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.