Anti-stokes luminescence in LiYF$_{4}$ : Ho$^{3+}$, Yb$^{3+}$ ceramics excited at 1.93 $\mu$m

Conversion of IR radiation of a Tm:YAP laser with a wavelength of 1930 nm into visible light by ceramics of composition LiY$_{(1-x-y)}$Ho$_{x}$, Yb$_{y}$, where $х$ = 1–5 mol% and $y$ = 0–15 mol%, is demonstrated. It is shown that the threshold power density of IR light visualization decreases with increasing concentration of Ho$^{3+}$ ions, while additional doping of ceramic samples with Yb$^{3+}$ ions changes the anti-Stokes luminescence spectrum. The threshold power density of visualization of the Tm:YAP laser radiation decreases with increasing concentration of holmium ions and is $I_{\mathrm{thr}}$ $\approx$ 0.8 W cm$^{-2}$ in the samples of composition LiYF$_{4}$ : 5%Ho$^{3+}$–15%Yb$^{3+}$.