Spectroscopic characteristics of Sm³⁺ doped alkaline earth potassium titanium phosphate glasses

Abstract

The paper reports on the preparation and characterization of Sm³⁺ doped alkaline earth potassium titanium phosphate (RKTP) glasses with molar composition of 24(NaPO₃)₆ + 30KH₂PO₄ + 25TiO₂ + 20RCl₂ + 1Sm₂O₃ (R=Mg, Ca & Sr). Optical absorption spectra in the UV-VIS-NIR region reveal twelve absorption bands and are assigned to different transitions arising from the ⁶H_5/2ground state. The energy level structure of Sm³⁺ (4f⁵) has been analyzed using the free-ion Hamiltonian model. The root mean square deviations between the experimental and calculated energies of Sm³⁺ doped MgKTP, CaKTP and SrKTP glasses are 44, 35 and 56 cm^-1 respectively and are comparable with the earlier reports. By measuring the areas under the absorption peaks, the experimental oscillator strengths are calculated and the phenomenological JO-intensity parameters (Ω₂, Ω₄ and Ω₆) have been determined with the help of least-squares fitting approach. These parameters exhibit a similar trend as Ω₂>Ω₆>Ω₄ in all the three glasses. The evaluated JO parameters are then used to calculate the excited ⁴G_5/2 level radiative properties such as radiative transition probabilities (<i style="">A</i>_R), branching ratios (β_R) and lifetimes (<img src='/image/spc_char/tow.gif'> _R). The emission spectra recorded by exciting with 476 nm shows four peaks at 563, 599, 649 and 714 nm and are assigned to ⁴G_5/2→ ⁶H_5/2, ⁶H_7/2, ⁶H_9/2,⁶H_11/2 respectively. The experimentally observed decay profiles of the ⁴F_5/2level of Sm³⁺ are found to be single exponential yielding the lifetimes (<img src='/image/spc_char/tow.gif'> _mes) 2330, 1750 and 2320 μs in MgKTP, CaKTP and SrKTP glasses respectively, which are comparable with the calculated lifetimes (<img src='/image/spc_char/tow.gif'> _R) obtained from the Judd-Ofelt theory.