The electronic structure of alkaline-earth silicon nitride MSiN2 (M=Sr, Ba) was calculated using the CASTEP code. Both BaSiN2 and SrSiN2 are calculated to be intermediate band-gap semiconductors with a direct energy gap of about 2.9 eV for BaSiN2 and 3.0 for SrSiN2, as expected lower compared to the experimentally determined values (4.7 eV for BaSiN2 and 4.8 eV for SrSiN2 ) . The luminescence properties of Eu2+ and Ce3+ activated MSiN2 (M=Sr, Ba) have been studied. M1-xEuxSiN2 (0 x = 0.1): Eu2+ (M=Sr, Ba) can be efficiently excited in the UV to visible region (200 - 480 nm), making them attractive as conversion phosphors for LED applications. Ba1 xEuxSiN2 (0 x = 0.1) shows a broad emission band in the wavelength range of 500-750 nm with maxima from 602 to 628 nm with increasing the Eu concentration, while Sr1-xEuxSiN2 (0 x = 0.1) shows a broad emission band in the wavelength range of 550-850 nm with maxima from 670 to 685 nm with increasing the Eu concentration. Ce3+-doped MSiN2 (M=Sr, Ba) exhibits a broad emission band in the wavelength range of 400-700 nm with peak centre at 486 nm for BaSiN2 and 534 nm for SrSiN2. The long-wavelength excitation and emission of Eu2+ and Ce3+ ions in the host of MSiN2 (M= Sr, Ba) are attributed to the effect of a high covalency and a large crystal field splitting on the 5d bands of Eu2+ and Ce3+ in the nitrogen environment.
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