Effect of local structure of Sm3+ in MgA12O4:Sm3+ phosphors prepared by thermal decomposition of triethanolamine complexes on their luminescence property

Samarium doped magnesium aluminate phosphors were successfully synthesized from a facile metaltriethanolamine complex method. The powders were obtained from calcining the metal complexes at various temperatures (800-1200 degrees C). Functional groups of the complexes and the calcined powders were determined by FT-IR. According to XRD patterns, no crystalline impurities were observed in the synthetic products. Morphology of the calcined products was studied by FE-SEM and TEM. The SEM and TEM results showed that the raising of calcination temperature enlarged the particle sizes of samarium doped magnesium aluminate due to particle agglomeration at high temperature. The prepared phosphors showed the characteristic photoemission peaks at 565, 602, 648 and 738 nm. XANES study revealed that the samarium dopant was in the valency state of 3+. Therefore, the luminescent peaks can be identified as the electronic transitions from the excited state 4(5/2)(G) to H-6(11/2), H-6(9/2), H-6(7/2), H-6(5/2) levels, respectively. Interestingly, the calcination at 800 degrees C leaded to the most intense luminescence signal. From the EXAFS analysis, the local structure of Sm3+ from the sample obtained at 800 degrees C was not crystalline as only the first coordination shell was observed. The local structure of Sm3+ for samples calcined at other temperatures showed higher coordination shells. It can be concluded from the present work that Sm3+ in the environment of low periodicity exhibited a stronger luminescence. Furthermore, it was found that the optimum Sm3+ content for this series of phosphors was 1%. (C) 2017 Elsevier B.V. All rights reserved.