Study of Anti-Stokes Luminescence of ZBLAN:Нo³⁺ Ceramics Excited at 1908 nm

Abstract

Visualization of IR radiation of a Tm:YLF laser with a wavelength of 1908 nm in 53ZrF₄–20BaF₂–3LaF₃–1HoF₃–3AlF₃–20NaF (mol %) ceramic samples is studied. The luminescence spectra of Но³⁺-doped ZBLAN ceramics exhibit bands in the regions of 540, 650, and 900 nm, which correspond to the ⁵S₂ → ⁵I₈, ⁵F₅ → ⁵I₈, and ⁵I₅ → ⁵I₈ transitions, the red band (650 nm) being most intense. The population of the upper levels of these transitions can be explained using the cascade excitation mechanism. A visualization model is developed based on balance equations for populations of the upper energy states of Но³⁺ ions. The population distributions are numerically estimated as functions of the excitation intensity. The obtained time dependences of the populations of the ⁵S₂ and ⁵F₅ states correlate with the experimental time dependences of the luminescence intensity at the ⁵S₂ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions upon pulsed excitation. The threshold power density of a Tm:YLF laser at which luminescence of the ceramic samples was observed was ~2 W/cm².