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Relativistic coupled-cluster calculations of the ionization potential, dissociation energy, and excited electronic states under 35 000 cm−1 are presented for the actinium monofluoride (AcF) molecule. The ionization potential is calculated to be IPe = 48 866 cm−1, and the ground state is confirmed to be a closed-shell singlet and thus strongly sensitive to the T , P -violating nuclear Schiff moment of the Ac nucleus. Radiative properties and transition dipole moments from the ground state are identified for several excited states, achieving a mean uncertainty estimate of ∼450 cm−1 for the excitation energies. For higher-lying states that are not directly accessible from the ground state, possible two-step excitation pathways are proposed. The calculated branching ratios and Franck–Condon factors are used to investigate the suitability of AcF for direct laser cooling. The lifetime of the metastable (1)3Δ1 state, which can be used in experimental searches of the electric dipole moment of the electron, is estimated to be of order 1 ms. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analysis of emission in erbium-doped and erbium and ytterbium co-doped fluoroindate glasses has been presented. The luminescence of the erbium transitions and the effect of ytterbium co-doping under 488, 808 and 976 nm laser excitation have been discussed. Optimization of rare-earth (RE) ions doping concentration and the energy transfer processes related to the sensibilization effect in Er3+/Yb3+ co-doped fluoroindate glasses focusing on the reciprocal distribution of radiative transitions, energy transfer parameters, and lifetimes have been analyzed. The luminescence consists of several bands in the visible (525, 546 and 660 nm) and the infrared (1550 and 2700 nm) spectral regions that correspond to characteristic radiative energy transitions within the erbium ions. In glasses co-doped with the Er3+/Yb3+ system, an augmentation in the emission intensity was observed in the visible and at 1550 nm, while a decrease was observed in the 2700 nm infrared band. The increase of the Yb3+: 2F 5/2 lifetime under 488, 808 and 976 nm excitation showed significant Er3+: 4I 11/2 → Yb3+: 2F 5/2 back energy transfer. Based on the analysis of the available literature, it can be concluded that energy transfer upconversion and cooperative energy upconversion play a significant role in modulating luminescence intensity values within the examined emission bands. This effect is likely enhanced due to the incorporation in a low phonon energy glass matrix. As a result of the above optimization, a glass optical fiber co-doped with 0.8 YbF 3 /1.4 ErF 3 (in mol%) was drawn and characterized, showing a strong emission at 2.77 μm. The optimized Er3+/Yb3+ co-doped fluoroindate glass and glass optical fiber confirmed their ability to be used in the visible and near-infrared spectral regions as efficient optical fiber sources. [ABSTRACT FROM AUTHOR]

Thermal disturbance deteriorates the radiative transitions of up‐conversion phosphor, leading to decreased emission intensity at high operation temperatures. In this work, a thermal‐favored Yb3+/Nd3+ co‐doped KGaGeO4 up‐conversion phosphor with a negative thermal quenching behavior is explored. The as‐developed phosphor performs a one‐photon anti‐Stokes emission and exhibits a remarkable enhancement for the rise of ambient temperature reaching 653 K. It is demonstrated that the fascinating thermal behavior of the up‐conversion procedure is attributed to the enhanced energy transfer from the corresponding sensitizers to the activators by phonon assistance. Moreover, the microscopic dynamical process of phonon assistance and annihilation is revealed by introducing Er3+ ions as a probe. These results not only shed light on the phonon‐assisted strategy to build a highly efficient anti‐Stokes emission system but also open prospects for constructing phonon‐favored transitions with nonthermally coupled emissions to realize luminescence thermometry for their distinct thermal responsivity. [ABSTRACT FROM AUTHOR]

A novel vanadate host Ca2LiMg2V3O12 (CLMV) and the Eu3+‐doped samples were synthesized via a solid‐state reaction method. The phase formation and the morphological analysis were studied in detail. The Rietveld refinement result shows that the host belongs to cubic space group Ia‐3d (230) with lattice parameter, a = 12.3948 Å, V = 1904.23 Å3, and Z = 8. The diffuse reflectance spectroscopy measurement estimated the bandgap of the host and the CLMV:0.05Eu3+ phosphors. The host exhibits a broad absorption band (peak at 345 nm) ranging from 240 to 380 nm, which is attributed to the charge transfer in the O2−–V5+ complex. Under near UV excitation (λexc = 345 nm), the host gives a broad emission band covering the visible region from 400 to 730 nm and the emission is in the bluish–green region of the CIE diagram. When the host is doped with the Eu3+ ions and excited at 345 nm, the emission spectrum depicts the superimposition of the characteristic emission bands (red emission) of the Eu3+ ions corresponding to the f–f transitions over the broad emission band of the host. The calculated color coordinates (9600 to 2280 K) demonstrated the color tuning ability of the phosphor as the dopant concentration is increased in the host. This is because the VO43− group plays the sensitiser role and partially transfers energy with the Eu3+ ions. When the same set of phosphors were excited at the dominant characteristic excitation band (λexc = 394 nm) of the Eu3+, the characteristic emission bands of the Eu3+ in the orange–red region were observed. As the electric dipole transition of the Eu3+ was found to be dominant, the prepared phosphors possessed high color purity (CP). The energy transfer mechanism and the lifetime values were also presented. The temperature‐dependent PL studies showed good thermal stability of the optimum sample. Various radiative transition properties were analyzed by the Judd–Ofelt theory. The photometric results reveal the color tuning ability and CP of the CLMV:xEu3+ phosphors. [ABSTRACT FROM AUTHOR]

Wide‐coverage near infrared (NIR) phosphor‐converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide‐coverage NIR phosphors. Here, we report the single‐component lanthanide (Ln3+) ions doped Cs2M(In0.95Sb0.05)Cl6 (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd‐Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs2M(In1−xSbx)Cl6 NCs can break the forbidden of f‐f transition of Ln3+, thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln3+. Finally, the wide‐coverage NIR LEDs based on Sm3+, Nd3+, Er3+‐tridoped Cs2K0.5Rb0.5(In0.95Sb0.05)Cl6 NCs are fabricated and employed in the multiplex gas sensing and night‐vision application. [ABSTRACT FROM AUTHOR]

