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The CsCaI 3 single crystals doped with Tm 2+ were grown by Bridgman technique. Divalent thulium luminescence related to the 4f 13 -4f 13 intra-configurational and 4f 12 5d 1 -4f 13 inter-configurational transitions were analyzed as a function of temperature. Excited state excitation spectroscopy has been applied within a wide spectral range to examine peculiarities of transitions between different 4f 12 5d 1 excited states of Tm 2+ . This two-color excitation experiment was useful to assess d-d photon-absorption processes that are relevant to observed up-conversion phenomena attributed to effective anti-Stokes green luminescence around 550 nm. Furthermore, activation energy of 4f 12 5d 1 → 4f 13 luminescence quenching was estimated and high value of 2 F 5/2 → 2 F 7/2 emission cross-section was determined in CsCaI 3 :Tm 2+ . Our spectroscopic study was performed to complement and verify the previous investigation in this field. [ABSTRACT FROM AUTHOR]

Optical absorption and emission spectra of Dy 3+ ions in Gd 3 Ga 3 Al 2 O 12 single crystal were investigated at room temperature and T = 5 K in the visible (VIS) and near-infrared (NIR) region. Low-temperature spectra were utilized to determine the energy level structure of Dy 3+ in the GGAG host. The detailed analysis implied that optically active ions reside mainly into well-defined sites in the crystal studied. Judd–Ofelt (JO) theory was used to calculate oscillator strengths, transitions intensity parameters Ω 2,4,6 , radiative transition probabilities, luminescence branching ratios and radiative lifetime of dysprosium luminescent level. Relaxation dynamic of 4 F 9/2 excited state was examined as a function of temperature. High quantum efficiency of dysprosium luminescence level, value of the 4 F 9/2 → 6 H 13/2 yellow emission cross-section and the quality of remaining spectroscopic parameters indicate that the Gd 3 Ga 3 Al 2 O 12 :Dy 3+ optical system can be considered as promising phosphor and visible laser material. [ABSTRACT FROM AUTHOR]

Single crystal of LaGaTaO (LGT) containing intentionally 0.5 % of Ho and 1 % of Yb was grown by the Czochralski method. Examination of chemical composition of the grown crystal revealed that luminescent holmium and ytterbium ions are preferably retained in the melt and their actual concentrations are 0.12 and 0.24 %, respectively. Spectroscopic investigation performed encompassed IR host absorption spectra and Raman spectra at room temperature, optical absorption and luminescence spectra of Ho and Yb at room temperature and at 5 K, and luminescence decay curves at room temperature. It was found that all spectral bands recorded show important inhomogeneous line broadening. This feature was attributed to structural disorder inherent to the crystal lattice in which pentavalent Ta ions occupy octahedral Ga(1) sites together with trivalent Ga ions. Despite small concentrations of luminescent ions, the occurrence of nonradiative interaction that feeds the I and I levels of Ho ions by transfer of an excitation from the F level of Yb ions was evidenced. Based on examination of spectroscopic parameters evaluated, it was concluded that LGT:Ho, Yb may be considered as a potential intermediate-gain laser active material able to emit infrared radiation from the I → I transition of Ho around 2 micrometres upon laser-diode pumping into Yb absorption band. [ABSTRACT FROM AUTHOR]

For the first time ever, the luminescence spectra of Cr centers in two chlorite crystals are presented. Chromium ions occupy the strong crystal-field site M4 in the brucite sheet and the intermediate crystal-field site in the inner octahedral sheet for purple and green chlorite, respectively. We discuss the influence of an effective positive charge on the Cr ion and an effective negative charge of ligands on the differences in the values of the Dq and B parameters. It is concluded that the presence of Fe ions and other point defects, as well as concentration quenching, causes the very short luminescence lifetimes of chromium ions. [ABSTRACT FROM AUTHOR]

Optical absorption, luminescence excitation, and emission spectra as well as luminescence kinetics of the Sm- and Yb-doped glasses with lithium tetraborate (Li2B4O7) composition were investigated and analysed. The Sm- and Yb-doped lithium tetraborate glasses of high optical quality were obtained in air from corresponding polycrystalline compounds according to standard glass synthesis technology. The Sm and Yb impurities were added to the Li2B4O7 compound in the form of Sm2O3 and Yb2O3 oxides in amount of 0.4 mol%. Using optical and electron paramagnetic resonance spectroscopy it was shown that the Sm and Yb impurities are incorporated into the lithium tetraborate glass network as Sm3+ (4f5, 6H5/2) and Yb3+ (4f13, 2F7/2) ions, exclusively. All of the observed transitions in the absorption and luminescence spectra of Sm3+ and Yb3+ centres were identified. The luminescence kinetics of the Sm3+ and Yb3+ centres in the Li2B4O7 glass are characterised by a single exponential decay. Decay constants for the main emission transitions of the Sm3+ and Yb3+ centres in the lithium tetraborate glass were obtained at T = 300 K. Incorporation peculiarities and optical spectra of Sm3+ and Yb3+ ions in the lithium tetraborate glass have been discussed in comparison with other borate glasses and crystals. [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]

