Photoluminescence properties of near ultraviolet excited Ca₈La₂(PO₄)₆O₂:Sm³⁺ red orange phosphor

Abstract

Novel Ca₈La₂(PO₄)₆O₂:Sm³⁺ phosphors are successfully synthesized in air by the high temperature solid state reaction method. The X-ray diffraction patterns, morphology, energy spectrum diagram, elemental mapping, luminescence properties, concentration-dependent emission spectra, thermal stability, and decay curves are investigated. The excitation spectrum of Ca₈La₂(PO₄)₆O₂:8%Sm³⁺ phosphor monitored at 604 nm extends the region from 220 nm to 520 nm with many excitation spectral bands because of the O²⁻–Sm³⁺ charge transfer band and the f–f transitions of Sm³⁺ ion. Ca₈La₂(PO₄)₆O₂:Sm³⁺ phosphor with excitation at 402 nm emits red orange light in the range of 550–770 nm with many emission spectral bands derived from the ⁴G_5/2 → ⁶H_5/2 (550–570 nm), ⁴G_5/2 → ⁶H_7/2 (570–630 nm), ⁴G_5/2 → ⁶H_9/2 (630–690 nm), and ⁴G_5/2 → ⁶H_11/2 (690–760 nm) transitions of Sm³⁺ ion, and the optimal Sm³⁺ concentration is ~ 8 mol%. The lifetime of Ca₈La₂(PO₄)₆O₂:Sm³⁺ phosphor decreases from 1.39 to 1.11 ms with increasing Sm³⁺ concentration from 2 to 12 mol%. Ca₈La₂(PO₄)₆O₂:Sm³⁺ phosphor has the good thermal stability and emission color stability. The luminous mechanism, concentration quenching, and thermal quenching are explained, respectively. The experimental results indicate that Ca₈La₂(PO₄)₆O₂:Sm³⁺ phosphor as red orange component has a potential application in white LED based on near ultraviolet LED chip.