Composition dependent structural and optical properties of Sm-doped sodium borate and sodium fluoroborate glasses

Sodium borate and fluoroborate glasses doped with trivalent samarium (Sm³⁺) were prepared and their detailed spectroscopic analysis was carried out. The FTIR spectra reveal that, the glasses contain BO₃, BO₄, non-bridging oxygen and strong OH⁻ bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross section () and branching ratios (β_R) for the excited levels of Sm³⁺ ions in sodium borate and sodium fluoroborate glasses. The dependence of the spectral characteristics of Sm³⁺ ions due to compositional changes have been examined and reported. The value is found to decrease with the decrease in the sodium content in the glass. The decay from the ⁴G_5/2 level is found to be non-exponential indicating a cross-relaxation among the Sm³⁺ ions.     

Composition dependent structural and optical properties of Sm doped boro-tellurite glasses

Boro-tellurite glasses with the composition (69-x)H₃BO₃+xTeO₂+15MgCO₃+15K₂CO₃+1Sm₂O₃ (where x=0, 10, 20, 30 and 40 wt%) doped with trivalent samarium have been prepared and their structural and spectroscopic behavior were studied and reported. The FTIR spectra reveal the presence of BO₃ and BO₄ non-bridging oxygen as well as strong OH⁻ bonds in the prepared glasses. Through the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and the same is in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross-section () and branching ratios (β_R) for the excited levels of Sm³⁺ ions corresponding to ⁴G_5/2→⁶H_5/2, ⁴G_5/2→⁶H_7/2, ⁴G_5/2→⁶H_9/2 and ⁴G_5/2→⁶H_11/2 transitions. Structural and spectral dependence of the Sm³⁺ ions due to the compositional changes have been examined and reported. The lifetime of the ⁴G_5/2 level is found to be non-exponential for all the prepared glasses indicating a cross-relaxation among the Sm³⁺ ions. The structural and spectroscopic results corresponding to compositional changes have been compared with the similar studies and reported.     

Absorption and emission spectral studies of Sm and Dy doped alkali fluoroborate glasses

Absorption and photoluminescence spectra of Sm³⁺ and Dy³⁺ doped alkali fluoroborate glasses of the composition 90.5% B₂O₃+4% AlF₃+5% MF+0.5% LnF₃ (M=Li, Na, K and Ln=Sm, Dy) have been reported. On excitation, with , the Sm³⁺ glasses are found to be orange fluorescent in color and richness of that color is high in the Na+ glass, compared to Li⁺ and K⁺ glasses. Similarly, on excitation with , the Dy³⁺ glasses are fluorescent yellow in color and that color is richer in the K⁺ glass.     

Characterization of Tm doped mixed alkali borate glasses—spectroscopic investigations

The effect of mixed alkalis on the optical absorption spectra of Tm³⁺ in xNa₂O·(30−x)K₂O·70B₂O₃ glasses has been studied. The optical band gap values (E_opt) for both direct and indirect transitions have been obtained using Davis and Mott theory. Spectroscopic parameters like Racah (E¹, E² and E³), spin-orbit (ξ_4f) and Judd-Ofelt intensity parameters (, and ) have been calculated for different x values. Radiative transition probabilities (A_rad), radiative lifetimes (τ_R), branching ratios (β), integrated absorption cross sections (Σ) and multiphonon relaxation rates (W_MPR) are calculated for certain excited states of Tm³⁺ ion. The observed trends in the above parameters as a function of x in these borate glasses have been discussed keeping in view the effect of mixed alkalies in borate glasses. Certain potential lasing transitions have been identified for laser action among the various transitions of Tm³⁺ in these mixed alkali borate glasses.     

Dysprosium doped alkali fluoroborate glasses—Thermal, structural and optical investigations

Thermal, structural and optical properties of Dy³⁺-doped alkali fluoroborate glasses with composition (in mol%), 49B₂O₃+25XO+25NaF+1Dy₂O₃ (where X=Li₂, Na₂, K₂, Mg and Ca), have been investigated. Thermal analysis revealed the homogeneous formation of the glasses. The FTIR spectra reveal that the glasses contain BO₃, BO₄ non-bridging oxygen atoms and strong OH⁻ bonds. From the optical absorption spectra, Judd-Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probability (A), stimulated emission cross-section () and branching ratios (β_R) for the excited levels of Dy³⁺ ions in alkali fluoroborate glasses. The dependence of the spectral characteristics of Dy³⁺ ions due to compositional changes has been examined and reported.     

The luminescence of Sm in alkaline earth borophosphates

The temperature-dependent luminescence of Sm²⁺ ions in MBPO₅ was studied. At low temperature, Sm²⁺ in this series shows 4f⁶→4f⁶ luminescence with only a single emission line observed for the transition, revealing that only one crystallographic cationic site is available for Sm²⁺ in all the hosts. With increasing temperature, the emission intensity of the transition increases whereas that of the transitions decreases. The transitions of Sm²⁺ were observed in BaBPO₅ and its intensity increases with increasing temperature. At , a broad band of the 4f⁵5d→4f⁶ luminescent transition of Sm²⁺ in SrBPO₅ and BaBPO₅ with maximum at appears due to the thermal population. The lifetime of the transition was recorded at different temperatures, showing a single exponential decay for Sm²⁺ in SrBPO₅ and BaBPO₅ but a non-single-exponential decay in CaBPO₅.     