Single crystal of La 3 Ga 5.5 Ta 0.5 O 14 (LGT) doped with Dy3+ was fabricated by the Czochralski technique and investigated employing methods of optical spectroscopy. Polarized optical absorption spectra and luminescence spectra were recorded at room temperature. Unpolarized absorption and luminescence spectra were recorded at 10 K. Spectra of blue luminescence related to transitions 4I 15/2 , 4F 9/2 → 6H 15/2 were recorded at several temperatures in the 300–773 K region. Dy3+ ions have the same symmetry sites in LGT but their spectra show inhomogeneous broadening due to structural disorder of the host and are markedly anisotropic. Results of the Judd-Ofelt treatment made it possible to assess emission cross sections for the 4F 9/2 → 6H 15/2 blue luminescence and for the 4F 9/2 → 6H 13/2 yellow luminescence employing Fuchtbauer-Ladenburg formula and reciprocity method. In particular, a spectral distribution of La 3 Ga 5.5 Ta 0.5 O 14 : Dy3+ σ-polarized luminescence band with an emission cross section σ em = 0.51 × 10−20 cm2 at 573.5 nm is favorable for a laser operation in the visible. Interpretation of the effect of temperature on the blue emission spectra leads to the conclusion that La 3 Ga 5.5 Ta 0.5 O 14 : Dy3+ is promising for application as luminescent thermometer. • Novel single crystal La 3 Ga 5.5 Ta 0.5 O 14 :Dy (LGT:Dy). • Detailed analysis of optical spectra and luminescence decay curves. • Potential visible laser operation at 573.5 nm. • Temperature sensitivity of LGT:Dy luminescence. [ABSTRACT FROM AUTHOR]

The Y 2-x Te 4 O 11 (x = 0.1, 0.5, 1.0, 2.0 and 5.0 at%) microcrystalline powders were successfully synthesized by a conventional solid state reaction method. Optical absorption (300 K) and fluorescence spectra (300 K) as well as fluorescence decay curves (300 K) of the emitting levels of Tm 3+ ion in Y 2 Te 4 O 11 powders are presented and analyzed in details. The Judd-Ofelt theory was applied to analyze experimental data for the quantitative determination of phenomenological Ω λ ( λ  = 2, 4, 6) parameters, radiative transition probabilities ( A ), branching ratios ( β ) of luminescence and radiative lifetimes ( τ rad ) of the 1 D 2 , 1 G 4 , 3 H 4 and 3 F 4 levels. The observed non-exponential decays nature and concentration quenching of the 1 G 4 and 3 H 4 states have been attributed to cross-relaxation processes and this phenomena has been analyzed by Inokuti-Hirayama model. The stimulated emission cross-section for the 3 F 4 → 3 H 6 transition equals to 1.12 × 10 −20 cm 2 at 1809 nm was calculated using the Füchtbauer-Ladenburg method and compared with the corresponding values of other Tm 3+ -doped laser hosts. From obtained results, follow that the Tm 3+ :Y 2 Te 4 O 11 is a potential candidate for a solid-state laser host operating at 1.8 µm. [ABSTRACT FROM AUTHOR]

Spectroscopic and luminescent properties of the Pr-doped and Pr–Ag co-doped borate glasses with Li 2 B 4 O 7 (Li 2 O–2B 2 O 3) composition are studied and discussed. Experimental and theoretical oscillator strengths (f exp and f theor), phenomenological parameters (Ω 2 , Ω 4 , Ω 6), radiative properties (A rad , β , τ rad), and quantum efficiencies (η) of the Pr3+ luminescence were calculated basing on the obtained experimental results and Judd–Ofelt theory. Most intense band of the Pr3+ luminescence is peaked at 601 nm (1D 2 → 3H 4 transition). Presence of the isolated Ag+ (4 d 10, 1S 0) ions, small non-plasmonic Ag aggregates (Ag m n + nanoclusters), and plasmonic Ag metallic nanoparticles in the Li 2 B 4 O 7 :Pr,Ag glass was proposed basing on analysis of the photoluminescence and optical absorption spectra. Observed enhancement of luminescence intensity and increasing of stimulated emission cross-section and quantum efficiency of luminescence in the Li 2 B 4 O 7 :Pr,Ag glass is explained by energy transfer from Ag species to the Pr3+ ions as wells local-field effect induced by Ag nanoparticles. • The Pr-doped and Pr–Ag co-doped Li 2 B 4 O 7 glasses of high optical quality were obtained. • Optical absorption, EPR, photoluminescence spectra and decay kinetics were studied. • Judd-Ofelt parameters (Ω 2 , Ω 4 , Ω 6) and radiative properties (A rad , β , τ rad , σ em , η) were calculated. • Enhancement of the Pr3+ emission intensity in the Li 2 B 4 O 7 :Pr,Ag glass was observed. • Mechanisms of the Pr3+ luminescence improvement in the Li 2 B 4 O 7 :Pr,Ag glass is proposed. [ABSTRACT FROM AUTHOR]

