ofelt theory. The radiative transition rates and radiative lifetimes were calculated. Although there are several transitions originating in the 4F9/2 level a major part of emission intensity is contained in the 4F9/2→6H13/2 transition. Measurement of selfquenching of the 4F9/2 luminescence provided a parameter characterizing an activator–activator interaction, which may be used to predict an optimal Dy3+ concentration. The narrow and polarization dependent emission lines, relatively long lifetime of the 4F9/2 metastable level (τ=520 μs) and its high quantum efficiency are advantageous for low threshold laser action in both CW and pulsed operation. The emission cross-section of a potential laser line at 570 nm connected with 4F9/2→6H13/2 transition was estimated. [Copyright &y& Elsevier]

TiO2 nanoparticles doped with different amounts of Nd3+ (0.5, 1, and 3 wt.%) were synthetized by the sol–gel method, and evaluated as potential temperature nanoprobes using the fluorescence intensity ratio between thermal-sensitive radiative transitions of the Nd3+. XRD characterization identified the anatase phase in all the doped samples. The morphology of the nanoparticles was observed with SEM, TEM and HRTEM microscopies. The relative amount of Nd3+ in TiO2 was obtained by EDXS, and the oxidation state of titanium and neodymium was investigated via XPS and NEXAFS, respectively. Nd3+ was present in all the samples, unlike titanium, where besides Ti4+, a significantly amount of Ti3+ was observed; the relative concentration of Ti3+ increased as the amount of Nd3+ in the TiO2 nanoparticles increased. The photoluminescence of the synthetized nanoparticles was investigated, with excitation wavelengths of 350, 514 and 600 nm. The emission intensity of the broad band that was associated with the presence of defects in the TiO2, increased when the concentration of Nd3+ was increased. Using 600 nm for excitation, the 4F7/2→4I9/2, 4F5/2→4I9/2 and 4F3/2→4I9/2 transitions of Nd3+ ions, centered at 760 nm, 821 nm, and 880 nm, respectively, were observed. Finally, the effect of temperature in the photoluminescence intensity of the synthetized nanoparticles was investigated, with an excitation wavelength of 600 nm. The spectra were collected in the 288–348 K range. For increasing temperatures, the emission intensity of the 4F7/2→4I9/2 and 4F5/2→4I9/2 transitions increased significantly, in contrast to the 4F3/2→4I9/2 transition, in which the intensity emission decreased. The fluorescence intensity ratio between the transitions I 821 I 880 = F 5 / 2 4 I 4 9 / 2 F 4 3 / 2 I 4 9 / 2 and I 760 I 880 = F 4 7 / 2 I 4 9 / 2 F 4 3 / 2 I 4 9 / 2 were used to calculate the relative sensitivity of the sensors. The relative sensitivity was near 3% K−1 for I 760 I 880 and near 1% K−1 for I 821 I 880 . [ABSTRACT FROM AUTHOR]

The influence of erbium ion concentration on the optical properties of BaF2:ErF3 crystals was investigated. Four ErF3 concentration (0.05, 0.08, 0.15 and 0.5 mol% ErF3)-doped BaF2 crystals were obtained using the Bridgman technique. Room temperature optical absorption in the 250–850 nm spectral range was measured, and the photoluminescence (PL) and decay times were also investigated. The Judd–Ofelt (JO) approximation was used, taking into account four absorption peaks (at 377, 519, 653 and 802 nm). The JO intensity parameters, Ωt (t = 2, 4, 6), were calculated. The influence of the ErF3 concentration on the JO parameters, branching ratio, radiative transition probability and radiative lifetime were studied. The obtained results were compared with measured values and with those reported in the literature. Under excitation at 380 nm, the well-known green (539 nm) and red (668 nm) emissions were obtained. The calculated and experimental radiative lifetimes were in millisecond range for green and red emissions. The intensity of the PL spectra varied with the Er3+ ion concentration. The emission intensity increased linearly or exponentially, depending on the ErF3 concentration. Under excitation at 290 nm, separate to the green and red emissions, a new UV emission band (at 321 nm) was obtained. Other research has not reported the UV emission or the influence of ErF3 concentration on emission behavior. [ABSTRACT FROM AUTHOR]

Optical absorption spectra and luminescence spectra were recorded as a function of temperature between 295 K and 800 K for single crystal samples of Gd2SiO5:Dy3+, Lu2SiO5:Dy3+, LiNbO3:Dy3+, and Gd3Ga3Al2O12:Dy3+ fabricated by the Czochralski method and of YAl3(BO3)4:Dy3+ fabricated by the top-seeded high temperature solution method. A thermally induced change of fluorescence intensity ratio (FIR) between the 4I15/2→ 6H15/2 and 4F9/2 → 6H15/2 emission bands of Dy3+ was inferred from experimental data. It was found that relative thermal sensitivities SR at 350 K are higher for YAl3(BO3)4:Dy3+ and Lu2SiO5:Dy3+than those for the remaining systems studied. Based on detailed examination of the structural peculiarities of the crystals it was ascertained that the observed difference between thermosensitive features cannot be attributed directly to the dissimilarity of structural factors consisting of the geometry and symmetry of Dy3+ sites, the number of non-equivalent Dy3+ sites, and the host anisotropy. Instead, it was found that a meaningful correlation between relative thermal sensitivity SR and rates of radiative transitions of Dy3+ inferred from the Judd–Ofelt treatment exists. It was concluded that generalization based on the Judd–Ofelt parameters and luminescence branching ratio analysis may be useful during a preliminary assessment of thermosensitive properties of new phosphor materials. [ABSTRACT FROM AUTHOR]

