Strong f ‐ f Excitation and Bright Red Emission in Cd 4 Gd 1‐ x Eu x O(BO 3 ) 3 (0≤ x ≤1): Near‐UV LED Pumped Red Phosphor with Low Thermal Quenching

: Searching efficient red phosphors under near-UV or blue light excitation is practically important to improve the current white light-emitting diodes (WLEDs). Eu2+ - and Mn4+ -based red phosphors have been extensively studied. Here we proposed that Eu3+ is also a promising activator when it resides on a noncentrosymmetric coordination site. We proved that Cd4 GdO(BO3 )3 is a good host, which has a significantly distorted coordination for Eu3+ . A careful crystallographic study was performed on the solid solutions of Cd4 Gd1-x Eux O(BO3 )3 (0≤x≤1) by Rietveld refinements. The as-doped Eu3+ cations locate at the Gd3+ site and are well separated by CdO8 , CdO6 and BO3 groups; thus, only a slight concentration quenching was observed at ≈80 atom % Eu3+ . Most importantly, the parity-forbidden law of 4f-4f transitions for Eu3+ are severely depressed, thus the absorptions at ≈393 and ≈465 nm are remarkable. Cd4 Gd0.2 Eu0.8 O(BO3 )3 can be pumped by a 395 nm LED chip to give a bright red emission, and when mixed with other commercial blue and green phosphors, it can emit the proper white light (0.3657, 0.3613) with a suitable Ra ≈87 and correlated colour temperature ≈4326 K. In-situ photoluminescence study indicated the low thermal quenching of these borate phosphors, especially under 465 nm excitation. Our case proves the practicability to develop near-UV excited red phosphors in rare-earth-containing borates.