Dependence of Luminous Performance on Eu³⁺ Site Occupation in SrIn₂(P₂O₇)₂: The Effect of the Local Environment

Abstract

The photoluminescence behavior of luminescent materials with rare earth (RE) ions as a luminescence center not only depends on the element type and chemical valence of RE ions but also on their concentration and occupation in the matrix, sometimes including the interaction of the matrix and RE ions or between different RE ions. Herein, special SrIn₂(P₂O₇)₂ phosphate, assembled by monolayer [SrO₁₀]_∞ and bilayer [In₂P₄O₁₄]_∞ consisting of InO₆ units and P₂O₇ groups, was selected as the host material, and different cation positions (Sr and In) were substituted by Eu³⁺. The structure refinement in combination with Judd-Ofelt theory has shed light on the differences of the Eu³⁺ coordination environment in SrIn₂(P₂O₇)₂. The structural rigidity of the In³⁺ site is better than that of the Sr²⁺ site, making SrIn_1.92(P₂O₇)₂: Eu_0.08 superior in thermal stability. The average distance between adjacent Sr²⁺ ions is larger than that between adjacent In³⁺ ions, causing the higher quantum efficiency of Sr_0.9In₂(P₂O₇)₂: Eu_0.1. The present work demonstrates that the site occupation of Eu³⁺ has an important effect on its luminous performance. Importantly, the newly developed Eu³⁺-doped SrIn₂(P₂O₇)₂ phosphors, exhibiting outstanding luminous efficiency, favorable thermal stability, and excellent color purity, are promising red components of phosphor-based light-emitting diodes.