Wide‐coverage near infrared (NIR) phosphor‐converted LEDs possess promising potential for practical applications, but little is developed towards the efficient and wide‐coverage NIR phosphors. Here, we report the single‐component lanthanide (Ln3+) ions doped Cs2M(In0.95Sb0.05)Cl6 (M=alkali metal) nanocrystals (NCs), exhibiting emission from 850 to 1650 nm with high photoluminescence quantum yield of 20.3 %, which is accomplished by shaping the multiple metal halide octahedra of double perovskite via the simple alkali metal substitution. From Judd‐Ofelt theoretical calculation and spectroscopic investigations, the shaping of metal halide octahedra in Cs2M(In1−xSbx)Cl6 NCs can break the forbidden of f‐f transition of Ln3+, thus increasing their radiative transition rates and simultaneously boosting the energy transfer efficiency from host to Ln3+. Finally, the wide‐coverage NIR LEDs based on Sm3+, Nd3+, Er3+‐tridoped Cs2K0.5Rb0.5(In0.95Sb0.05)Cl6 NCs are fabricated and employed in the multiplex gas sensing and night‐vision application. [ABSTRACT FROM AUTHOR]

A series of Eu3+ and Eu3+/Gd3+ co-doped barium-bismuth-borate (Ba–Bi–B) glasses were prepared by melt-quench technique. And deliberated the physical, structural, and spectroscopic properties of all glasses and explored the energy transfer process from Gd3+ to Eu3+ ions. The density of glasses increased with increasing of Gd3+ concentration in co-doped glasses. Characteristics of steady-state and time-resolved photoluminescence (PL) of Eu-doped and Eu3+-Gd3+ co-doped glasses under different excitation wavelengths suggested the prospects of the investigated glass system for display device applications. PL spectrum displays a strong red emission peak centered at 612 nm due to the Eu3+: 5D 0 → 7F 2 transition. Less intense emissions centered at 577 nm (7F 0), 590 nm (7F 1), 651 nm (7F 3) and 700 nm (7F 4) are also observed from the radiative transitions of the excited state 5D 0 of Eu3+ions. The values of radiative parameters such as transition probability, branching ratios, and stimulated emission cross-sections were obtained from Judd–Ofelt theory analysis and indicated the aptness of the Ba–Bi–B glasses for optical devices. A 5-fold enhancement in the PL intensity was observed in 1.0 mol% Eu3+ and 3.0 mol% Gd3+ co-doped glass under λ Exci. = 394 nm excitation. The calculated commission Internationale de l'eclairage color coordinates and correlated color temperature values show that the Ba–Bi–B glasses are useful for red-laser and display device applications. [ABSTRACT FROM AUTHOR]

ZnO–P 2 O 5 glasses activated with Ag m n + clusters and Mn2+ ions were successfully synthetized by the melt-quenching method. X-ray diffraction patterns confirmed the glassy nature for doping concentrations up to 3.0 and 5.0 mol% of Ag+ and Mn2+ ions, respectively, whereas the Raman spectra in all cases displayed δ(P–O–P), ν s (P–O–P), ν s (PO 2) and ν as (PO 2) vibrational modes, typical of a phosphate glass network. The emission spectra under 345 nm (Ag m n + : S 0 → S 1 and Mn2+: 6A 1 (S) → 4T 1 (P) + 4E(D)), 385 nm (Ag m n + : S 0 → S 1) and 407 nm (Mn2+: 6A 1 (S) → 4A 1 (G) + 4E(G) and Ag m n + : S 0 → S 1) excitations, showed the broad band related to the superimposed Ag m n + cluster: S 1 → S 0 , T 2 → S 0 and T 1 → S 0 radiative transitions along with the Mn2+: 4T 1 (G) → 6A 1 (S) one. Under 385 nm excitation, the Mn2+ emission transition is attained by energy transfer from Ag m n + clusters. Such excitations lead to emission tonalities in the bluish white to cold white (345 and 385 nm) and cold white to reddish orange (407 nm) ranges, with correlated color temperature (CCT) values in the 10,095-5371 K (345 nm), 14,768-6862 K (385 nm) and 8592-1633 K (407 nm) ranges. Purplish pink emissions upon 345 nm excitation were obtained as well. The white color tonalities together with the color rendering index (CRI) and absolute quantum yield (QY, external) values up to 95 Ra and 35%, respectively, revealed promissory features for rare-earth-free white light emitting diode applications. The Ag m n + cluster: S 1 → S 0 emission fitting by the Burstein model suggested that the non-radiative energy transfer is mainly mediated by an electric dipole-dipole interaction. [ABSTRACT FROM AUTHOR]

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. [ABSTRACT FROM AUTHOR]

Here we report a new strategy to tune both excitation and emission peaks of upconversion nanoparticles (UCNPs) into the first infrared biowindow (NIR‐I, 650–900 nm) with high NIR‐I‐to‐NIR‐I upconversion efficiency. By introducing the sensitizer Nd3+, activator Er3+, energy migrator Yb3+ and energy manipulator Mn2+ into specific region to construct proposed energy migration processes in the designed core–shell–shell nanoarchitecture, back energy transfer (BET) from activator to sensitizer or migrator can be greatly blocked and the NIR‐to‐red upconversion emission can be efficiently promoted. Consequently, BET‐induced photon quenching and the undesired green‐emitting radiative transition are entirely eliminated, leading to high‐efficiency single‐band red upconversion emission upon 808 nm NIR‐I laser excitation. Our findings provide insights into fundamental lanthanide interactions and advance the development of UCNPs for bioapplications with techniques that overturn traditional limitations. [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]

