Improved preparation technology of color-tunable long afterglow phosphors Sr1.94-xCaxMgSi2O7: Eu2+0.01, Dy3+0.05

Tetragonal long afterglow silicates, Sr1.94-xCaxMgSi2O7: Eu2+0.01, Dy3+0.05 (x=0, 0.388, 0.776, 1.164, 1.552, 1.94), are successfully synthesized by high-temperature solid-state reaction at 1300 °C and 1350 °C, respectively. Addition of excess silicon dioxide can reduce the sintering temperature from 1350 °C to 1300 °C, and photoluminescence performances and afterglow properties are improved. All samples have the same tetragonal structure, but the diffraction peaks shift to higher angles when smaller Ca2+ ions gradually substitute Sr2+ sites in the host. The reduced interplanar spacing leads to increscent crystal field strength. As a result, a red shift phenomenon is observed in the emission spectra with the increase of Ca2+ content. The afterglow emission bands also change from 466 to 529 nm when the proportion of Ca2+ ions increases in the host. Both luminescence and afterglow colors can continuously vary from blue to green by adjusting the Ca/Sr ratio in the host, and emission wavelength is linear with the concentration of Ca2+(x). With increasing the concentration of Ca2+, the thermal stability is improved and the quenching temperature increases, but the afterglow properties deteriorate.