Controllable two-dimensional luminescence tuning in Eu2+,Mn2+ doped (Ca,Sr)9Sc(PO4)7 based on crystal field regulation and energy transfer

Abstract

Currently, controllable luminescence tuning and the generation of single component white emission are viable strategies to modify and optimize the luminescence performances of phosphors, which offer appealing prospects for the w-LED lighting industry. In this paper, we designed two-dimensional (2D) tunable color coordinates on the CIE diagram in the Eu²⁺,Mn²⁺ doped (Ca,Sr)_9xSc(PO₄)₇ system by a combination of crystal field regulation and the energy transfer method. X-ray powder diffraction (XRD) and Rietveld refinement were utilized to analyze the phase composition and structural variation of the studied phosphors. The transmission electron microscopy (TEM) and photoluminescence spectra were exploited to analyze the generation of nanosegregation. The effects of the schedule of cation substitutions and energy transfer on the photoluminescence properties were investigated in detail. The corresponding luminescence mechanisms of the red-shifted emission with Sr²⁺ → Ca²⁺ substitution and Eu²⁺ → Mn²⁺ energy transfer were deeply discussed and proposed. In addition, the temperature-dependent thermal quenching behavior and the electroluminescence (EL) performance of the fabricated w-LED devices were also investigated to characterize the prepared Ca_{9(1−0.03−x−y)}Sr_9xSc(PO₄)₇:0.27Eu²⁺,9yMn²⁺. Finally, a representative w-LED device composed of a 369 nm UV chip and Ca_{9(1−0.03−0.02−0.5)}Sr_4.5Sc(PO₄)₇:0.27Eu²⁺,0.18Mn²⁺ could present excellent EL performance with the parameters CRI = 88, CCT = 3122 K and color coordinate (0.45, 0.44), which could well meet the commercial standard of warm white light. Therefore, our results suggest that this two-step luminescence tuning method is feasible to be applied in other phosphor systems for obtaining efficient white emitting phosphors.