Near-infrared (NIR) to visible upconversion (UC) luminescence in activator Er3+ and sensitizer Yb3+ codoped systems has been extensively studied. In this work, we report the results of Er3+-sensitized Yb3+ NIR UC emission at ∼1000 nm originating from 2F5/2 → 2F7/2 transition under infrared (IR) excitation at ∼1500 nm responsible for Er3+ 4I15/2 → 4I13/2 transition absorption. The IR to NIR UC is a desirable strategy to increase solar light utilization by reducing the spectral mismatch between the solar spectrum and crystalline silicon (c-Si) solar cells. Er3+ singly doped phosphors are mostly used for realizing the IR to NIR UC emission derived from Er3+ 4I11/2 → 4I15/2 transition centered also at ∼1000 nm. The efficiency of this transition, however, is limited by multiphonon relaxation and radiative transition to the 4I13/2 state. Here, Yb3+ ions are codoped in Y2O3:Er3+, and NIR UC emission with the intensity enhanced 1.5 times is achieved due to efficient energy transfer from Er3+ to Yb3+ and highly efficient Yb3+ emission. The influence of the dopants' concentrations on UC dynamics is studied. The optimal concentration under IR excitation is 5% Er3+ and 1% Yb3+. Our results indicate that introducing Yb3+ ions in Er3+ singly doped phosphors may notably improve the IR to NIR UC performance. [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]

In the classical modeling of decay rates for molecules interacting with a nontrivial environment, it is well known that two alternate approaches exist which include: (1) a mechanical model treating the system as a damped harmonic oscillator driven by the reflected fields from the environment; and (2) a model based on the radiative and nonradiative energy transfers from the excited molecular system to the environment. While the exact equivalence of the two methods is not trivial and has been explicitly demonstrated only for planar geometry, it has been widely taken for granted and applied to other geometries such as in the interaction of the molecule with a spherical particle. Here we provide a rigorous proof of such equivalence for the molecule-sphere problem via a direct calculation of the decay rates adopting each of the two different approaches. [ABSTRACT FROM AUTHOR]

We present a nonperturbative time-dependent quantum mechanical theory of the laser catalysis and control of a bifurcating A+BC↔hω0ABC*(v)↔hω0AB+C reaction, with ABC*(v) denoting an intermediate, electronically excited, complex of ABC in the vth vibrational state. We apply this theory to the low collision energy fermion-boson light-induced exchange reaction, 6Li(2S)+7Li2(3Σu+)↔hω0(6Li7Li7Li)*↔hω06Li7Li(3Σ+)+7Li(2S). We show that at very low collision energies and energetically narrow (∼0.01 cm-1) initial reactant wave packets, it is possible to tune the yield of the exchange reaction from 0 to near-unity (yield >=99%) values. Controllability is somewhat reduced at collisions involving energetically wider (∼1 cm-1) initial reactant wave packets. At these energetic bandwidths, the radiative reactive control, although still impressive, is limited to the 0%–76% reactive-probabilities range. [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 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]

This paper presents three crystallographically and solution NMR (one- and two-dimensional) characterised ternary Ln(iii) complexes, and their photo-physical and opto-electronic properties in the visible and NIR regions. The single crystal X-ray diffraction analysis indicates that the complexes are nona-coordinate with a chemical composition of [Ln(hfaa)3(Hind)3] (hfaa = anion of hexafluoroacetylacetone, Hind = indazole and Ln = Pr, Nd and Sm). The Ln ions, in the complexes, are coordinated to six O-atoms of three hfaa and three N-atoms of three monodentate Hind ligands, making the coordination polyhedra LnO6N3 with distorted monocapped square antiprismatic geometries, low symmetry structures that promote radiative transitions, suggesting efficient energy transfer from the organic ligands to the metal ion. The NMR analysis confirms the nona-coordinate structures and shows the isostructurality of the complexes in solution. The excitation of the complexes at 310 nm led to the characteristic of both visible and near infrared luminescence of the Pr, Nd and Sm complexes. The samarium complex displayed very strong orange-red luminescence. In contrast to the solution, the PMMA doped samples of the complexes showed an enhancement in the emission lifetime and the quantum yield. A triple layered NIR-emitting OLED, fabricated using the Nd-complex as an emitting layer, showed good optical and electrical performances. [ABSTRACT FROM AUTHOR]

Branching ratio measurements for the NO γ bands excited by energy transfer from metastable nitrogen molecules show that the electronic transition moment for the NO(A 2Σ+–X 2Π) transition varies by about 40% over the r-centroid range of 1.13–0.97 Å. Combining this transition-moment variation with radiative lifetime measurements provides a complete set of Einstein coefficients for NO(A–X) transitions from v’=0–2. [ABSTRACT FROM AUTHOR]

A new borate solid solution series of powders, Li 6 Eu 1-x Sm x (BO 3 ) 3 (LSEBx, x = 0.35, 0.5, 0.6, 1), were synthesized by solid-state reaction, characterized and their luminescent properties were investigated. The absorption spectra indicate that absorption takes place mainly from the Sm 3+ 6 H 5/2 ground state, with a strong band at 405 nm. The photoluminescence spectra reveal that the Eu 3+ red emission intensity strongly depends on the Sm 3+ content x. Judd–Ofelt theory was applied to experimental data for the quantitative determination of phenomenological parameters Ωi (i = 2, 4, 6) Judd Ofelt parameters, radiative transition rates and emission quantum efficiency. Owing to the energy transfer from Sm 3+ to Eu 3+ the intense red light detected at 613 nm at room temperature under UV or blue light excitation, was improved by ∼35% as compared with Sm 3+ -free samples. This energy transfer was confirmed by faster decay times of Sm 3+ as energy donors. Moreover, the energy transfer between Sm 3+ and Eu 3+ is unidirectional and irreversible, implying that the energy transfer wastage between Sm 3+ and Eu 3+ is very low. Magnetic susceptibility (χ) measurements of LSEBx were carried out in the temperature range 2–320 K and are used to compare calculated and experimental energy levels. [ABSTRACT FROM AUTHOR]