Optical properties of Sm-doped CaF2 bismuth borate glasses

Sm³⁺-doped calcium fluoride bismuth borate glasses were prepared and characterized optically and the oscillator strengths and Judd–Ofelt parameters for the glass containing 1.5 mol% of Sm₂O₃ were calculated. Density and optical absorption, transmission and the emission spectra were measured. The values of Judd–Ofelt parameters suggested an increase in the degree of asymmetry the local ligand field at Sm³⁺ sites. The optical band gap energy, band tailing parameter and Urbach's energy were calculated for all glass samples. It was found that with increasing the concentration of Sm₂O₃ content the values of the optical band gap energy decrease whereas Urbach's energy increases. Absorption and excitation spectra indicate that commercial UV and blue laser diodes, blue and bluish-green LEDs and Ar⁺ optical laser are powerful excitation sources for Sm³⁺ visible fluorescence in the glass.     

Optical transitions and frequency upconversions of Ho and Ho/Yb ions in Al(NO3)3-SiO2 sol-gel glasses

Infrared-to-visible upconversion processes and Judd Ofelt intensity parameters were analyzed for Ho³⁺ singly doped and Ho³⁺/Yb³⁺ co-doped Al(NO₃)₃-SiO₂ glasses with a fixed Ho³⁺ and Yb³⁺ concentrations prepared by sol-gel method. Blue and intense green upconversion emissions centered at 467 and 538 nm, corresponding to the and transitions, respectively, were observed under 800 nm excitation. The analysis of the dynamics of upconversion emissions suggest excited state absorption, energy transfer and back transfer as the possible causes for the observed transitions. Significant enhancement of upconversion intensities in Ho³⁺/Yb³⁺ co-doped glass compared to the Ho³⁺ singly doped one confirms efficient energy transfer between Yb³⁺ and Ho³⁺ ions. Intense upconversion emissions shown by the glasses in the present study indicate their potential in upconversion device applications.     

Physicochemical, structural and fluorescence properties of Er-doped Ge-S-Ga glasses

Erbium-doped (GeS₂)_x(Ga₂S₃)_100−x (x=75, 80, 85, 90 mol%) glasses have been characterized by some basic parameters, which are important from a practical point of view. The influence of Er by introduction of 0.3, 0.6, and 0.9 mol% Er₂S₃ on the properties has been studied. The glasses have relatively high glass transition temperatures and high thermal stability, the maximal being at x=80 (the difference between the crystallization and glass transition temperatures has been found to be 150 °C. The values of Vickers microhardness and density increase with increasing GeS₂ content, slightly depending on the presence of the Er³⁺ ions. The distribution and changes of the structural units, caused by addition of Ga₂S₃ and Er₂S₃ to GeS₂, have been specified by the Raman scattering in the range 50-550 cm⁻¹. The intensity dependence of the luminescence on glass composition has been evaluated. The glasses have shown a good chemical durability and their resistance to the moisture is relatively high. The obtained results have supported possible applications of these glasses in rare-earth doped devices.     

Judd-Ofelt parameters of Er in transparent TeO2-based nanocrystallized glasses

Transparent Er³⁺-doped bulk nanocrystallized (size of nanocrystals: ∼40 nm) glasses of 15K₂O·15Nb₂O₅·70TeO₂·0.5Er₂O₃ and 10BaO·10Gd₂O₃·80TeO₂·0.5Er₂O₃ are prepared, and the Judd-Ofelt parameters, (t=2, 4, 6), of Er³⁺ are evaluated from optical absorption spectra. The change in the molar polarizability due to the nanocrystallization is small in both samples, but a clear decrease in the mean atomic volume due to the nanocrystallization, i.e. more close atom packing, is observed. In both systems, a large decrease is observed in the parameter due to the nanocrystallization, indicating that the degree of the site symmetry of Er³⁺ ions in nanocrystallized glasses is much higher than that in the precursor glasses. The decrease in the and parameters due to the crystallization is small, suggesting that the covalency of Er³⁺-O bonds in nanocrystals is not so different from that in the precursor glasses.     

Optical characterization of Cu ion-doped zinc lead borate glasses

We have developed a new series of zinc lead borate (ZLB) glasses by varying ZnO content, to enhance UV transmission, in the chemical composition of xZnO-15PbO-(85−x)B₂O₃, where x=0, 5, 10, 15, 20, 25, 30, 35, 40 and 45 mol% ZnO. From the measurement of UV absorption spectra both the direct and indirect band gaps have been evaluated. Also different physical properties of a reference glass of 45ZnO-15PbO-40B₂O₃ have been studied. From the measurement of refractive indices at six different wavelengths, Cauchy's constants (A=1.578743209; and ) have been computed and a satisfactory correlation has been achieved between the theoretical and the experimental results. Absorption spectra of Cu²⁺(45−x)ZnO-15PbO-40B₂O₃ (where x=0.1, 0.2, 0.5 and 1.0 mol%) have shown two absorption bands at 428 nm (²B_1g→²E_g) and 777 nm (²B_1g→²B_2g). Emission spectra of (1.0 mol%) Cu²⁺:ZLB have revealed two emission transitions at 400 and 493 nm with excitations at 288 and 316 nm.     

Novel phosphors of Eu, Tb or Bi activated Gd2GeO5

Novel phosphors of or Bi³⁺ doped Gd₂GeO₅ were synthesized and their photoluminescent and cathodoluminescent properties were investigated. (Gd_1−xEu_x)₂GeO₅ and (Gd_1−xTb_x)₂GeO₅ formed continuous solid solution in the range of x=0.0-1.0. Gd₂GeO₅:Eu³⁺ and Gd₂GeO₅:Bi³⁺ presented bright red and blue luminescence for both UV and cathode ray excitation, respectively. While Gd₂GeO₅:Tb³⁺ gave bright green cathodoluminescence. In all three phosphors, the energy transfer from Gd³⁺ to activators (e.g. or Bi³⁺) occurred.