Figure 3. Anti-Stokes luminescence kinetics.

Photoluminescence decay in dependence on duration of excitation (a. constant excitation intensity 0.03 W) and excitation intensity (b. constant excitation duration 2 min) for excitation with a 980 nm laser diode (LD) and monitoring the emission intensity at a wavelength of 700 nm. Before measurements, effective optical charging of the probe can be done by UV-vis light for 5 min, the measurements were taken at the interval of 24 hours after charging.