The luminescence properties of novel Eu3+ doped and (Li+,Ni2+) co-doped ZnTiO 3 nanophosphors were reported in this work. The powder samples were fabricated via the facile solution combustion technique. The structural and photoluminescence characteristics of ZnTiO 3 :0.0075Eu3+ nanophosphor are influenced by calcination temperature and co-doped ions. Under the excitation by near UV and blue light, the red luminescence of prepared nanophosphor appeared owing to strong absorption and efficient energy transfer mechanism. In the developed nanophosphors, the enhancement red emission is only possible in the presence of Li+ and Ni2+ ions. Phase transformation in high temperature form of zinc titanate improves the non-radiative transition and co-dopant ions in phase pure defect spinel can increase the rate of radiative transition. The photometric characterizations hint that the nanophosphor materials proved to be highly beneficial for the red light emission in WLEDs applications. • Nanophosphors were synthesized via low cost solution combustion method. • Role of calcination temperature and various co-dopant has been studied. • Co-dopant shift the excitation from NUV to blue region. • Nanophosphor under blue excitation can be used as a promising candidate in WLEDs. [ABSTRACT FROM AUTHOR]

Ratiometric luminescence thermometry employing luminescence within the biological transparency windows provides high potential for biothermal imaging. Nd3+ is a promising candidate for that purpose due to its intense radiative transitions within biological windows (BWs) I and II and the simultaneous efficient excitability within BW I. This makes Nd3+ almost unique among all lanthanides. Typically, emission from the two 4F3/2 crystal field levels is used for thermometry but the small ~100 cm−1 energy separation limits the sensitivity. A higher sensitivity for physiological temperatures is possible using the luminescence intensity ratio (LIR) of the emissive transitions from the 4F5/2 and 4F3/2 excited spin-orbit levels. Herein, we demonstrate and discuss various pitfalls that can occur in Boltzmann thermometry if this particular LIR is used for physiological temperature sensing. Both microcrystalline, dilute (0.1%) Nd3+-doped LaPO4 and LaPO4: x% Nd3+ (x = 2, 5, 10, 25, 100) nanocrystals serve as an illustrative example. Besides structural and optical characterization of those luminescent thermometers, the impact and consequences of the Nd3+ concentration on their luminescence and performance as Boltzmann-based thermometers are analyzed. For low Nd3+ concentrations, Boltzmann equilibrium starts just around 300 K. At higher Nd3+ concentrations, cross-relaxation processes enhance the decay rates of the 4F3/2 and 4F5/2 levels making the decay faster than the equilibration rates between the levels. It is shown that the onset of the useful temperature sensing range shifts to higher temperatures, even above ~ 450 K for Nd concentrations over 5%. A microscopic explanation for pitfalls in Boltzmann thermometry with Nd3+ is finally given and guidelines for the usability of this lanthanide ion in the field of physiological temperature sensing are elaborated. Insight in competition between thermal coupling through non-radiative transitions and population decay through cross-relaxation of the 4F5/2 and 4F3/2 spin-orbit levels of Nd3+ makes it possible to tailor the thermometric performance of Nd3+ to enable physiological temperature sensing. [ABSTRACT FROM AUTHOR]

Eu3+-doped CaF 2 nanocubes with variable europium concentration, [Eu3+] = 0, 0.6, 1.3, 1.7, 2.2 and 5.4 mol%, have been synthesized by a direct precipitation route. It has been found that, within this concentration range, the nanoparticles present the fluoride-type crystalline structure and the characteristic cubic shape of CaF 2 crystals. The nanoparticle size follows a log-normal distribution with a mean value decreasing with the Eu3+ content. Rietveld refinement has been performed to calculate the lattice parameter and crystallite size. Eu3+ concentration affects both parameters giving rise to an increase in the lattice parameter and a reduction of crystallite size. The luminescent properties of Eu3+ ions in these nanostructures have been investigated under CW and pulsed excitation. A Judd-Ofelt analysis, as function of the Eu3+ content, has been performed to determine the transition probabilities, radiative lifetimes and branching ratios of the 5D 0 emitting level. It was found that Ω 2 and Ω 4 Judd-Ofelt intensity parameters are dependent on the doping level, showing an evolution that indicates a decrease in the Eu3+ site local symmetry with increasing Eu3+ concentration. Finally, it has been observed that the characteristic luminescence decay time of the 5D 0 manifold is reduced with increasing Eu3+ concentration. This effect is partially due to an increase of radiative transition probability, associated with a reduction in the local symmetry of the lanthanide ions, and also to the occurrence of concentration quenching effects. Image 1 • High CaF 2 :Eu3+ nanocubes. • Eu3+ excellent probe to link structural and luminescence properties. • Judd-Ofelt analysis dependent on structural properties. • Optimum doping level at 2 mol% europium concentration. [ABSTRACT FROM AUTHOR]