Roles of Nd3+ in enhancing Mn2+-Activated SrZn2(PO4)2 long persistent phosphor

Abstract

SrZn2(PO4)2: Mn2+, Nd3+ materials were synthesized using a solid-state reaction method. The prepared materials display long afterglow properties with a broadband yellowish-green emission at Peak 550 nm attributed to the 4T1 (4G) → 6A1 (6S) transition of the Mn2+ ion as a luminescent center. The sensitizing ion Nd3+ also contributes the green emission at the peak of 518 nm attributed to its 4G7/2 → 4I9/2 transition. The luminescent and structural properties of the materials were studied by XRD, SEM-EDS, XPS, excitation and emission spectra, decay curves and thermoluminescence (TL) and EPR analysis. The non-equivalent substitution of Nd3+ for Sr2+ results in NdSr• defects, which significantly increases the effective trap concentration of the materials. The fluorescence spectra show that there is a band overlap between the excitation spectrum of SrZn2(PO4)2: Mn2+ and the emission spectrum of SrZn2(PO4)2: Nd3+, illustrating a phenomenon of Nd3+ → Mn2+ energy transfer. The luminescent mechanism of the materials is explored.