White light emitting stannate pyrochlore based single phase phosphor CaLa1−xSnNbO7:xDy3+ for pc-WLED applications
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A new series of single phase pyrochlore based white phosphors, CaLa1−xSnNbO7:xDy3+ (x = 0.01, 0.02, 0.03, 0.04) and Ca1−ySryLa0.97SnNbO7:0.03Dy3+ (y = 0.1, 0.2, 0.3) were developed by a high temperature ceramic route. The phase purity and the crystalline structure of the as-prepared samples were characterised by powder X-ray diffraction method and the phosphors were found to crystallize into the cubic pyrochlore type structure. The photoluminescence properties were investigated and the results indicated that phosphors show a strong excitation levels in near UV (388 nm) and blue (452 nm) regions and emits intense complimentary blue (487 nm and 477 nm) and yellow (589 nm) light upon UV or blue excitation which can be assigned to the characteristic 4F9/2 → 6HJ (J = 13/2 and 15/2) transitions of Dy3+ respectively. Thus the suitable combination of the above complimentary colors, yellow and blue is an approach to realize a full color emission and the Commission Internationale de I’Eclairage (CIE) color coordinates of the resultant phosphors lie in the white light region (0.38, 0.36) close to the standard chromaticity coordinates (white light) of NTSC. The substitution of bigger ion like Sr2+ for Ca2+ enhanced significantly the photoluminescence properties by way of their excitation and emission intensities due to increased polarizability and distortion of the Dy3+ environment. These results demonstrate that CaLa1−xSnNbO7:xDy3+ and Ca1−ySryLaSnNbO7:0.03Dy3+ are promising single phased white phosphor for pc-WLED applications.
All the authors would like to acknowledge CSIR- National Institute for Interdisciplinary Science and Technology (NIIST), Thiruvananthapuram for providing the research facilities.
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