Intense NUV excitation of Eu3+ in LiSrY2(BO3)3 by utilizing the local symmetry-broken characteristic: A candidate for NUV LED pumped red phosphor

Abstract

Eu3+-based phosphors usually possess a very strong O2--Eu3+ charge transfer absorption, while the f-f absorptions in the NUV range are suppressed due to the parity-forbidden law. Once Eu3+ locates in a noncentrosymmetric coordination, the f-f absorptions are supposed to be enhanced, thus it possibly behaves as the NUV LED pumped red phosphor. In LiSrY2(BO3)3, Y3+ locates on the mirror plane in the average structure, but the local symmetry of the surrounding environment is in fact reduced from Cs to C1 due to the half-occupancy of O4. In this contribution, complete solid solutions of LiSr(Y1-xEux)2(BO3)3 were prepared by high temperature solid state reactions. The phase purity was confirmed by powder X-ray diffraction, moreover, the Eu3+-to-Y3+ substitutions were proved to be successful by the close-to-linear expansion of the unit cell volume. Indeed, Eu3+ in LiSrY2(BO3)3 possesses very intense f-f absorptions with the strongest one at 394 ​nm. A slight concentration quenching was observed at x ​= ​0.7, and the representative phosphor LiSr(Y0.3Eu0.7)2(BO3)3 emits a bright red light under either a 365 ​nm UV lamp or excited by the 390–395 ​nm LED chip. The structure-property relationship in this work provides an interesting strategy to develop NUV LED pumped red phosphors.