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

Abstract

In this study, we synthesized a series of Ga1.98-xInxO3:0.02Cr3+ 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 4T1, and 4T2 states of Cr3+ ions. This association suggests that photocurrent in this material is influenced not only by valence to conduction band transitions but also by transitions involving Cr3+ dopants. Our investigation of luminescence quenching mechanisms revealed that nonradiative processes were not directly linked to thermally induced relaxation from the excited state 4T2 to the ground state 4A2, as usually suggested in the literature for this type of material. Instead, we linked it to the thermal ionization of Cr3+ ions. Unexpectedly, this process is unrelated to the transfer of electrons from Cr3+ 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 Cr3+-doped oxides, suggesting potential applicability to other transition metal ions and host materials. Finally, we demonstrated the dual-purpose nature of Ga1.98-xInxO3:0.02Cr3+ 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.