Preparation, electronic structure and photoluminescence properties of RE (RE = Ce, Yb)-activated SrAISi4N7 phosphors

摘要

The electronic structure of SrAISi4N7 was calculated using the CASTEP code and SrAISi4N7 is an intermediate band gap semiconductor with an indirect energy gap of 3,6 eV. Ce~(3+) and Yb~(2+)-activated SrAISi4N7 samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. SrAISi4N7:Ce~(3+) shows a broad band emission in the wavelength range of 450-700 nm, originating from the 5d~1-4f~1 transition of Ce~(3+). The emission band of Ce~(3+) shifts to longer wavelength with an increase of Ce~(3+) concentration due to the increased Stokes shift and reabsorption by Ce~(3+). SrAISi4N7:Yb~(2+) can be excited efficiently over a broad spectral range between 300 and 550 nm, and exhibits a single intense red emission at 600 nm with a full width at half maximum of 95 nm due to the electronic transitions from the excited state of 4f~(13)5d to the ground state 4f14 of Yb~(2+). The low energy of Yb~(2+) emission in SrAISi4N7 can be attributed to the large nephelauxetic effect and crystal field splitting due to the coordination of Yb~(2+) by nitrogen. In addition, Sr_(1-2x)Ce_xLi_xAISi4N7 shows higher thermal stability in air than that of Sr_(1-y)Yb_yAISi4N7 (0≤,≤0.1).A white-light LED can be generated by using single SrAISi4N7:Ce~(3+) as the wavelength conversion phosphor combined with a blue LED chip (InGaN). The obtained LED exhibits a luminous efficiency of 74.3 Im W~(-1) at a corrected color temperature (CCT) up to 6350 K, and the color rendering index (CRI Ra) is around 78. These novel developed yellow-red phosphors have potential applications in spectral conversion materials for white-LEDs.