Photoelectric Studies as the Key to Understanding the Nonradiative Processes in Chromium Activated NIR Materials.

In this study, we synthesized a series of Ga 1.98- x In x O 3 :0.02Cr 3+ materials with varying x values from 0.0 to 1.0, focusing on their broadband near-infrared emission and photoelectric properties. Interestingly, photocurrent excitation spectra exhibited behavior consistent with the absorption spectra, indicating the promotion of carriers into the band structure by the 4 T 1 , and 4 T 2 states of Cr 3+ ions. This association suggests that photocurrent in this material is influenced not only by valence to conduction band transitions but also by transitions involving Cr 3+ dopants. Our investigation of luminescence quenching mechanisms revealed that nonradiative processes were not directly linked to thermally induced relaxation from the excited state 4 T 2 to the ground state 4 A 2 , as usually suggested in the literature for this type of material. Instead, we linked it to the thermal ionization of Cr 3+ ions. Unexpectedly, this process is unrelated to the transfer of electrons from Cr 3+ impurities to the conduction band but is associated with the formation of holes in the valence band. This study provided novel evidence of luminescence quenching via the hole-type thermal quenching process in Cr 3+ -doped oxides, suggesting potential applicability to other transition metal ions and host materials. Finally, we demonstrated the dual-purpose nature of Ga 1.98- x In x O 3 :0.02Cr 3+ as a practical emitter for NIR-pc-LEDs and effective photocurrent for UV detectors. This versatility underscores these materials' practicality and broad application potential in optoelectronic devices designed for near-infrared and ultraviolet applications.