Synthesis And Optical Properties Of Cr³⁺ Ions In Gallate

In this paper, a series of red/near infrared Long-lasting phosphorescence Cr3+-dropedgallate was prepared by combustion method. The micro-structure of sample was characterizedby X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optical propertiesof the samples were characterized by excitation spectra, emission spectra, the decay curves ofthe afterglow, thermoluminescence (TL) curves.In order to improve the afterglow of the sample, we put in Ge(GeCl4) during preparationof Cr3+-droped gallate with spinel structure. After many experiments, we choose beterperformance material is ZnGe0.7GaO4-x:0.5%Cr3+. The results of XRD indicated that thesample has a good match with spinel structure. According to the ionic radius and coordination,It demonstrated that Cr3+and Ge4+had been incorporated into the lattice site of spinel.According to scanning electron micrographs of the sample, we observed its average diameteris about from a few hundred nanometers to a few microns.UV excitation, the emission spectra yield red emission, the peak is at694nm, which isdue to the2E-4A2transitions of Cr3+. The excitation peak at about584nm、440nm、320nm、270nm are attributed to the transitions of4A2-4T2,4A2-4T1(4F),4A2-2A1(2G),4A2-4T1(4P),respectively. These results suggest that Cr3+have been added to the spinel structure.After UV irradiation, the sample exhibits obvious afterglow emission. By analyzing theafterglow decay curve of the sample, we find that with the increase of vacuum treatmenttemperature, the sample of afterglow performance is enhanced.10h after irradiation we stillcan monitor to the afterglow. Afterglow of the best sample can achieve above20h. Theseresults suggest that vacuum heat treatment can produce more Zn vacancy, Ga vacancy, Gevacancy, O vacancy as traps.Thermoluminescence (TL) can study the influences of trap to afterglow. The results ofTL indicated that the sample have three trap levels. The more traps the sample have theperformance of afterglow is better. In order to further clarify the contribution of different trapsto the afterglow, samples of different time after irradiation has the thermoluminescence curves.It turned out that the afterglow mainly depends on the second trap.Our experimental results show that Cr3+doped gallate is a kind of better performance ofred/near infrared long persistence materials, has a great potential for development.