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 Ca_1.2Eu_0.8SiO₄.