Tb3+ and Ce3+ as a Functional Couple for Enhanced Luminescence in YAG Ceramics for X-Ray Imaging and High-Power White LEDs and Laser Diodes

Abstract

The exposure of luminescent materials to X-ray radiation and high-power laser excitation results in significant heating, leading to thermal quenching and a corresponding reduction in phosphor efficiency. This study aimed to address this limitation by enhancing material efficiency while maintaining high thermal stability. YAG:Ce,Tb transparent ceramics were successfully fabricated via vacuum reactive sintering method, with moderate concentrations of Tb3+ ions (1, 5 and 10 at.%) codopants. These ceramics exhibited a dense microstructure without micropores, achieving high transparency of 77–80% at 900 nm. The incorporation of Tb3+ ions, is evidenced by the systematic increase in lattice constants from 12.608 Å (YAG:Ce) to 12.615 Å (YAG:Ce,Tb10%) in accordance with Vegard's law. The phonon-assisted Ce3+↔Tb3+ bidirectional resonance mechanism, which facilitated energy transfer between Ce3+ and Tb3+ ions, was observed. The optimal transfer rate was observed at approximately 480 K. Beyond this temperature, the rate progressively accelerated, leading to accelerated decay times. Notably, YAG:Ce,Tb10% ceramics demonstrated a two-fold increase in radioluminescence intensity compared to uncodoped YAG:Ce ceramics. This substantial improvement in luminescence performance highlights the potential of YAG:Ce,Tb ceramics as highly efficient phosphors for X-ray imaging applications, offering enhanced brightness and energy transfer efficiency under high-temperature operating conditions. The Tb3+ codoping also enhanced Ce3+ emission, allowing for tuning of the correlated color temperature to a maximum of 6013 K, while maintaining a stable color rendering index of 69–73 and luminous efficacy of ~123 lm/W. It was shown that the luminous efficacy was not a constant parameter, but depended on the excitation laser power, initially increasing with power up to 0.5 W and then saturating. These results establish YAG:Ce,Tb transparent ceramics as highly promising materials for white LEDs due to their good thermal stability, tunable optical properties, and enhanced luminescence performance.

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