Investigation of thermal quenching of two emission centers in Sr9MnLi(PO4)7:Eu2+ using time-resolved technique
The thermal stability of phosphors in phosphor-converted light-emitting diodes (LEDs) plays an important role in the practical application of lighting. Herein, the Mn2+ based red-emitting phosphors of pure and Eu2+ doped Sr9MnLi(PO4)7 (SMPO) samples were prepared using the high temperature solid-state reaction method. The crystal field environment around Mn2+ ions was analyzed by combining the results of photoluminescence excitation spectrum and Tanabe-Sugano diagram. By comparing the results of X-ray photoelectron spectroscopy, two additional bands centered at 129.8 eV and 130.7 eV were found in Eu2+ doped sample, that corresponded to the chemical states of P 2p3/2 and P 2p1/2. Two different sets of emission spectra were observed in Sr9MnLi(PO4)7:5%Eu2+ (SMPO:Eu2+) employing the time-resolved technique. The emission peaks centered at 615 nm and 661 nm were attributed to Mn2+ and Eu2+ ions, respectively. The thermal quenching behaviors of Eu2+ and Mn2+ were investigated in the temperature range of 300-620 K, and the thermal quenching mechanisms were given in this work. The systematic research on luminescent properties of Eu2+ and Mn2+ ions in SMPO:Eu2+ phosphor contribute to providing an understanding of thermal stability, and conduce to the development of Mn2+ based red-emitting phosphors.