Quantum cutting (QC) phosphor β - NaYF 4 : Tb 3 + , Yb 3 + nanoparticles (NPs) are decorated with Au nanorods (NRs). By tailoring Au NRs longitudinal plasmon resonance to match the emission wavelength of Yb 3 + ion, plasmon-enhanced near-infrared (NIR) QC luminescence is achieved through improving Yb 3 + ion’s radiative transition rate. The decay curves of Yb 3 + ion in β - NaYF 4 : Tb 3 + , Yb 3 + NPs decorated with Au NRs further confirm the improvement of radiative transition rate. The influence of Au NRs concentration on QC luminescence is also investigated, and the results show that the optimal concentration of Au NRs is 0.12% with the maximum enhancement factor about 3. Our study may not only path the way to achieve simultaneous excitation and emission enhancement of QC luminescence, but also provide a potential application as QC layer to silicon-based solar cells. [ABSTRACT FROM AUTHOR]

A study of the optical, spectral-luminescent and holographic properties of the chlorine-containing photo-thermo-refractive (PTR) glass doped with neodymium ions was carried out. The chlorine-containing PTR glass has been recently produced by replacing the bromine in the standard PTR glass with chlorine. The glass was doped with different concentrations of neodymium ions. The spectroscopic analysis of neodymium in the glass has been performed using the Judd-Ofelt theory based on experimental absorption and emission measurements. Spectroscopic parameters, such as the Judd-Ofelt intensity parameters, radiative and non-radiative transition probabilities, fluorescence lifetimes, stimulated emission cross-sections, and branching ratios, were obtained and found to be comparable with the parameters of the standard PTR glass doped with neodymium. The mechanism of non-radiative energy transfer was analyzed based on the lifetime kinetics measurements. It was found that cross-relaxation among neodymium ions is the dominant non-radiative energy transfer mechanism. Holographic characteristics of the chlorine-containing PTR glasses doped with neodymium have been also studied. The volume Bragg grating was recorded in the doped and undoped glasses. It was found that the UV exposure and heat treatment do not change the spectroscopic characteristics of neodymium ions in the glasses, while the neodymium ions reduce the sensitivity of the glass. The energy transfer from cerium to neodymium when irradiating using the 325-nm laser makes the hologram recording possible on the samples of low neodymium concentrations only. Studying the spectroscopic and holographic properties of the chlorine-containing PTR glass doped with neodymium ions demonstrates the potential of using such a material in the applications of photonics integration and monolithic optical devices like distributed-feedback lasers. • Spectroscopic properties of Nd ions in Cl-PTR glass are comparable to those of Nd in the standard (Br-PTR) glass. • VBG was recorded in the undoped Cl-PTR glass, as well as in the glass doped with Nd. • UV exposure and heat treatment do not affect the spectral-luminescent properties of Nd in the Cl-PTR glass. • Nd reduces the photosensitivity of Cl-PTR due to energy transfer from Ce to Nd during the hologram recording at 325 nm. [ABSTRACT FROM AUTHOR]

Eu3+ ions doped Li 2 O–Al 2 O 3 –Gd 2 O 3 –B 2 O 3 –P 2 O 5 glasses have been prepared by melt quenching and characterized for their physical, optical and luminescence properties. Judd-Ofelt (JO) theory is used to evaluate the oscillator strengths and the three intensity parameters (Ω λ , λ = 2, 4 and 6) of the glasses. The radiative properties such as radiative transition probabilities (A R), radiative lifetimes (τ), branching ratios (β) and emission cross-section (σ e) have been calculated from the absorption spectra according to the JO theory. The scintillation properties of glasses could be measured by comparing emission spectrum under the X-ray induced luminescence with bismuth germanate (BGO). The Commission Internationale de l'Elcairage (CIE) chromaticity coordinates (x,y) were also evaluated from the emission spectra of glasses and values of glasses take part in the red region. • The Eu3+ ions doped Li 2 O–Al 2 O 3 –Gd 2 O 3 –B 2 O 3 –P 2 O 5 glasses fabricated by the melt quenching. • The highest emission intensity is 6.0 mol% of Eu3+ ions. • There is the possible energy transfer from Gd3+ to Eu3+ ion. • The integral scintillation efficiency of Eu 6.0 mol% glass found 24% of BGO scintillator crystal. [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]

This paper investigated the mid-infrared luminescence properties of Er 3+ /Ho 3+ co-doped tellurite germanate glass at 2 μm pumped by 980 nm. Thermal stability of the system, absorption spectra and fluorescence spectra of the Er 3+ /Ho 3+ co-doped glass sample were measured. Besides, the absorption spectra of the Ho 3+ singly doped sample was measured. According to the measured absorption spectra and the Judd–Ofelt theory, the Judd–Ofelt intensity parameters Ω t ( t = 2, 4, 6), spontaneous radiative transition probability, branching ratio and lifetime of Ho 3+ were calculated. And the upconversion emission in Er 3+ doped and Er 3+ /Ho 3+ co-doped tellurite germanate glasses pumped by 980 nm have been investigated. Then the spectroscopic properties and possible energy transfer mechanisms between Ho 3+ and Er 3+ ions were discussed in detail. Meanwhile, the FWHM (146 nm), σ e peak × FWHM (659.92 cm 3 ) and emission cross section (4.52 × 10 −21 cm 2 ) of 5 I 8 → 5 I 7 transition of Ho 3+ were obtained, respectively. The results indicate that Er 3+ /Ho 3+ co-doped tellurite germanate glass is a promising host material for 2 μm solid laser. [ABSTRACT FROM AUTHOR]

