Blue emitting thin-film electroluminescent devices utilizing Tm-doped ZnS nanocrystals

Novel blue thin-film electroluminescent (TFEL) devices comprised of Tm 3+ -doped ZnS nanocrystals (NCs) have been investigated employing a conventional double insulating TFEL device structure. The luminescent properties of Tm 3+ -doped ZnS NCs (ZnS:Tm) with different Tm concentrations are studied in comparison with those of the ZnS:Tm thin film and phosphor. The concentration quenching effects of both photoluminescence (PL) and electroluminescence (EL) were observed when the Tm concentration was in excess of 3 mol%. In contrast with the EL spectrum of conventional ZnS:Tm TFEL device, in which infrared emission band is dominant rather than blue emission band, the blue emission band prevails in the EL spectrum of the ZnS:Tm NC TFEL device. Furthermore, as the driving-voltage increased, the EL intensity of the blue band relatively increased in comparison with the increase in the EL intensity, which indicates the EL excitation mechanism is ascribed to direct-impact excitation of Tm 3+ by hot-electrons. Finally, the full-color TFEL device utilizing the activator-ion-doped ZnS NCs is demonstrated, and the operation characteristics of the full-color TFEL device are presented.