Study of multicomponent fluoro-phosphate based glasses: Ho³⁺ as a luminescence center

The multicomponent 49.5P₂O₅–10AlF₃–10BaF₂–10SrF₂–10PbO–10M (M=Li₂O, Na₂O, K₂O, ZnO and Bi₂O₃) glasses doped with 0.5 mol% holmium were prepared by melt quenching technique. Their thermal behavior was examined from differential scanning calorimetry (DSC). It is found that bismuth fluoro-phosphate glass matrix has good thermal stability. Their structures were characterized by the X-ray diffraction with SEM analysis, fourier transform infrared (FTIR), Raman spectroscopy and magic angle spinning (MAS) nuclear magnetic resonance (NMR) techniques. It was found that the phosphate network of these glasses was composed mainly of Q² and Q³ phosphate tetrahedral units. The Judd–Ofelt parameters (J–O) (Ω₂, Ω₄ and Ω₆) were evaluated from the intensities of the energy levels through optical absorption spectra. The most intense transitions are observed in the visible region of the spectrum. It is observed that the transition ⁵I₈→⁵G₆ is the hypersensitive transition for Ho³⁺ ion. With these J–O parameters, various radiative properties like the probabilities of radiative transitions, radiative lifetimes and branching ratios have been calculated for different fluoro-phosphate glasses. The luminescence kinetics from excited holmium levels have been studied upon selective excitation through photoluminescence measurements. Holmium produces two visible laser emissions i.e. one is green (⁵F₄(⁵S₂)→⁵I₈ ) and another one is red (⁵F₅→⁵I₈). The lifetimes of these levels have been experimentally determined through decay profile studies. The above results suggest that the prepared bismuth fluoro-phosphate glass system could be a suitable candidate for using it as a green laser source (⁵F₄(⁵S₂)→⁵I₈ ) in the visible region of the spectrum. - Highlights: • Holmium doped different fluoro-phosphate glasses were prepared and characterized. • Structural, thermal and spectroscopic properties have been studied. • Prominent green laser transition Ho³⁺:(⁵F₄(⁵S₂)→⁵I₈ ) is observed at 535 nm. • Among all FP glasses, bismuth fluoro-phosphate glass has good properties.