Novel white-emitting afterglow phosphor Na2CaSn2Ge3O12:Dy3+: Preparation, photoluminescence, and phosphorescence properties

Afterglow was found in germanate (Na2CaSn2Ge3O12) doped with Dy3+ phosphor, which was prepared at 1250 °C through the traditional solid-state reaction in air. Na2CaSn2Ge3O12:Dy3+ phosphors were comprehensively characterized by XRD, photoluminescence excitation and emission spectra, thermo-luminescence and long persistent phosphorescence decay curves to study the effects of the Dy3+ concentration on their properties. The XRD results indicates that a single phase of Na2CaSn2Ge3O12 can be obtained. Upon excitation by 248-nm UV light, all samples emit white light, which is composed of yellow and blue originating from the Dy3+ (4F9/2→6HH/2, H = 11, 13, 15 transition). The Na2CaSn2Ge3O12:Dy3+ phosphor exhibited the perfect luminescent property and longest afterglow time when the Dy3+ concentration was 0.6 mol%. The CIE chromaticity coordinates for Na2CaSn2Ge3O12:Dy3+ were (0.3916, 0.3914). From the long persistent phosphorescence decay curve of the Na2CaSn2Ge3O12:Dy3+ phosphor, it was concluded that this process contains a fast and a slow decay. The afterglow luminescence from the Na2CaSn2Ge3O12:Dy3+ phosphor persisted for more than 7.8 h after irradiation with ultraviolet lamp. The Na2CaSn2Ge3O12:Dy3+ phosphor is deemed to be a potential storage phosphor that can be applied in the field of practical application. After incorporation of Dy3+ into the Na2CaSn2Ge3O12 matrix, new foreign traps (DyCa°, DyNa°°) were produced, and the concentration of internal traps (VCa″, VNa′) increased approximately 10 times. The luminous mechanism of the Na2CaSn2Ge3O12:Dy3+ phosphor was studied.