Strong f-f Excitation and Bright Red Emission in Cd Gd Eu O(BO ) (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). Eu - and Mn -based red phosphors have been extensively studied. Here we proposed that Eu is also a promising activator when it resides on a noncentrosymmetric coordination site. We proved that Cd GdO(BO ) is a good host, which has a significantly distorted coordination for Eu . A careful crystallographic study was performed on the solid solutions of Cd Gd Eu O(BO ) (0≤x≤1) by Rietveld refinements. The as-doped Eu cations locate at the Gd site and are well separated by CdO , CdO and BO groups; thus, only a slight concentration quenching was observed at ≈80 atom % Eu . Most importantly, the parity-forbidden law of 4f-4f transitions for Eu are severely depressed, thus the absorptions at ≈393 and ≈465 nm are remarkable. Cd Gd Eu O(BO ) 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 R ≈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.