Improving Thermal Stability of Eu3+ Luminescence via High-Concentration Terbium Doping in NaGd2Ga3Ge2O12 Garnet

Phosphors for white light-emitting diodes (WLEDs) would suffer from inadequate luminescent thermal stability, especially at high temperatures, affecting both the reliability and lifespan of devices. Thus, the development of phosphors with excellent thermal stability is a crucial task. By use of a high-temperature solid-state reaction method, a series of Tb3+ and Eu3+ codoped NaGd2Ga3Ge2O12 (abbreviated as NGGGO) phosphors has been successfully synthesized. With an appropriate doping concentration of Tb3+ and Eu3+, the NGGGO:Tb3+,Eu3+ phosphors can provide color tunable emissions; simultaneously, the energy transfer (ET) efficiency from Tb3+ to Eu3+ can reach nearly 100%. Notably, high-concentration Tb3+ doping in NGGGO could induce oxygen vacancies, giving significant enhancement on the thermal stability of Eu3+ luminescence. For the NGGGO:60% Tb3+,1.6% Eu3+ phosphor, the emission intensity of Eu3+ at 450 K remained even higher than that observed under room-temperature conditions. By use of the as-synthesized phosphor as a red emission converter, a near-ultraviolet pumped WLED device can be fabricated. Under a driving current of 20 mA, the device exhibits high color rendering index (CRI) ∼ 89, low correlated color temperature (CCT) ∼ 4603 K, and bright white light with CIE chromaticity coordinates of (0.3569, 0.3587), which demonstrates the potential of NGGGO:Tb3+,Eu3+ phosphors in WLED application.