Concentration dependent spectroscopic behavior of Sm3+-doped sodium fluoro-phosphates glasses for orange and reddish-orange light emitting applications

Abstract

Sodium fluoro-phosphate (NNS) glasses doped with different concentrations of Sm3+ ions have been prepared using conventional melt quenching technique and characterised for their lasing potentialities using spectroscopic techniques such as Raman, optical absorption, emission and emission decay measurements. The structures of glasses were investigated by X-ray diffraction (XRD) and Raman spectroscopy to understand their dependence of structure on composition. Absorption spectrum from near infrared to visible was obtained and the Judd–Ofelt (J-O) intensity parameters (Ω2, Ω4, and Ω6) were determined. Spontaneous emission probabilities of some relevant transitions, branching ratio, and radiative lifetimes of several excited states of Sm3+ have been predicted using intensity J-O parameters. The luminescence intensity decreases with the increase in Sm3+ ion concentration beyond 0.5 mol% and the same was discussed through various energy transfer mechanism which takes place between Sm3+ ions. The lasing parameters like peak stimulated emission cross-section (σep), branching ratios (βR), measured branching ratios (βexp) and radiative lifetime (τrad) for the excited 4G5/2 luminescent level have been calculated, discussed and reported. The measured lifetime (τmeas) of the 4G5/2 excited level is found to be single exponential up to 0.5 mol% and after that it changes into non-exponential for higher concentration and the non-exponential behavior arises due to the energy transfer between the Sm3+ ions through various cross-relaxation channels. The non-exponential decay rates, at higher concentrations, were fitted to Inokuti–Hirayama (IH) model for S = 6 which reveals that the energy transfer process is of dipole–dipole in nature. The R/O intensity ratios have been studied by varying the RE ion concentration and further CIE color chromaticity coordinates have also been calculated to characterize the emission of the prepared glasses. Using the Mc-Cumber method, emission cross-section (σem), Absorption cross-section (σa), and gain cross-section (G(λ)) for the 6F9/2→6H5/2 transition, were calculated.From the emission characteristic parameters of 4G5/2 level, it is concluded that the NNS glasses could be useful for photonic devices like visible lasers, fluorescent display devices and optical amplifiers.