Er 3+ /Ce 3+ co-doped and B 2 O 3 modified tellurite glasses with initial composition of TeO 2 –GeO 2 –Li 2 O–Nb 2 O 5 were prepared using melt-quenching technique for potential applications in Er 3+ -doped fiber amplifiers (EDFAs) and lasers. The absorption spectra, fluorescence spectra, up-conversion spectra, Raman spectra and differential scanning calorimeter (DSC) curves of glass samples were measured to evaluate the effect of B 2 O 3 modification on the 1.53 μm band spectroscopic properties of Er 3+ , structural nature and thermal stability of glass hosts. It was shown that the introduction of an appropriate amount of B 2 O 3 oxide can further improve the 1.53 μm band fluorescence emission through an enhanced phonon-assisted energy transfer (ET) from Er 3+ to Ce 3+ ions under the excitation of 980 nm, and the quantitative studies were carried out to elucidate the ET mechanism via calculating the microscopic parameters and phonon contribution ratios. Meanwhile, the thermal stability of glass hosts increases slightly with the introduction of B 2 O 3 oxide. Furthermore, the 1.53 μm band optical signal amplification was simulated based on the rare-earth ion rate and light power propagation equations. An increment in signal gain by about 1.4 dB at 1532 nm was observed in the Er 3+ /Ce 3+ co-doped tellurite glass fiber containing 6 mol% amount of B 2 O 3 oxide, and the maximum signal gain reaches to 31 dB on a 50 cm fiber pumped at 980 nm with power 200 mW. The present results indicate that the prepared Er 3+ /Ce 3+ co-doped tellurite glass modified by an appropriate amount of B 2 O 3 oxide has good prospect as a gain medium applied for 1.53 μm band EDFAs and lasers. [ABSTRACT FROM AUTHOR]

Er 3+ -doped, Er 3+ /Yb 3+ co-doped tellurite glass with and without Ag NPs were synthesized by melt-quenching method. The high resolution transmission electron microscopy (HR-TEM) and selected area electron diffractions (SAED) manifest growth of Ag NPs. The UV–vis–NIR absorption spectroscopy and fluorescence spectroscopy were measured. The optical band gap and multiphonon relaxation rate constants were calculated. The electronic band structure and local density of state (DOS) of Ag NPs are calculated. The fluorescence emission and enhancement mechanism including localized surface plasmon resonance (LSPR) and energy transfer (ET) microcosmic mechanism were discussed. The electric field distributions of Ag NPs are emulated by FDTD solutions software. Local field enhancement (LFE) induced by LSPR and lightning rod effect was found to be responsible for the fluorescence enhancement while energy transfer from Ag NPs to rare-earth was considered ignorable in the samples without photoluminescent emission. [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]

A mechanism of energy transfer sensitization in Eu-doped LiAl 5 O 8 produced by the modified sol-gel method is proposed. The XRD results show the formation of the desired crystalline phase and the solubility limit of Eu dopant. Based in the PL results, a mechanisms of energy transfer (ET) and simultaneous excitation (SE) between the doping ion (Eu3+) and contaminating ions (Cr3+ and Fe3+) were elaborated based in the five possible dynamics. The first attributed to SE between Eu3+- Fe3+ characterized by direct excitation of Eu3+ and Fe3+ ions. The second is attributed to ET between Eu3+-Cr3+, attributed to the radiative transitions 5D 0 →7F 1,2 and Cr3+ ion. Third mechanism is similar to the energy transfer described by the second mechanism in addition to Fe3+ sensitization. The fourth and fifth are due to the SE between Eu3+-Fe3+-Cr3+. • A mechanism of energy transfer sensitization in Eu-doped LiAl 5 O 8 is proposed. • Simultaneous excitation (SE) between the Eu 3+ and contaminating ions (Cr 3+ and Fe 3+ ) were elaborated. • The effects of the Eu 3+ dopant concentration on the structural and optical properties also were investigated. [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]

[Display omitted] • All-TADF WOLEDs with the state-of-the-art power efficiency > 70 lm W−1. • A new spiro host based on 9,9′-spirobi[thioxanthene] core and phosphine oxide group. • Optimized intermolecular interactions for optoelectronic property enhancement. • Synergistic effect of energy transfer and TADF transition in radiation. Host matrix is crucial for optimizing exciton allocation in all Thermally activated delayed fluorescence (TADF) white Organic light-emitting diodes (OLED). However, only few spiro hosts are competent since unbalanced steric and electronic effects. Herein, a new spiro core 9,9′-spirobi[thioxanthene] (ST) based host STDPO is reported, whose two peripheral diphenylphosphine oxide (DPPO) groups are incorporated to construct tridimensional steric hindrance and Intermolecular hydrogen bond (IHB) network. As consequence, STDPO achieves the high enough first triplet (T 1) energy level of 2.93 eV and favorable electron mobility (µ e) by the level of 10−5 cm2 V−1 s−1. Simultaneously, the well-modulated intermolecular interactions in STDPO matrix give rise to the synergistic effect of blue and yellow TADF dopants in exciton utilization. The increased rate constants and efficiencies of radiative transitions and reduced nonradiative rate constants render a photoluminescence quantum yield as high as 90% and 100% exciton utilization efficiency of dually doped white TADF film. STDPO further endowed its single-emissive-layer TADF WOLEDs with the record η PE of 71.8 lm W−1 achieved by spiro hosts. [ABSTRACT FROM AUTHOR]

