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

The near‐infrared (NIR) luminescence properties of Cr 3+ activated Ca 3 Ga 2 Ge 3 O 12 (CGGG) are studied under ultraviolet and visible light excitation. Three types of Cr 3+ centers associated with 4 T 2 – 4 A 2 transition resulting in the emissions located at 650–1100 nm are identified in all Cr 3+ ‐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 Cr 3+ sites and the decay behaviors for Cr 3+ in different sites are evaluated. It is found that a superior NIR/persistent luminescence comes from the traps that Cr 3+ enters the Ga 3+ site. The results are of benefit to investigate Cr 3+ ‐activated persistent phosphors.