PERSISTENT LUMINESCENCE IN Cr-DOPED ZINC GALLOGERMANATE NANOCRYSTALS

Persistent luminescent materials (PeLMs) are characterized by their property to continue emitting light for a prolonged time after the excitation source—such as X-rays, electrons, or ultraviolet/visible radiation—has been removed. Owing to this property, they have attracted considerable interest for numerous applications, including emergency lighting, road safety signaling, bioimaging, photocatalysis, optical data storage, and anti-counterfeiting systems. For several of these applications, nanocrystalline PeLMs are required; however, decreasing the particle size often results in a marked reduction or even a complete suppression of Persistent Luminescence (PeL) at room temperature.¹ An exception to this is for Zn1+xGa2-2xGexO4:Cr (ZGGO:Cr) nanocrystals (NCs). These materials exhibit PeL in the near-infrared region (NIR) lasting several hours after excitation with UV or visible radiation. Experimentally, partial substitution of Ga³⁺ for Ge⁴⁺ significantly modifies the photoluminescence (PL) intensity and the PeL duration. However, the underlying mechanism remains unclear. In this work, we investigate the effect of the progressive substitution of Ga³⁺ with Ge⁴⁺ on both the structural and optical properties. Structural changes are analyzed by X-ray diffraction (XRD), while the optical response is studied through PL, photoluminescence excitation (PLE), and persistent luminescence (PeL) measurements. Preliminary results indicate that the material is typically characterized by NIR emission associated with Cr³⁺, but at higher Ge concentrations (x ≥ 0.4) a significant additional PL contribution emerges in the visible region. Further investigations are currently ongoing to clarify the origin of this effect, but the present results point to a possible strategy for tuning the emission properties of ZGGO:Cr NCs and potentially extending their PeL toward the visible range.