Formation and photoluminescence of pure hexagonal and monoclinic Sm2+/Sm3+ codoped BaAl2Si2O8 phase using a simple sol–gel technique

The synthesis of pure hexagonal and monoclinic BaAl2Si2O8:Sm crystals using a simple sol–gel technique is discussed in detail. The pure hexagonal BaAl2Si2O8:Sm phase (H-BASO:Sm) can be obtained by adjusting the amount of the citric acid. The pure monoclinic BaAl2Si2O8:Sm phase (M-BASO:Sm) can be easily obtained by a three-step-calcinations process. Possibly it is the carbon existing in the crystal that can stabilize the hexagonal BaAl2Si2O8:Sm phase (H-BASO:Sm) and retard the conversion from the hexagonal to monoclinic phase. Photoluminescence, UV–vis absorption spectra and X-ray photoelectron spectra (XPS) demonstrate the existence of Sm2+ and Sm3+ ions in Sm doped H-BASO and M-BASO calcined under a reducing atmosphere. Photoluminescence properties of Sm3+ and Sm2+ ions in M-BASO and Sm2+ ions in H-BASO are reported.