Mid-infrared emissions from Ho3+ in Ga2S3-GeS2-Sb2S3 glass

Emission properties were investigated in the infrared region for Ga2S3-GeS2-Sb2S3 glasses doped with Ho3+. We performed Judd–Ofelt analysis and lifetime measurements of the 5I4, 5I5, and 5I6 levels, which are the initial levels of the mid-infrared emissions between 3 to 5 μm of Ho3+. The quantum efficiencies reached approximately 18%, 64%, and ∼100% for the 5I4, 5I5, and 5I6, respectively. Population analyses were carried out from the relative intensities of the emissions in the near-infrared region. We investigated the dependences on the Ho3+ ion concentration of the population ratio of the initial levels to the final levels, [initial]/[final], of the mid-infrared emissions. The population ratio of [5I5]/[5I6] decreased with increase of the Ho3+ concentration while those of [5I4]/[5I5] and [5I6]/[5I7] increased. Particularly, the former, [5I4]/[5I5], rapidly increased because of the strong concentration quenching of the 5I5 level through cross relaxation. It was found that the population inversion for the 4.8 μm emission due to the transition, 5I4→5I5, was achieved at high Ho3+ concentration in the present experiments.