A. Mohan Babu

A study on fluorescence properties of Eu3+ ions in alkali lead tellurofluoroborate glasses

Abstract Glasses with chemical composition of (in mol.%): 26 RF-20 PbO-10 TeO2–43 H3BO3–1 EuO3 (RLTB) were prepared by conventional melt quenching method. The Judd-Ofelt intensity parameters Ω2 and Ω6 were obtained from the absorption intensities of 7F0→5D2 and 7F0→5L6 transitions, respectively. In order to overcome the problem of applicability of Judd-Ofelt analysis at room temperature due to the overlapping of the transitions originating from 7F0 and 7F1 levels of Eu3+ ion, the effect of the thermalization on the population of energy levels was taken into account. The photoluminescence spectra contained five emission bands originating from the 5D0 metastable state to 7FJ(J=0, 1, 2, 3, 4) lower lying states. The decay profiles were found to be single exponential in all the three glasses. The measured lifetimes (τmes) were in good agreement with the calculated lifetimes (τcal) obtained by using the thermally corrected Judd-Ofelt intensity parameters.

Optical and luminescent properties of Sm3+ doped tellurite glasses

Glasses with chemical composition of (62-x) TeO(2)+25 ZnO+8 K(2)O+5 CaO+x Sm(2)O(3) (TZKCSmx; x=0.1, 0.5, 1.0, 1.5 mol%) were prepared by melt quenching technique. The absorption spectrum was recorded in the UV-visible and NIR regions. The oscillator strengths of absorption bands were obtained by measuring the area under the bands. Judd-Ofelt analysis has been carried out to estimate the host dependent J-O intensity Ω(λ) (λ=2, 4, 6) parameters by least squares fitting approach. Photoluminescence spectra recorded in the visible region revealed intense green, orange and red emission bands in all the glasses, corresponding to the (4)G(5/2)→(6)H(5/2), (4)G(5/2)→(6)H(7/2) and (4)G(5/2)→(6)H(9/2) transitions respectively. From the emission spectra and J-O intensity parameters, various radiative parameters were calculated from the excited (4)G(5/2) to the lower lying (6)H(J) (J=5/2, 7/2, 9/2, 11/2) multiplet. Quenching of luminescence with the increase of Sm(3+) ions concentration has been observed. Decay times of excited (4)G(5/2) state decrease with the increase of the Sm(3+) ions concentration. The energy transfer mechanism that leads to the quenching of (4)G(5/2) state lifetime has been discussed. Inokuti-Hirayama (I-H) model was used to evaluate various energy transfer parameters, which are the qualitative indicators for the interaction among Sm(3+) ions.

Optical spectroscopy, 1.06 μm emission properties of Nd3 +-doped phosphate based glasses

Neodymium doped phosphate based glasses with composition of (P2O5+K2O+Al2O3+CaF2) were prepared. The samples were analysed through differential thermal analysis (DTA), Fourier transform infrared (FTIR), absorption, emission and decay measurements. Judd-Ofelt parameters (Ωλ) have been determined from the spectral intensities of absorption bands in order to calculate the radiative parameters like radiative transition probabilities (AR), radiative lifetime (τR) and branching ratios (βR) for the 4F3/2→4I11/2 laser transition of Nd3+ ion. The effective emission bandwidths (Δλeff), experimental branching ratios (βexp) and stimulated emission cross-sections (σe) have been determined from the emission spectrum. The decay curves of the 4F3/2 level exhibited almost single exponential nature for all the Nd3+ ion concentrations.

Sm3+ luminescence in alkali lead tellurofluoroborate glasses

Sm3+- doped alkali lead tellurofluorborate (RLTB) glasses with chemical composition of H3BO3 – RF – PbO -TeO2 – Sm2O3 (R = Li, Na and K) were prepared by conventional melt quenching technique. From the measured absorption spectra, the Judd-Ofelt intensity parameters (Ωλ) have been evaluated. Decay measurements of 4G5/2 metastable state in all the three glass systems were found to be non-exponential. The reasons for non-exponential behaviour of the decay profiles were also discussed based on the Inokuti-Hirayama (I-H) model, confirming the dipole-dipole interaction between the Sm3+ ions.

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.

Role of Yb3+ ions in the IR to visible upconversion of Er3+ ions in LTT glasses

In order to develop efficient visible upconversion lasers and optical fiber amplifiers, the detailed spectroscopic properties of singly doped Er3+ and codoped Er3+-Yb3+ ions in lead tungsten tellurite (LTT) glasses have been investigated. The glasses were prepared by the conventional melt quenching technique. Absorption, visible upconversion spectra and NIR emission spectra were recorded as a function of Yb3+ ions concentrations. Judd-Ofelt (J-O) analysis has been performed for the spectral intensities of Er3+and Er3+-Yb3+ absorption bands. Spontaneous emission probabilities (AR), radiative lifetimes (τR) and branching ratios (βR) were calculated by using the phenomenological Judd-Ofelt intensity parameters. Three strong upconversion emission bands centered at 526, 551 and 665 nm were observed under 980nm excitation, due to the energy transfer process from Yb3+ to Er3+ ions. The green emissions centered at 526 and 551 nm and the red emission at 665 nm are attributed to 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F11/2→ 4I15/2 transitions of Er3+ions respectively. The relative intensity variations of 2H11/2→ 4I15/2, 4S3/2→ 4I15/2 and 4F9/2→ 4I15/2 transitions have been explained on the basis of the increase in the population accumulation rates of 2H11/2 ,4F9/2 and 4S3/2 levels. The peak stimulated emission cross-section (σe) and gain bandwidth parameter (σe×▵λeff) of 4I13/2 → 4I15/2 transition at 1.54 μm for Er3+ and Er3+-Yb3+ ions in LTT glasses have been determined and compared with different glass hosts. The stimulated emission cross-sections (σe) determined by using McCumber theory for the 4I13/2 → 4I15/2 transition are compared with the measured (σe) values obtained from the emission data. The results of these investigations revealed that the lead tungsten tellurite (LTT) glasses could be more useful as promising host materials for the design and development of optical fiber amplifiers and upconversion lasers.

Luminescence properties of Dy3+ doped lithium zinc borosilicate glasses for photonic applications

Different concentrations of Dy3+ ions doped lithium zinc borosilicate glasses of chemical composition (30-x) B2O3 - 25 SiO2 -10 Al2O3 -30 LiF - 5 ZnO - x Dy2O3 (x = 0, 0.1, 0.5, 1.0 and 2.0 mol%) were prepared by the melt quenching technique. The prepared glasses were investigated through X-ray diffraction, optical absorption, photoluminescence and decay measurements. Intensities of absorption bands expressed in terms of oscillator strengths (f) were used to determine the Judd-Ofelt (J-O) intensity parameters Ωλ (λ = 2, 4 and 6). The evaluated J-O parameters were used to determine the radiative parameters such as transition probabilities (AR), total transition probability rate (AT), radiative lifetime (τR) and branching ratios (βR) for the excited 4F9/2 level of Dy3+ ions. The chromaticity coordinates determined from the emission spectra were found to be located in the white light region of CIE chromaticity diagram.