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.     

Structural, optical and thermal investigations on Dy doped NaF–Li2O–B2O3 glasses

Structural, optical and thermal properties of Dy³⁺ doped lithium fluoroborate glasses have been studied for various concentrations of Dy³⁺ from 0.5 to 5 wt%. The XRD studies confirm the amorphous nature of the glasses while the FTIR spectra reveal the presence of BO₃ and BO₄ local structural units. The UV–VIS–NIR absorption studies were carried out to calculate the bonding parameters ( and δ), to identify the ionic/covalent nature of the glasses. The JO parameters, experimental and theoretical oscillator strengths were also determined and reported. The luminescence spectra have been studied to determine the radiative transition probability (A), stimulated emission cross section () and the experimental and calculated branching ratios (β_R) for the excited levels that include ⁴F_9/2→⁶H_11/2, ⁶H_13/2, and ⁶H_15/2 transitions. The variation of optical properties with varying concentrations of dysprosium oxide content in the glasses are reported and discussed. The thermal behavior of Dy³⁺ doped lithium fluoroborate glasses have been reported by recording DSC thermograms.     

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.     

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.     

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.     

Structural and luminescence properties of Dy3+ ion in strontium lithium bismuth borate glasses

Different concentrations of dysprosium doped strontium lithium bismuth borate (SLBiB) glasses were synthesized by the conventional melt quenching method and characterized through X-ray diffraction, Raman, absorption and visible luminescence spectroscopies. These Dy³⁺ doped glasses are studied for their utility for white light emitting diodes. X-ray diffraction studies revealed amorphous nature of the studied glass matrices. Coexistence of trigonal BO₃ and tetrahedral BO₄ units was evidenced by Raman spectroscopy. From the absorption spectra, Judd–Ofelt (J–O) intensity parameters, Ω_λ (λ=2, 4 and 6), have been calculated. The hypersensitivity of the transition, ⁶H_15/2→⁶F_11/2 of Dy³⁺ has been discussed based on the magnitude of Ω₂ parameter. Using J–O intensity parameters, several radiative properties such as spontaneous transition probabilities (A_R), radiative branching ratios (β_R) and radiative lifetimes (τ_R) have been determined. From the emission spectra, a strong blue emission that corresponds to the transition, ⁴F_9/2→⁶H_15/2, was observed and it also shows combination of blue, yellow and red emission bands for these glasses. In addition to that, white light emission region have been observed from these studies.     

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.     

Absorption and fluorescence studies of Sm ions in lead containing sodium fluoroborate glasses

Lead containing calcium zinc sodium fluoroborate glasses (LCZSFB) with molar composition of 20PbO+5CaO+5ZnO+10NaF+(60−x) B₂O₃+x Sm₂O₃, (x=0.1, 0.25, 0.5, 1.0 and 2.0 mol%) were prepared and investigated by the XRD, FTIR, optical absorption, photoluminescence and decay curve analysis. Judd-Ofelt theory was applied to the experimental oscillator strengths to evaluate the phenomenological J-O intensity parameters Ω_λ (λ=2, 4 and 6). Using the J-O intensity parameters as well as from the emission and decay measurements, various radiative parameters such as transition probabilities (A_R), radiative lifetimes (τ_R), measured lifetimes (τ_m), calculated branching ratios (β_R), measured branching ratios (β_m), effective bandwidth (Δλ_eff) and stimulated emission cross sections σ(λ_p) have been calculated for the excited ⁴G_5/2 luminescent level. The nature of decay curves of ⁴G_5/2 level for different Sm³⁺ ion concentrations in all LCZSFB glasses has been analyzed and the lifetimes are noticed to decrease with increase of concentration. The concentration quenching has been attributed to the energy transfer through the cross-relaxation between Sm³⁺ ions. Based on these results, the utility of Sm³⁺ ions doped lead containing fluoroborate glasses as laser active materials in the visible region is discussed.     

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.     

Concentration dependent Eu3+ doped boro-tellurite glasses—Structural and optical investigations

Eu³⁺ doped boro-tellurite glasses with the chemical composition (40?x)B₂O₃+30TeO₂+15MgO+15K₂O+xEu₂O₃ (where x=0.01, 0.1, 1, 2 and 3 wt%) have been prepared by following the conventional melt quenching technique. Structural and optical behavior of the prepared Eu³⁺ doped boro-tellurite glasses were studied and compared with reported literature. The XRD pattern confirms the amorphous nature and the FTIR spectral studies explore the presence of BO stretching vibrations, O₃BOBO₃ bond bending vibrations along with the bending vibration of TeOTe linkages in the prepared glasses. Through the optical absorption spectra, bonding parameters ($\overline{\beta },\delta$) were calculated to identify the ionic/covalent nature of the glasses. Judd–Ofelt (JO) parameters have been calculated from the luminescence spectral measurements. The JO parameters (Ω_λ, λ=2, 4 and 6) were used to calculate the radiative properties like transition probability (A), stimulated emission cross-section (${\sigma }_P^E$), radiative lifetime (τ_rad), and branching ratios (β_R) for the ⁵D₀→⁷F_J (J=0, 1, 2, 3 and 4) emission transitions of the Eu³⁺ ions. The local site symmetry around the Eu³⁺ ions were calculated through the luminescence intensity ratio (R) of the ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁ transitions. The experimental lifetime of the ⁵D₀ level in the Eu³⁺ doped boro-tellurite glasses has also been calculated and compared with similar Eu³⁺ glasses. The lifetime of the ⁵D₀ level is found to be less than the reported glasses and it may be due to the presence of OH^? groups in the prepared glasses. The Optical band gap (E_opt), band tailing parameter (B) and the Urbach energy (ΔE) values of the prepared glasses were calculated from the absorption spectral measurements and the results were discussed and reported.     

