Spectroscopic properties of $\mathrm{Ho}^{3+}$-doped K–Sr–Al phosphate glasses

Abstract

Trivalent holmium-doped K–Sr–Al phosphate glasses ($\mathrm{P}_{2}\mathrm{O}_{5}$–$\mathrm{K}_{2}\mathrm{O}$–SrO–$\mathrm{Al}_{2}\mathrm{O}_{3}$–$\mathrm{Ho}_{2}\mathrm{O}_{3}$) were prepared, and their spectroscopic properties have been evaluated using absorption, emission, and excitation measurements. The Judd–Ofelt theory has been used to derive spectral intensities of various absorption bands from measured absorption spectrum of 1.0 mol% $\mathrm{Ho}_{2}\mathrm{O}_{3}$-doped K–Sr–Al phosphate glass. The Judd–Ofelt intensity parameters ($\varOmega_{\lambda}$, $\times10^{-20}~\mathrm{cm}^{2}$) have been determined of the order of $\varOmega_{2} = 11.39$, $\varOmega_{4} = 3.59$, and $\varOmega_{6} = 2.92$, which in turn used to derive radiative properties such as radiative transition probability, radiative lifetime, branching ratios, etc. for excited states of $\mathrm{Ho}^{3+}$ ions. The radiative lifetimes for the ${}^{5}F_{4}$, ${}^{5}S_{2}$, and ${}^{5}F_{5}$ levels of $\mathrm{Ho}^{3+}$ ions are found to be 169, 296, and 317 μs, respectively. The stimulated emission cross-section for 2.05-μm emission was calculated by the McCumber theory and found to be $9.3\times10^{-2 1}~\mathrm{cm}^{2}$. The wavelength-dependent gain coefficient with population inversion rate has been evaluated. The results obtained in the titled glasses are discussed systematically and compared with other $\mathrm{Ho}^{3+}$-doped systems to assess the possibility for visible and infrared device applications.