Most of the mechanoresponsive luminescent (MRL) materials function based on phase transition (crystalline-to-amorphous or crystalline-to-crystalline) or solid-state chemical reaction of the organic solid emitters. However, it is difficult to enable a turn-on type mechanoresponsive luminescence using such strategy. In this work, the defect-induced emission (DIE) of (E)-(4-((2-hydroxy-4-methoxybenzylidene)amino)phenyl)(phenyl) methanone (HMPM) was disclosed, which endows the resulting material with reversible turn-on MRL. The crystalline powder of HMPM is non-emissive, but the emission intensity can be greatly enhanced by external mechanical stimuli, showing high contrast. In the semiquantitative experiment, pressure up to 1.78 N would generate crystal defects, and further induces DIE. Crystallographic data demonstrate that the dark-state stems from the closely-connected plane-style aggregation of neighboring molecules, which allows the intermolecular orbital-overlapping to the disadvantage of radiative transition. Mechanical stimuli would destroy the plane-style aggregation to block intermolecular orbital overlap and the possible energy transfer, resulting in emission-enhancement. Taking advantage of the DIE nature, an information storage film is fabricated, capable of data-writing via mechanical force and data-erasing by fumigation treatment, showing rewritability as well as high signal contrast. [Display omitted] • A D-A luminophore showing defect-induced emission (DIE) is synthesized. • π-orbital overlapping in the closely-connected plane-style aggregation causes emission quenching. • DIE turns on the mechanoresponsive luminescence with reversibility. • The possibility of using DIE material as data storage is analysed. [ABSTRACT FROM AUTHOR]

Abstract: This study presents the luminescent properties of Yb3+/Tm3+ co-dopant ions inside a new host glass based on bismuth germanates. Judd–Ofelt intense parameters, radiative transition rate, radiative lifetime, and branching ratios of Tm3+ in the present glass are calculated based on the absorption spectrum. A strong 1.8μm emission was observed in the Yb3+/Tm3+ co-doped bismuth germanate glass upon the excitation of a conventional 980nm laser diode. Using a spectral overlap model, the micro parameter for direct energy transfer from Yb3+ ions to Tm3+ ions (C DA ) was found to be almost 30 times larger than the back energy transfer from Tm3+ ions to Yb3+ ions (C AD ). The linear dependence of energy transfer probability on the co-dopant concentration exhibits that the energy transfer is assisted by energy migration among donor ions. The large energy transfer efficiency (89%) indicates that the Yb3+/Tm3+ co-doped bismuth germanate glass is a good candidate for the 1.8μm laser. [Copyright &y& Elsevier]

Highlights: [•] The fluorescence properties of 2.7μm emission and energy transfer mechanism are investigated. [•] The optimized concentration ratio of Er3+ to Ho3+ is found to be 1:1. [•] The sample possesses large emission cross section and radiative transition probability. [•] The energy transfer microparameters are calculated and discussed. [ABSTRACT FROM AUTHOR]

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]

The paper studies the influence of co-doping with alkali metal ions (Na+, Mg2+) on fast interconfigurational 5 d-4f luminescence in LiSrPO 4 doped with Pr3+. Na+ and Mg2+ ions were introduced in order to provide charge compensation and modify the electronic configuration of the materials. Luminescent properties of the powder samples were investigated using time-resolved pulsed cathodoluminescence and luminescence spectroscopy in the UV-VUV spectral region. The obtained results were compared with those obtained earlier on LiSrPO 4 :Pr3+ without co-dopants. With introduction of the co-dopants, slight changes in relative luminescence intensity and decay time of Pr3+ ion 4f 1 5d 1 -4f 2 radiative transitions were found. The study revealed a complex interplay between defects of crystalline structure and impurity ions leading to the peculiarities in energy relaxation processes. Energy transfer leading to the delayed recombination processes is responsible for significant afterglow in Pr3+ 4f 1 5d 1 -4f 2 emission. [Display omitted] • LiSrPO 4 :Pr3+,Na+/Mg2+ crystalline powders were synthesized via solid state reaction. • Emission and decay kinetics were studied upon UV-VUV and cathode ray excitation. • 5 d-4f Pr3+ emission shows fast decay (τ < 20 ns) with secondary slower components. • Defects of unknown nature negatively influence the relaxation processes. • Na+ and Mg2+ as co-dopants almost insignificantly improve luminescence properties. [ABSTRACT FROM AUTHOR]

• Eu 2 O 3 doped glasses have been synthesized in Magnesium based glasses. • Energy transfer characteristics has been observed in these glasses. • Judd-Ofelt analysis have been evaluated and compared. • A strong red-orange emission at 5D o →7F 2 transition around 613 nm is observed. • The prepared glasses have shown potential results to be used as optical device applications. This work focuses on the luminescence properties of Eu 2 O 3 -doped borate glasses developed by the high-temperature-melting method. The appropriate spectroscopic methods have been used to selectively analyze absorption, excitation, energy transfer, and photo-stimulated luminescence (PSL). The parameters, viz. oscillator strengths, stimulated emission cross-sections, radiative transition probability, and branching ratios, essential for luminescence, are extracted both without and with thermal correction applying to 7F 0 → 5D 2 and 7F 6 by using the theoretical Judd Ofelt (JO) model. By employing the IH model to the decay kinetics, the dipole-dipole interaction mechanism is evaluated. The color chromaticity confirms the red-orange luminescence of the prepared glasses. We observe significant changes in the Gd3+: 6P 7/2 –8S 7/2 and Eu3+:5D o –7F 2 luminescence which is attributed to the energy transfer from the 6P 7/2 state of the Gd3+ to 5D o of the Eu3+. These results recommend these glasses for lasers and other optical device applications. [ABSTRACT FROM AUTHOR]

Bulk and nanosized GdVO:Dy phosphors were prepared via a simple co-precipitation process, and their crystal structure, morphology, and spectral properties were studied. It is found that electric dipole-dipole interaction was hindered in the nanosized samples based on the analysis of the dependence of luminescent intensity on the Dy doping concentration. The decay time of the F level in the nanosized GdVO:2 mol% Dy sample is determined to be longer than that in the 0.3 mol% Dy doped bulk sample. Moreover, the fluorescent lifetime of this level in the nanosized sample is strongly dependent on the index of refraction of the medium surrounding the nanoparticles, and a 0.68 filling factor was obtained. The intrinsic radiative lifetimes and internal quantum efficiencies of the F level of Dy in the nanosized and bulk samples were obtained, which indicate that the internal quantum efficiency of nanosized sample is higher than that of the bulk sample, but the external quantum efficiency is lower. [ABSTRACT FROM AUTHOR]

