Advancing Near-Infrared Light Sources: Enhancing Chromium Emission through Cation Substitution in Ultra-Broadband Near-Infrared Phosphors

Abstract

The growing interest in the use of near-infrared (NIR) radiation for spectroscopy, optical communication, and medical applications spanning both NIR-I (700-900 nm) and NIR-II (900-1700 nm) has driven the need for new NIR light sources. NIR phosphor-converted light-emitting diodes (pc-LEDs) are expected to replace traditional lamps mainly due to their high efficiency and compact design. Broadband NIR phosphors activated by Cr³⁺ and Cr⁴⁺ have attracted significant research interest, offering emission across a wide range from 700 to 1700 nm. In this work, we synthesized a series of Sc_2(1-x)Ga_2xO₃:Cr^3+/4+ materials (x = 0-0.2) with broadband NIR-I (Cr³⁺) and NIR-II (Cr⁴⁺) emission. We observed a substantial increase in the intensity of Cr³⁺ (approximately 77 times) by incorporating Ga³⁺ ions. Additionally, our investigation revealed that energy transfer occurred between Cr³⁺ and Cr⁴⁺ ions. Configuration diagrams are presented to elucidate the behavior of Cr³⁺ and Cr⁴⁺ ions within the Sc₂O₃ matrix. We also observed a phase transition at a pressure of 20.2 GPa, resulting in a new unknown phase where Cr³⁺ luminescence exhibited a high-symmetry environment. Notably, this study presents the pressure-induced shift of NIR Cr⁴⁺ luminescence in Sc_2(1-x)Ga_2xO₃:Cr^3+/4+. The linear shifts were estimated at 83 ± 3 and 61 ± 6 cm^-1/GPa before and after the phase transition. Overall, our findings shed light on the synthesis, luminescent properties, temperature, and high-pressure behavior within the Sc_2(1-x)Ga_2xO₃:Cr^3+/4+ materials. This research contributes to the understanding and potential applications of these materials in the development of efficient NIR light sources and other optical devices.