Design, synthesis, crystal structure and luminescent properties introduced by Eu3+ of a new type of rare-earth borophosphate CsNa2REE2(BO3)(PO4)2 (REE = Y, Gd)

Abstract

The rich compositional and structural diversity of borophosphates provides a wide variety of host lattices for luminescent materials. Herein, we report a borophosphate, CsNa₂REE₂(BO₃)(PO₄)₂ (REE = Y, Gd), with a new type of three-dimensional (3D) anionic framework of [REE₂(BO₃)(PO₄)₂]_∞. In this structure, REE³⁺ ions are in a linear array and the nearest intraline REE–REE distance is above 6.9 Å. Surprisingly, the Eu³⁺ activated phosphors CsNa₂REE_2(1−x)Eu_2x(BO₃)(PO₄)₂ show an insignificant concentration quenching effect; the higher the Eu³⁺ concentration, the larger the absolute luminescent external quantum yield. The 100% Eu³⁺ phosphor CsNa₂Eu₂(BO₃)(PO₄)₂ possesses an IQY of 59% under 394 nm excitation. Moreover, CsNa₂Eu₂(BO₃)(PO₄)₂ phosphor possesses superior thermal stability in the range 30–200 °C, retaining more than 96% of its initial intensity at 200 °C. We believe the prepared phosphor has potential application as a red phosphor for NUV excited LEDs.