Spherical organic-bonded ZnS nanocrystals with 4.0±0.2 nm in diameter are synthesized by a liquid-solid-solution method. The photoluminescence spectrum of sample ([S 2− ]/[Zn 2+ ] = 1.0) shows a strong white emission with a peak at 490 nm and ∼ 170 nm full widths at half maximum. By Gauss fitting, the white emission is attributed to the overlap of a blue emission and a green-yellow emission, originating from electronic transitions from internal S 2− vacancies level to valence band and to the internal Zn 2+ vacancy level, respectively. After sealingZnS nanocrystals onto InGaN chips, the device shows CIE coordinates of (0.29,0.30), which indicates their potential applications for white light emitting diodes.
High-quality water-soluble ZnS:Pb2+ nanocrystals were synthesized via a simple chemical codepositing method. The as-synthesized ZnS:Pb2+ nanocrystals show high monodispersity and crystallinity with a narrow size distribution (3.2 +/- 0.4 nm). ZnS:Pb2+/ZnS core/shell structures were also obtained by coating a ZnS shell displaying significantly enhanced photoluminescence (PL) intensity and photostability. For the ZnS:Pb2+/ZnS samples the position of emission spectrum shows a red-shift of approximately 10 nm, which produces a fairly pure white emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.31, 0.33). These phenomena are explained by a model of multiple Pb2+ luminescent centers.
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