Considerable improvement of Na2CaSn2Ge3O12:Eu3+ reddish orange long-persistent phosphorescence with Co-doping of Dy3+

A novel reddish orange long persistent phosphorescence was observed in Na2CaSn2Ge3O12:Eu3+ and Na2CaSn2Ge3O12:Eu3+,Dy3+ phosphors which were prepared using conventional solid-state method at 1250 degrees C in air. X-ray diffraction analyses demonstrate that all samples consist of Na2CaSn2Ge3O12 as the predominant phase. With the excitation of 318 nm, all the samples can emit reddish orange light, which is attributed to the D-5(0)-> F-7(1) transition of Eu3+. The Dy3+ as co-dopants greatly prolong the phosphorescent persistence time of Na2CaSn2Ge3O12:Eu3+ phosphor. The persistent time of the persistence is 5 h, remarkable increased by 21-fold after the co-doping of 0.4 mol% Dy3+. The significant changes in the thermoluminescence curves demonstrated that the incorporation of Dy3+ into Na2CaSn2Ge3O12:Eu3+ not only enriched the types of traps, but also greatly increased the concentration of original traps (V'(Ca),V ''(Na). It can be seen from the photoluminescence, long persistent phosphorescence and thermoluminescence spectra of all obtained samples that the optimal composition is Na2CaSn2Ge3O12:1.2%Eu3+,0.4%Dy3+. The possible mechanism of the reddish orange long persistent phosphorescence phosphor Na2CaSn2Ge3O12:Eu3+,Dy3+ is investigated.