Eu2+/Eu3+-doped oxyfluoride glass-ceramics for modular warm white emission

Abstract

White light-emitting diodes (WLEDs), which typically combine a yttrium aluminum garnet doped with Ce³⁺ (YAG:Ce) with a blue LED, have been widely applied as illumination devices because of their high efficiency and long-term stability. However, the color of YAG:Ce-based WLEDs is cold and the color rendering index (CRI) is low due to the lack of a red component in the spectra. Here, we have successfully fabricated Eu-doped oxy-fluoride glass-ceramics (GCs) containing Na₅Gd₉F₃₂ and NaAlSiO₄ nano- and micro-crystals via melting-quenching and post-annealing with aluminum powder doping processes for synthesizing mono-host warm WLEDs. Annealing at 640 °C led to the two crystalline phases precipitated in the amorphous glass matrix, and the GCs exhibited broad emission from 430–600 nm and sharp orange-red emissions around 610 nm originating from Eu²⁺ and Eu³⁺ ions co-excited by a UV source. The GCs excited with an InGaN UV chip show adjustable warm white emission, while the correlated color temperature could be tuned via aluminum powder doping to <3500 K, with a CRI of around 78 and a photoluminescence quantum yield of >46%. Moreover, we examined the laser-driven photoluminescence properties of the prepared GCs, and the results show that the Eu-doped GCs exhibit both a high luminous saturation threshold and color stability.