Optical transitions of Dy in tellurite glass: observation of upconversion

Dy³⁺ doped tellurite glasses were prepared and its optical absorption, fluorescence and upconversion have been studied. The absorption data has been used to calculate the Judd-Ofelt parameters, oscillator strengths along with transition probability, branching ratio, etc. The lifetime of the level is found to be 0.66 ms for 1.0 mol% of Dy³⁺ doped in tellurite glass. NIR to visible upconversion has been observed at room temperature. The increase in upconversion luminescence at lower temperature indicates that upconversion is not due to a thermally activated process. The quantum efficiency of the transition is found to be ∼0.17 and the upconversion efficiency is ∼0.022. The strong dependence of the upconversion efficiency on the Dy³⁺ concentration reveals that the upconversion is due to energy transfer interaction.     

Emission characteristics of Dy3+ ions in lead antimony borate glasses

Glasses with the composition 30PbO–25Sb₂O₃–(45?x)B₂O₃–xDy₂O₃ for x=0 to 1 were prepared in steps of 0.2 by the melt-quenching method. Various physical parameters, viz., density, molar volume, and oxygen packing density, were evaluated. Optical absorption and luminescence spectra of all the glasses were recorded at room temperature. From the observed absorption edges optical band gap, the Urbach energies are calculated; the optical band gap is found to decrease with the concentration of Dy₂O₃. The Judd–Ofelt theory was applied to characterize the absorption and luminescence spectra of Dy³⁺ ions in these glasses. Following the luminescence spectra, various radiative properties, like transition probability A, branching ratio β and the radiative life time τ for different emission levels of Dy³⁺ ions, have been evaluated. The radiative lifetime for the ⁴F_9/2 multiplet has also been evaluated from the recorded life time decay curves, and the quantum efficiencies were estimated for all the glasses. The quantum efficiency is found to increase with the concentration of Dy₂O₃.     

Structural and photoluminescence properties of Dy3+ doped different modifier oxide-based lithium borate glasses

Structural and photoluminescence properties of Dy³⁺ doped lithium fluoro-borate glasses with the compositions Li₂B₄O₇–BaF₂–NaF–MO (where M=Mg, Ca, Cd and Pb), Li₂B₄O₇–BaF₂–NaF–MgO–CaO and Li₂B₄O₇–BaF₂–NaF–CdO–PbO have been investigated through XRD, FTIR, optical absorption, emission and decay measurements. 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 probabilities (A_T), branching ratios (β_r) and stimulated emission cross sections (σ_p) for all emission levels of Dy³⁺ ion in different lithium fluoro-borate glass matrices. From the emission spectra, chromaticity color coordinates have been calculated and indicated emission color for all glass matrices. The nature of decay profiles of ⁴F_9/2 state of Dy³⁺ in all the glass matrices are analyzed.     

EPR study of Mn-implanted single crystal plates of TiO2 rutile

Single crystals of Mn-implanted TiO₂ rutile have been investigated by electron paramagnetic resonance (EPR) technique at room temperature. We have observed an EPR signal on Mn⁴⁺ ions (S=) in the manganese-implanted single crystal TiO₂ plates. Besides, weaker EPR signals due to Fe³⁺(S=, L=0) and Cr³⁺(S=) ions have also been observed. Characteristic six-line splitting of the manganese EPR lines due to hyper-fine interaction with ⁵⁵Mn nuclei (spin I=) has also been observed. Analysis of the EPR spectra shows that the manganese, iron and chromium ions substitute for Ti⁴⁺ ions in the TiO₂ rutile host. Two structurally equivalent groups of the centers have been observed in the EPR spectra in correspondence with two octahedral positions of the Ti ions in the rutile structure. Spin Hamiltonian parameters for the crystal field of orthorhombic symmetry on the Mn⁴⁺, Fe³⁺ and Cr³⁺ centers have been obtained as result of computer modelling.     

Van Vleck paramagnetism of the trivalent Eu ions

Magnetic susceptibilities of Eu₂O₃, EuF₃ and EuBO₃ have been measured over the wide temperature range 5-650 K. The Van Vleck paramagnetism, with the ground state of ⁷F₀ (S=3, L=3), has been investigated comprehensively. The temperature independent paramagnetism emerges manifestly below approximately 100 K. The variation of the susceptibility with temperature for EuBO₃ is in satisfactory agreement with the coupling constant , where the spin-orbit interaction is λL·S for the Russell-Saunders coupling on the basis of Van Vleck theory with one parameter λ. The value of can fit the susceptibility data of EuF₃. The deviation from the theory arises in Eu₂O₃. This discrepancy originates mainly from the influence of the crystalline field. Susceptibility of Gd₂O₃, having the ground state of ⁸S_7/2 (S=7/2, L=0), is also presented as a magnetic standard compound in comparison with these results.     

Specific heat of EuIn2P2 at high magnetic fields

We have carried out specific heat measurements on EuIn₂P₂ at high magnetic fields perpendicular to the c-axis in the hexagonal crystal structure in order to understand its thermal properties. The temperature dependence of the specific heat exhibits a clear λ-type anomaly due to a magnetic transition at , indicating that the magnetic transition is of second-order. The λ-type anomaly becomes markedly broader with increasing the magnetic field. This remarkable field-dependence is consistent with the results of previous magnetization measurements which suggest that Eu²⁺ magnetic moments align ferromagnetically perpendicular to the c-axis below T_C. In addition, a hump in the specific heat is observed around 7 K, which can be ascribed to the Zeeman splitting of the Eu²⁺ multiplet by internal magnetic fields.