Crystal Structure, Photoluminescence, and “Abnormal” High Stability of Ca₃Y(GaO)₃(BO₃)₄: Dy³⁺/Sm³⁺/La³⁺ for n-UV wLEDs

Abstract

In the process of studying newfangled phosphor-converted white-light-emitting diodes (pc-wLEDs), some basic and important objectives of phosphor, i.e., high chemical/thermal stability, color rendering index (CRI), and low correlated color temperature (CCT), should pass muster simultaneously. Herein, for the first time, a series of photoluminescence (PL) color-tunable single-phase Ca3Y(GaO)3(BO3)4: Dy3+/Sm3+/La3+ (CYGB: Dy/Sm/La) phosphors with good dispersivity, crystallinity, and size uniformity have been designed and synthesized via a facile solid-state reaction method. Structurally, based on XRD and Rietveld refinements, the tendentious occupations of Dy/Sm/La on the Y3+ site with a 9-coordinated number (CN) over other cationic sites are in line with the facts that the ionic radius and charge difference of Dy/Sm/La are much closer to Y3+ in 9-CN than Y3+ in 7-CN and Ca2+ in both 9- and 7-CN. Spectrally, thanks to the “cool” white PL from 4f–4f transitions of Dy and red-emitting from Sm, polychromatic PL including “warm” white light with high efficiency could be realized in CYGB: Dy/Sm via the regulation of doping content and energy transfer (ET). Intriguingly, the “abnormal” phenomena of zero-thermal-quenching in the range from room temperature (RT) to 573 K were observed, probably owing to the synergistic effects of electron–phonon coupling, ET, and structural defects. Moreover, by tridoping La3+ to legitimately adjust the site environments, the PL of both Dy/Sm could be further tuned because they all include hypersensitive transitions that are closely related to the crystal field environment. Finally, as a proof-of-concept fabrication, the pc-wLED assembled by a combination of the composition-optimized CYGB: Dy/Sm/La and an n-UV LED chip via remote “capping” packaging shows attractive performances, indicating its potential as an efficient phosphor for n-UV wLEDs.