AbstractsEarth & Environmental Science

Characterization and Optical Properties of Nanocrystalline Alkaline Earth Halides of the Formula MFX:RE2+/3+ (M= Ba, Sr, Ca; X= Cl, Br, I; RE= Sm, Eu) Prepared by Co-Precipitation and Ball-Milling

by Xianglei Wang

Institution: University of New South Wales
Department: Physical, Environmental & Mathematical Sciences
Year: 2014
Keywords: rare earth ions doped; X-ray storage phosphors; nanocrystalline alkaline earth fluorohalides; room temperature; mechanochemical synthesis; solid solutions
Record ID: 1051554
Full text PDF: http://handle.unsw.edu.au/1959.4/53973


Nanocrystalline alkaline earth fluorohalides MFX (M= Ba, Sr, Ca; X= Cl, Br, I) doped with divalent and trivalent rare earth metal ions (RE= Eu, Sm) were prepared at room temperature by either co-precipitation of aqueous solutions or ball-milling of solid solutions. These as-prepared products were characterized and investigated by a variety of physical and spectroscopic techniques. The room temperature co-precipitation method was employed to prepare nanocrystalline BaFCl:Eu2+ by the reduction of Eu3+ to Eu2+ using granular Zn in solution under a nitrogen atmosphere. The divalent oxidation state of europium ions in the as-prepared sample was confirmed by photoluminescence and cathodoluminescence characterization, and the temperature dependence of observed Eu2+ transitions was investigated via a high resolution photoluminescence measurement. Moreover, nanocrystalline BaFCl:Sm3+ was also prepared, by a controlled co-precipitation method in methanol/water solutions, and it was found that the ratio of methanol/water in solution had an impact on the growth of crystals. The room temperature mechanochemical synthesis of BaFCl:RE2+ (RE= Sm, Eu) by ball-milling under a nitrogen atmosphere was shown to be a very efficient method for the preparation of optical materials doped with rare earth ions in the unstable divalent oxidation. In particular, the as-prepared nanocrystalline BaFCl:Sm2+ was characterized via a series of spectroscopy experiments, and the ratio of Sm2+/Sm3+ ions was estimated to confirm the predominance of the divalent oxidation state in the sample. Furthermore, the influence of ball-milling time on the as-prepared nanocrystalline BaFCl:Eu2+ was also investigated by photoluminescence measurements. The room temperature ball-milling method was also employed to prepare complex MFX:Sm3+ (M= Ba, Sr, Ca; X= Cl, Br, I) compounds in air. Some of the factors in the ball-milling process which affected the final products were investigated by powder X-ray diffraction and photoluminescence measurements. The performance of the ball-milled products was examined by the evaluation of X-ray dose dependence and spectral hole-burning properties of alloyed nanocrystalline Ba0.5Sr0.5FCl0.5Br0.5:Sm3+.