Flame-Made Cr3+-Doped Ga2O3 Nanoparticles Toward Cryogenic Thermometry and Near-Infrared LEDs

As an emerging ultrawide bandgap semiconductor, Ga2O3 nanoparticles (NPs) have garnered significant attention across various fields due to their high thermal and chemical stability. Conventional synthesis methods for Ga2O3 NPs, such as high-temperature solid-state reactions and hydrothermal processes, encounter challenges including complex procedures, limited scalability, and production of large particle sizes. In this study, we develop a straightforward approach to synthesize phase-pure, nanosized Ga2O3 NPs through flame spray pyrolysis, followed by an annealing treatment. By the incorporation of trivalent chromium ions (Cr3+) into the Ga2O3 NPs, it achieves intensive near-infrared (NIR) luminescence, specifically the R lines associated with the 4T2 → 4A2 and 2E → 4A2 transitions. These R lines are sensitive to cryogenic temperatures due to their relatively small energy difference. The synthesized Ga2O3 NPs demonstrate excellent ratiometric thermometric performance within the temperature range of 83–213 K, achieving a maximum relative sensitivity of 3.35% K–1 at 83 K based on the Boltzmann distribution of the luminescent thermometer. Furthermore, an efficient NIR phosphor-converted LED (pc-LED) device is fabricated by employing Cr3+-doped Ga2O3 NPs, which are excited by using a blue LED chip. This NIR pc-LED is subsequently applied in night vision illumination and anticounterfeiting detection.