Synthesis and luminescent characteristics of Sr₂ Ga₂S₅:Eu²⁺ yellow phosphor for LEDs

Nowadays, LEDs has been applied to the luminescent devices of various fields because of the invention of high efficient blue chip. Recently, especially, the white LEDs composed of InGaN blue chips and a yellow phosphor (YAG:Ce³⁺) have been investigated extensively. With the exception of YAG:Ce³⁺ phosphor, however, there are no reports on yellow phosphor that has significant emission in the 450-470 nm excitation range and this LED system is the rather low color rendering index due to their using two wavelength. Hence, we have attempted to synthesize thiogallate phosphors that efficiently under the long wavelength excitation range in the present case. Among those phosphors, we have synthesized Sr₂Ga₂S₅: Eu²⁺ phosphor by change the host material of SrGa₂ S₄:Eu²⁺ which is well known phosphor and we investigated the luminescent properties. In order to obtain the harmlessness and simplification of the synthesis process, sulfide materials and mixture gas of 5 % H₂/95 % N₂ were used instead of the CS₂ or H₂S gas. The prepared phosphor shows the yellow color peaking at the 550 nm wavelength and it possible to emit efficiently under the broad excitation band in the range of 300-500 run. And this phosphor shows high luminescent intensity more than 110 % in comparison with commercial YAG:Ce³⁺ phosphor and it can be applied for UV LED due to excitation property in UV region.