Photoluminescence Properties of Red-Emitting Ca3ZrSi2O9:Eu2+ Phosphors

It has been well-known that silicon-based nitride phosphors such as CaAlSiN3:Eu2+ and Sr2Si5N8:Eu2+ possess excellent red-light emission when excited by blue-light region. However, preparation of such silicon-based nitride phosphors in pure form should be needed to sinter precursor powders under high pressure and temperature conditions. On the contrary, Eu2+-activated silicates with alkaline earth ions have been reported as high efficient phosphors. Such silicon-based oxide phosphors in pure form can be easily obtained by simple preparation techniques without any critical conditions mentioned above. Therefore, productivity and production cost for silicate phosphors are advantageous for the commercial production of red phosphors. We have reported red-emitting Ca1.2Eu0.8SiO4 phosphors excited by blue light region.1) The wavelength at the maximum emission of Ca1.2Eu0.8SiO4 phosphors was 650nm.1) We have recently discovered new red-emitting Ca3ZrSi2O9:Eu2+ phosphors with high Eu2+ concentration excited by near-UV and blue-light region. Ca3ZrSi2O9 activated by low Eu2+ concentrations (Eu2+: 1 mol%) exhibited a green emission at 530 nm. However, with increasing Eu2+ concentration to 10 mol%, Ca3ZrSi2O9:Eu2+ phosphors exhibited red emission peaking at 650 nm while the green emission disappeared. Based on the crystal structure data of Ca3ZrSi2O9, there were three Ca sites in Ca3ZrSi2O9, where Eu2+ ions were occupied.2) Two of the Ca sites were smaller than another Ca site. We presume that emission at 530 nm from Eu2+ occupying the large Ca site was not observed owing to Eu2+ concentration quenching, as well as reabsorption of the green emission light from Eu2+ at the large Ca site by Eu2+ at the two small Ca sites. Thus, the deep-red emission of Ca3ZrSi2O9:Eu2+ phosphors observed is considered to be emission from Eu2+occupying these small Ca sites. 1) Y. Sato, H. Kato M. Kobayashi, T Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed. 53(2014) 7756. 2) J. R. Plaister, J. Jansen, R. G. de Graaff, D. J. W. IJdo, J. Solid State Chem. 115 (1995) 464.