Crystal structure and luminescence dynamics of highly pure LiM(PO3)3:Eu3+ (M = Sr, Ca) red phosphors for white light emitting diodes

Abstract

Highly pure red phosphors LiM(PO₃)₃:Eu³⁺ (M = Sr, Ca) doped with Eu³⁺ (1 mol%) were synthesized via solution combustion method and their crystal structure and luminescence dynamics were studied to explore its suitability in white light emitting diodes. The Rietveld refinement analysis of the powder X-ray diffraction patterns reveals that the phosphors belong to the pure triclinic phase of LiSr(PO₃)₃ and LiCa(PO₃) with space group P-$\overline{1}$ (2). The scanning electron microscopy images showed the agglomerated morphology. The photoluminescence emission spectra under 393 nm show an orange band at 594 nm and a red band at 613 nm ascribed to ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂ transitions of Eu³⁺ ion in both the phosphors. Moreover, the spectroscopic properties such as luminescence behaviour, and Stark splitting were used to examine the symmetry of Eu³⁺ ions in LiM(PO₃)₃:Eu³⁺ (M = Sr, Ca) phosphors in terms of distortion induced upon doping. The Stark splitting shows that the actual site symmetry for Eu³⁺ ion was estimated to be D₂ type for both phosphors. The photometric properties of LiCa(PO₃)₃:Eu³⁺ such as Commission International de l’Eclairage coordinates (x = 0.64, y = 0.36) near to the standard one (red), high color purity (95%) and higher brightness reveal that the phosphor has the capability of acting as a red component in n-UV white light emitting diodes.