Abstract: Spectroscopic properties of Sm3+-doped phosphate and fluorophosphate glasses of the composition (60−x/2) P2O5 +15 K2O+(15−x/2) SrO+10 Al2O3 +x Sm2O3 (PKSASm) and (54−x/2) P2O5 +14 K2O+10 KF+(13−x/2) SrO+9 Al2O3 +x Sm2O3 (PKFSASm), where x=0.1, 0.5, 1.0, 2.0, 4.0 and 6.0mol%, have been investigated. The oscillator strengths and the intensity parameters (Ω2, Ω4 and Ω6) have been determined using the Judd–Oflet theory, which in turn is used to predict the radiative transition probability (AR), radiative lifetime (τR) and branching ratios for the fluorescent 4G5/2 level. The higher stimulated emission cross-sections, 12.27×10−22 and 14.12×10−22 cm2 have been observed for the 4G5/2 → 6H9/2 transition of PKSASm10 and PKFSASm10, respectively. The non-exponential nature of the decay curves of the 4G5/2 level increases with increase in Sm3+ ion concentration accompanied by decrease in lifetime. The non-exponential decay curves have been best fitted to the generalized Yokota–Tanimoto model indicating that the energy transfer among optically active ions is through dipole–dipole interaction. [Copyright &y& Elsevier]

Abstract: Two covalently linked boron dipyrromethene (BODIPY) dyads containing meso-phenyl BODIPY and meso-furyl BODIPY units connected via meso-meso and meso-α positions were synthesized by a Pd(0) coupling reaction. The dyads are freely soluble in common organic solvents and their structures were confirmed by HR-MS, 1D and 2D NMR techniques. Absorption studies indicate that the meso-aryl BODIPY and the meso-furyl BODIPY absorb in two different regions and that the meso-furyl BODIPY absorbs at lower energy compared to the meso-aryl BODIPY. The steady state fluorescence studies carried out by exciting the meso-aryl BODIPY unit clearly indicated an efficient singlet–singlet energy transfer from the meso-aryl BODIPY unit to meso-furyl BODIPY unit in both dyads. Furthermore the meso-α linked BODIPY dyad (ϕ f =0.41) is more fluorescent than its corresponding BODIPY monomers whereas the meso-meso linked BODIPY dyad (ϕ f =0.017) is weakly fluorescent. This unexpected observation was tentatively attributed to the restricted rotation of the BODIPY units in the meso-α linked dyad resulting in enhancement of radiative transitions. The time-resolved fluorescence study also indicated that meso-α linked BODIPY dyad is more fluorescent with singlet state lifetime of 3.7ns. The DFT studies carried out on dyads are in agreement with the experimental observations. [Copyright &y& Elsevier]

The article focuses on the study for the optical properties of colloidal photonic crystals (CPhCs). It discusses the fabrication techniques for CPhCs as well as their structures, photonic band gap, and fluorescence. It highlights the influence of photonic band gap, matching the energy of radiative transition, on the suppression of emission, which is used in resonance energy transfer; thus, improves photonic crystal (PhC)'s optical confinement.

Abstract: This paper presents the optical characterization of Nd3+ ions in nanostructured SiO2–Na2CO3–Al2O3–B2O3 (SNAB) CdS glass, synthesized by fusion. Radiative properties of the glass were determined by absorption, luminescence spectroscopy and lifetime measurements. Nd3+ emission enhancement and quenching were investigated in the presence of CdS nanocrystals. Nd3+-emission quenching was attributed to upconversion mechanisms and nonradiative processes such as multiphonon decay and energy transfer, while the Nd3+-emission enhancement was due to energy transfer from the CdS nanocrystals. Changes in the chemical environment around CdS nanocrystals were also confirmed by Judd–Ofelt calculations. [Copyright &y& Elsevier]

The Prdoped PbO-GeO glass samples have been synthesized by melting and quenching process. The nephelauxetic ratio, covalency and bonding parameter which provides the information about the type of bonding between the rare earth ion and neighbor oxygen atoms calculated. The optical parameters such as radiative transition probabilities, radiative lifetime, branching ratios etc. of Pr ions have been determined by Judd-Ofelt analysis. An upconversion emission using the excitation at ~594 nm supported by energy transfer process due to dipole-dipole interaction in the D metastable state has been found. [ABSTRACT FROM AUTHOR]

Abstract: Tm3+-doped and Tm3+/Yb3+-codoped TeO2–ZnO–Bi2O3 (TZB) glasses are prepared by melt-quenching method. The Judd-Ofelt intensity parameters (Ω t t =2, 4, 6), radiative transition rate, and radiative lifetime of Tm3+ are calculated based on the absorption spectra. The 1.8μm emission of the samples is investigated under 980nm laser excitation. The absorption, emission cross-sections, and gain coefficient of Tm3+:3F4 → 3H6 are calculated. The energy transfer processes of Yb3+–Yb3+ and Yb3+–Tm3+ are analyzed, the results show that the Yb3+ ions can transfer their energy to Tm3+ ions with large energy transfer coefficient, and a maximum efficiency of 79%. [Copyright &y& Elsevier]

Abstract: TmF3 doped TeO2–ZnO–La2O3 (TZL) glasses and fibers have been prepared by the conventional melt-quenching and suction casting methods, respectively. 2μm emission properties and energy transfer mechanisms of the TZL glasses and fibers have been analyzed and discussed. The oscillator strength, Judd–Ofelt parameters, radiative transition probability and radiative lifetime of Tm3+ have been calculated based on the absorption spectra and Judd–Ofelt theory. The maximum emission cross-section of Tm3+ is 6.9×10−21 cm2 near 2μm. Emission spectra have been obtained from both TZL fibers and bulk glass when excited with a 794nm pump. The results of 2μm emission spectra indicate that the line width of Tm3+ measured in fibers is narrower than that in the bulk glass sample. The peak position of the emission spectra shifts to longer wavelength with increment of the fiber length. [Copyright &y& Elsevier]

