Site Occupancy and Near‐Infrared Luminescence in Ca₃Ga₂Ge₃O₁₂: Cr³⁺ Persistent Phosphor

The near‐infrared (NIR) luminescence properties of Cr³⁺ activated Ca₃Ga₂Ge₃O₁₂ (CGGG) are studied under ultraviolet and visible light excitation. Three types of Cr³⁺ centers associated with ⁴T₂–⁴A₂ transition resulting in the emissions located at 650–1100 nm are identified in all Cr³⁺‐doped samples. Thanks to the occupancy of three nonequivalent sites in CGGG, NIR luminescence is observed peaking at about 749, 803, and 907 nm, respectively. The influence of crystal field on site occupancy is studied, the relation between site occupancy and the NIR luminescence is addressed, and the energy transfer process among Cr³⁺ sites and the decay behaviors for Cr³⁺ in different sites are evaluated. It is found that a superior NIR/persistent luminescence comes from the traps that Cr³⁺ enters the Ga³⁺ site. The results are of benefit to investigate Cr³⁺‐activated persistent phosphors.