Chameleon-like photoluminescence of (Sr,Mg)2Si(O,N)4:Eu2+ nitridosilicate phosphors

Sr2-xMgxSi(O,N)4:Eu2+ nitridosilicate powders were synthesized using a high-temperature nitridation process. X-ray diffraction data and photoluminescence (PL) spectra demonstrated that the Mg2+ ions were incorporated into the Sr2+ sites rather than the interstitial sites. The Mg2+ substitution led to a phase transformation and affected the PL properties. There were two Eu2+ sites: Eu(I) and Eu(II). The PL spectra of the Sr2SiO4:Eu2+ powders consisted of two emission bands (A- and B′-bands) in the blue and green regions assigned to Eu(I) and Eu(II), respectively. Remarkably, the Sr2-xMgxSi(O,N)4:Eu2+ powders exhibited an additional emission band (B-band) in the red region, which originated from the large red-shift of the B′-band due to the coexistence of the Eu‒O and Eu‒N bonds. Furthermore, the PL spectra were hypersensitive to the excitation wavelength, resulting in chameleon-like luminescence properties. The PL properties were explained using a structural analysis, multiple Gaussian fit of the spectra, and thermal quenching.