Abstract: The spectroscopic properties of tellurite glasses of composition (in mol%) TNKNd: (70− x)TeO2–15Nb2O5–15K2O–xNd2O3 (x =0.1, 1.0, 1.5, 2.0 and 2.5) and TNLNd10: 69TeO2–15Nb2O5–15Li2O–1.0Nd2O3 and lithium metaborate glass of composition LBNNd10: 89LiBO2–10Nb2O5–1.0Nd2O3 have been investigated using absorption and emission spectra and decay curve analysis. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands, using the free-ion Hamiltonian model. The spectral intensities have been calculated by using the Judd–Ofelt theory and in turn the radiative properties such as radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes have been estimated. The decay curves at the lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (⩾1.0mol%) due to energy transfer processes. The effective lifetimes for the 4F3/2 level are found to decrease with increase in Nd2O3 concentration for all the glasses under investigation. The non-exponential decay curves have been well-fitted to the Yokota–Tanimoto model with S =6, indicating that the nature of energy transfer is of dipole–dipole type and energy migration also plays an important role. The results obtained have been compared with Nd3+-doped phosphate, fluorophosphate, lead borate, tellurite, germanate and silicate glasses and Nd3+-doped YAG ceramic and Ca2Nb2O7 crystals. [Copyright &y& Elsevier]

Abstract: Ho3+/Yb3+ codoped lanthanum–tungsten–tellurite (TWL) glasses are prepared by melt-quenching method. The Judd–Ofelt intensity parameters (Ωt t =2, 4, 6), radiative transition rates, radiative lifetimes, and branching ratios of Ho3+ are calculated based on the absorption spectrum to evaluate the spectroscopic properties of Ho3+ in TWL glass. The mid-infrared emission of the samples are investigated under the excitation of 980nm LD. The absorption, emission cross-sections and gain coefficient of Ho3+:5I7 → 5I8 are calculated. The energy transfer processes of Yb3+–Yb3+ and Yb3+–Ho3+ are analyzed, the results show that the Yb3+ ions can transfer their energy to Ho3+ ions with large energy transfer coefficient, and a maximum efficiency of 84%. [ABSTRACT FROM AUTHOR]

Abstract: Fluorophosphates glasses YF3–BaF2–Ba(PO3)2 doped with Er3+ and Er3+–Yb3+ were prepared and the structures of the samples were briefly investigated. The experimental intensity parameters were calculated according to the Judd–Ofelt theory, from which the radiative transition probabilities, fluorescence branching ratios, and radiative lifetimes of Er3+ were obtained. Bright green and red upconversion emissions was observed in Er3+–Yb3+ co-doped samples excited by 980nm laser diode, and two-photons absorption processes were determined for the emissions by examining the dependence of the emission intensity on the excitation power. The concentration effects on the intensity and decay time of the upconversion emission revealed that growing Er3+ concentration declined the probability of sequential energy transfer from Yb3+ to Er3+, and thus increasing the intensity ratio of the red emission to the green ones. The temperature effects on the intensity ratios of different emission bands showed that the maximum transducer sensitivity based on the fluorescence intensity ratio (FIR) was calculated to be 0.0015/°C at 6°C. [Copyright &y& Elsevier]

Abstract: By using Yb3+ and Er3+ as double sensitizers and 980nm laser as pump light, unusual radiative transitions 5H3–7 → 7F0–3, 5L6 → 7F0, 5D3 → 7F2,3, and 5D2 → 7F0,1,2,3 of Eu3+ ions in NaYF4 nanocrystals were observed. 5H3–7, 5L6, and 5D2,3 levels of Eu3+ have been populated by two-step energy transfer process of Yb3+ →Er3+ →Eu3+ and become efficient radiative levels in the upconversion scheme. Experimental data indicate that when the excited Er3+ ions serve as donors, it is easier to transfer energy to acceptors after they are excited to the levels with longer lifetime. [Copyright &y& Elsevier]

A new series of optically translucent borosilicate glasses activated with varying concentrations of Dy3+ ions were fabricated by employing melt quenching method. Spectral investigations were conducted by recording the absorption, photoluminescent (PL) excitation and PL emission for Dy3+ activated borosilicate glasses. The absorption spectral information was exposed to Judd-Ofelt (J-O) analysis to calculate various radiative properties such as transition probability, total transition probability, branching ratios and radiative lifetimes of the as synthesized glasses. The excitation spectrum recorded under 483 nm emission wavelength possess a sharp peak at 348 nm in 0.1 mol% of Dy3+ ions doped borosilicate glass. Emission spectra recorded for all the Dy3+ ions activated borosilicate glasses under 348 nm intense excitation wavelength exhibit two potential peaks in visible region at 483 nm (4F 9/2 → 6H 15/2) and 575 nm (4F 9/2 → 6H 13/2). The emission centered at 483 nm is most prominent. Radiative properties measured from the absorption spectral feature were correlated with emission spectral information to estimate emission cross-section, gain bandwidth and optical gain parameters to understand the utility of the as synthesized glasses as photonic devices. The CIE coordinates measured for all the titled glasses are in good proximity with the white light coordinates of CIE 1931 diagram. • LPZABS glasses with Dy3+ ions were prepared by using melt quench technique. • XRD recorded for all the as prepared glasses confirm the glassy nature. • The bonding nature between Dy3+ ions and the surrounding ligands is ionic in nature. • Energy transfer through dipole-dipole interaction leads to concentration quenching. • CIE of 1.5mol% of Dy in LPZABS glasses are in proximity with CIE of white light. [ABSTRACT FROM AUTHOR]