K. Pavani

Concentration dependent luminescence characteristics of 5D4 and 5D3 excited states of Tb3+ ions in CFB glasses

Calcium fluoroborate (CFB) glasses doped with different concentrations of Tb3+ ions have been prepared with molar composition of (42-x) B2O3 + 20 CaF2 +15 CaO + 15 BaO + 8 Al2O3 + x TbF3 (x=0.05, 0.1, 0.5, 1.0, 2.0 and 4.0) by melt quenching method. Optical absorption spectrum for 1.0 mol% of Tb3+:CFB glass was recorded in UV-Vis-NIR regions. Radiative parameters such as radiative transition probabilities (AR), radiative lifetimes (τR), radiative branching ratios (βR) for the 5D3 and 5D4 excited states have been calculated by using the Judd-Ofelt parameters (Ωλ=2,4,6). The luminescence spectra recorded for different concentrations of Tb3+ ions in CFB glasses exhibit seven and four bands originating from 5D4 and 5D3 excited states respectively. As the concentration of Tb3+ ions increases the intensities of luminescence peaks originating from 5D4 state increases, whereas, the quenching of intensities has been observed for the emission peaks originating from 5D3 state due to energy transfer through cross-relaxation channel (5D3 : 7F6) → (5D4 : 7F0). The experimental lifetimes of 5D4 state for all the concentrations of Tb3+ ions are equal and exhibit single exponential decay with highest quantum efficiency which confirms that these glasses can be used for high intensity green emission even at high concentrations of Tb3+ ions.

Fluorescence Properties of Pr3+ Doped Calcium Fluoroborate Glasses

Calcium fluoroborate glasses doped with trivalent praseodymium ions have been prepared using melt quenching technique with the molar composition (42-x) B2O3 + 20 CaF2 + 15 CaO + 15 BaO + 8 Al2O3 + x PrF3 (x = 0.05, 0.1, 0.5, 1.0, 2.0 and 4.0). Absorption, fluorescence and lifetime spectra were recorded for the title glasses. Judd-Ofelt intensity parameters Ωt (t = 2, 4 and 6) have been determined for the measured oscillator strengths of the absorption bands by including and excluding the 3H4 → 3P2 hypersensitive transition. From the intensity parameters spontaneous emission probabilities (AR), excited state radiative lifetimes (τR) and branching ratios (βR) were calculated. Fluorescence quenching is observed in all the peaks and is explained by energy transfer mechanisms. Using the fluorescence spectra stimulated emission cross section (σe) for all emission transitions have been estimated. Energy transfer processes were also explained to emphasize the quenching of fluorescence intensity of certain emission transition. Based on the results, the utility of Pr3+ doped calcium fluoroborate glasses as laser active materials as well as wave guides in the visible region is discussed.

Optical absorption and fluorescence properties of Dy3+: SFB glasses

This paper presents the preparation and spectroscopic characterization of Dy3+-doped sodium fluoroborate (SFB) glasses of the type (50-x) B2O3 + 25 Na2O + 10 CaF2 + 10 AlF3 + 5 LaF3 + x DyF3 (x = 0.01, 0.1, 0.5,1.0, 2.0 and 4.0 mol%). By measuring the area under absorption bands, the experimental oscillator strengths are determined. The Judd-Ofelt (J-O) intensity parameters Ωλ (λ = 2, 4, 6) are evaluated by the least square fit method. These phenomenological parameters are used to predict luminescence properties of the lanthanide ions in SFB glasses. Photoluminescence spectra and lifetimes of 4F9/2 level of Dy3+ ions in these glasses have been measured by exciting with 348 nm line of xenon flash lamp. The measured decay curves exhibit single exponential at lower concentrations of 0.01, 0.1, 0.5 and 1.0 mol% and non-exponential at higher concentrations of 2.0 and 4.0 mol%. The predicted τR and (βR values of 4F9/2 transition are compared with the experimentally measured values. From the magnitude of stimulated emission cross sections (σe), branching ratios (βm), multiphonon relaxation rates (WMP), the most potential laser transitions are identified and the utility of these glasses as laser active material is discussed.

Er 3+ doped calcium fluoroborate glasses for fiber amplifiers

Calcium fluoroborate glasses doped with Er₂O₃ (CFBEr) were prepared by the conventional melt quenching technique with molar compositions of (42-x) B₂O₃ + 20 CaF₂ + 15 CaO + 15 BaO + 8 Al₂O₃ + x Er₂O₃ (x = 0.05, 0.1, 0.5, 1.0, 2.0 and 4.0). Optical absorption spectrum in the region 250-2500 nm was recorded by using UV-Vis-NIR spectrophotometer for 1.0 mol % Er₂O₃ doped CFBEr10 glass. The absorption spectrum revealed thirteen absorption bands corresponding to transitions originating from ground (⁴I_15/2) state of erbium ions to various excited states. Judd-Ofelt (J-O) analysis has also been carried out from the experimental oscillator strengths (f_exp) to evaluate the JO intensity parameters (Ω₂, Ω₄ and Ω₆) and the calculated oscillator strengths (f_cal). Radiative parameters like radiative transition probabilities (A_R), total radiative transition probabilities (A_T), branching ratios (β_R) and radiative lifetimes (τ_R) were calculated for different excited states of Er³⁺ ion in CFB glasses. McCumber theory has been adapted to predict the emission cross-section of the NIR emission peak (⁴I_13/2 → ⁴I_15/2) at 1.53 μm. NIR luminescence spectra were recorded for all the glasses by exciting the samples with 980 nm diode laser and compared with that of the predicted emission cross-section. Variation of intensity as well as FWHM of the NIR emission transition has been studied for the utilization of these glasses in fiber amplifiers.