Spectroscopic and luminescent properties of the Nd-doped and Nd–Ag co-doped borate glasses with Li 2 B 4 O 7 (Li 2 O–2B 2 O 3) basic composition are investigated and analysed using optical absorption, electron paramagnetic resonance (EPR), photoluminescence (excitation, emission, decay kinetics) experimental methods and Judd–Ofelt analysis. Optical absorption, photoluminescence spectra and decay kinetics of Nd3+ ions were registered and detailed analysed. Experimental and theoretical oscillator strengths (f exp and f theor), Judd–Ofelt intensity parameters (Ω 2 , Ω 4 , Ω 6), and important to laser applications radiative parameters such as probabilities of radiative transitions (A rad), branching ratios of luminescence (β), radiative lifetimes (τ rad), emission cross-sections (σ em), and quantum efficiency (η) of the Nd3+ luminescence in the Li 2 B 4 O 7 :Nd and Li 2 B 4 O 7 :Nd,Ag glasses have been calculated. Broad absorption band of surface plasmon resonance (SPR) related to silver nanoparticles was observed in the Li 2 B 4 O 7 :Nd,Ag glass. Presence of the Ag paramagnetic centres and aggregates in the Li 2 B 4 O 7 :Nd,Ag glass was confirmed by EPR spectroscopy. Photoluminescence emission and excitation spectra as well as decay kinetics of the Ag+ ions and small non-plasmonic Ag aggregates or nanoclusters were registered and discussed. Observed enhancement of the Nd3+ luminescence intensity in the Li 2 B 4 O 7 :Nd,Ag glass is explained by effects induced by SPR of the Ag nanoparticles as wells energy transfer from Ag+ ions and Ag aggregates to the Nd3+ ions. Image 1 • The Nd-doped and Nd–Ag co-doped Li 2 B 4 O 7 glasses of high optical quality were obtained. • Optical absorption, EPR, photoluminescence spectra and decay kinetics were studied. • Judd-Ofelt parameters (Ω 2 , Ω 4 , Ω 6) and radiative properties (A rad , β , τ rad , σ em , η) were calculated. • Enhancement of the Nd3+ luminescence in the Li 2 B 4 O 7 :Nd, Ag glass was obtained. • Silver co-doping improves luminescent and laser properties of the Nd3+-doped borate glasses. [ABSTRACT FROM AUTHOR]

[Display omitted] • A series of Pb-containing glasses of high optical quality and chemical purity are obtained. • XRD, IR transmission, UV-Vis absorption & photoluminescence of obtained glasses are studied. • Intrinsic photoluminescence broad bands in the visible range were discovered and analysed. • Fast and slow recombination mechanisms for intrinsic photoluminescence bands were proposed. • The studied glasses are perspective luminescent materials of the visible spectral range. The X-ray diffraction, infrared transmission, optical absorption, photoluminescence spectra and decay kinetics of a series of un-doped Pb-containing glasses with compositions of 0.4PbO–0.6GeO 2 , 0.6PbO–0.4SiO 2 , 0.7PbO–0.3B 2 O 3 , and 0.54PbO–0.34B 2 O 3 –0.12GeO 2 were studied. Average interatomic distances and coordination numbers for main structural units GeO 4 , SiO 4 , BO 4 , BO 3 , and PbO n (n = 3 – 6) in all studied glasses were derived from radial distribution functions. The 0.4PbO–0.6GeO 2 and 0.54PbO–0.34B 2 O 3 –0.12GeO 2 glasses upon UV photoexcitation show intense broad emission bands with maxima at 478 and 543 nm, respectively, and weaker broad band with peak about 610 nm. Based on luminescence decay kinetics analysis were proposed fast (band-to-band recombination) and slow (recombination with participation of point defects) mechanisms of intrinsic luminescence in the 0.4PbO–0.6GeO 2 and 0.54PbO–0.34B 2 O 3 –0.12GeO 2 glasses. The 0.6PbO–0.4SiO 2 and 0.7PbO–0.3B 2 O 3 glasses under UV – violet photoexcitation reveal only broad emission band with a maximum at 599 and 593 nm, respectively, caused by the band-to-band fast recombination mechanism. [ABSTRACT FROM AUTHOR]