Optical properties of near infrared persistent phosphor CaZnGe2O6: Cr³⁺, M³⁺ (M³⁺ = B³⁺; Al³⁺; Ga³⁺)

Persistent luminescence (PersL) is a phenomenon when a material continues to emit light for a period of time, usually several minutes or hours after the removal of the excitation source. Although it is possible to find several hundred different materials suitable for the observation of PersL in the visible part of the spectrum, only a handful of them is applied to obtain phosphors for near infrared (NIR) emission. In the course of this work, CaZnGe₂O₆: Cr³⁺, M³⁺ (M³⁺ = B³⁺; Al³⁺; Ga³⁺) materials have been synthesized by a melt crystallization method. Photoluminescence (PL) and subsequent PersL of chromium ions in the NIR spectral region, as well as visible PL and PersL of the host material, have been observed. After irradiation with ultraviolet (UV) radiation, a broad NIR PersL band with a maximum around 790 nm and an afterglow time over 1 h has been detected. The addition of B³⁺; Al³⁺; Ga³⁺ increases the overall intensity and duration of PersL. The analysis of PersL decay curves and glow curves of thermally stimulated luminescence (TSL) show multiple trap centres involved in the generation of PersL.