Optical properties of holmium-doped β″-alumina

Abstract

Ho³⁺-doped β″-aluminas have been prepared over a wide range of concentrations by the ion-exchange method. The absorption, emission and excitation spectra of these materials have been determined in combination with fluorescence lifetime measurements. The absorption spectra were characterized by extremely strong hypersensitive transitions that were relatively independent of polarization while the other transitions exhibited higher oscillator strengths in π polarization. A Judd–Ofelt analysis was performed and various parameters were calculated for the different absorption and emission bands including intensity parameters, spontaneous emission probabilities and branching ratios. The stimulated emission cross-section was calculated for the 2.1 µm band of Ho³⁺ : β″-alumina at 77 K and was found to be 1 × 10^–20 cm² with a quantum efficiency of 25%. This relatively low value for efficiency is associated with multiphonon relaxation processes in the lattice.