Luminescence properties of a new green emitting long afterglow phosphor Ca14 Zn6Ga10O35:Mn2+,Ge4+

A series of green emitting persistent luminescence phosphors Ca14Zn6Ga10O35:Mn2+,Ge4+ have been synthesized via a solid state reaction method at 1230 degrees C. The X-ray diffraction spectra verified that all samples have a pure phase though the diffraction peaks exhibit a slight shift when the dopants added in. The green emission band peaking at 520 nm from Mn2+ was observed in the luminescence spectra of all the compounds with Mn2+ doping. The green afterglow can be perceived by naked eye in the dark environment for several minutes. With the Ge4+ co-doped, the quadrivalent Mn4+ existing in the Mn singly doped sample can be more sufficiently reduced to Mn2+ as indicated by the substantially subdued red emission from Mn4+ in the co-doped samples. From the photoluminescence spectra, 0.3% Mn2+ was determined to be the optimal Mn concentration for strongest emission. The decay curves of the Mn2+ emission from samples with different doping concentration were also recorded. It is found that the 0.5% Mn2+ sample yields the best afterglow performance in accordance with its stronger thermoluminescence intensity. The similar thermoluminescence curves of all samples suggests the similar distribution of traps occurring in the same host. Based on the experimental results, a model is proposed to discuss the persistent luminescence processes of the samples.