Temperature-dependent emission spectra of M2SiO4:Eu2+ (M=Ca, Sr, Ba) phosphors for green and greenish white LEDs

The temperature dependence of emission spectra of alkaline earth ortho-silicates M2SiO4 (M=Ca, Sr, Ba) doped with Eu2+ ions is investigated. Two emission bands of Sr2SiO4:Eu2+ show the normal redshift with broadening bandwidth and decreasing emission intensity as an increase in temperature. On the other hand, emission bands of Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+ show the anomalous blueshift with increasing temperature. For Ca2SiO4:Eu2+ and Ba2SiO4:Eu2+, the temperature dependence of the emission color can be described in terms of back tunneling from the excited state of low-energy emission band to the excited state of high-energy emission band in the configuration coordinate diagram. Our phosphors have a promising potential as phosphors for green or greenish white-light-emitting diode pumped by ultraviolet chip.