Red Emitting Ca2SiO4:Eu2+ Phosphors for White Light Emitting Diodes

Development of highly efficient red phosphors available in the excitation by UV-and/or blue-LEDs is one of the most important issues to improve the performance of white-LEDs because the color rendering index of most commercial white-LEDs which consisted of blue-LEDs and YAG:Ce3+ is relatively low owing to a lack of red-light region. 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. Alkaline earth orthosilicate phosphors activated with Eu2+ 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 silicon-based oxide phosphors are advantageous for the commercial production of red phosphors. We have already reported red-emitting CaSrSiO4:Eu2+ phosphors excited by blue-light region.1) The wavelength at the maximum emission of CaSrSiO4:Eu2+ with Eu2+ of 10 mol.% was 615nm. In addition, we have recently discovered new red-emitting Ca2SiO4:Eu2+ phosphors with higher Eu2+ concentrations at 20-40 mol.% excited by blue-light region.2) Although Ca2SiO4:Eu2+ phosphors with Eu2+ of 0.1–5.0 mol.% exhibited a strong green emission excited under UV light region,3) Ca2SiO4:Eu2+ with Eu2+ of 20–40 mol.% exhibited red emission peaking at 640–655 nm when excited at 450 nm and the emission intensity was 1.05 times higher than that of commercial YAG:Ce3+ (P46). The new red-emitting Ca2SiO4:Eu2+phosphors should be one of the promising candidates for the next-generated red phosphors in the white LED applications. Reference: 1) S. Tezuka, Y. Sato, T. Komukai, Y. Takatsuka, H. Kato and M. Kakihana, Appl. Phys. Express 6 (2013) 072101, 2) Y. Sato, H. Kato, M. Kobayashi, T. Masaki, D. H. Yoon and M. Kakihana, Angew. Chem. Int. Ed. 53 (2014) 7756, 3) Y. Y. Luo, D. S. Jo, K. Senthil, S. Tezuka, M. Kakihana, K. Toda, T. Masaki, D. H. Yoon, J. Solid State Chem. 189(2012) 68. Figure: Fig. 1 Emission and excitation spectra of Ca1.2Eu0.8SiO4. Figure 1