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–xIn_xO₃:0.02Cr³⁺ 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 Ga_1.98–xIn_xO₃:0.02Cr³⁺ 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.