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A novel phosphate Ca9La(GeO4)0.75(PO4)6 was investigated to add to the family of phosphate phosphors and application in LEDs. In this work, the single phase red-emission Ce3+,Mn2+ co-doped phosphate Ca9La(GeO4)0.75(PO4)6 phosphor was synthesized by the solid-state reaction from both theoretical and practical points of view. The crystal structure was determined by Rietveld refinement and TEM. Its cell parameters are a = b = 10.4077605(2) Å, and c = 37.4714968(1) Å. The characteristic photoluminescence properties were studied in detail using photoluminescence excitation spectra, emission spectra, decay times and thermal quenching properties. Purple and red broad band emission from Ce3+ and Mn2+ was detected under excitation at 313 nm. According to this research, the Ca9La(GeO4)0.75(PO4)6:Ce3+,Mn2+ phosphor shows high thermal stability in the red-emission area. With the increase of the temperature, the intensity ratio of Mn2+ and Ce3+ emission rises rapidly and the purity of red-emission is improved. In order to reasonably explain this special phenomenon, an implicit mechanism between thermal quenching and energy transfer is proposed based on the configurational coordinate diagram. In addition, the mechanism could be helpful for understanding the thermal properties of multiple activators Ce3+ and Mn2+ co-doped phosphors as the reference. [ABSTRACT FROM AUTHOR]