Multicolored Cd1−xZnxSe quantum dots with type-I core/shell structure: single-step synthesis and their use as light emitting diodes

Abstract

We developed a single-step hot-injection process to synthesize Cd_1−xZn_xSe quantum dots (QDs) with tunable emission wavelengths. The multiple emission colors of the Cd_1−xZn_xSe QDs resulted from the variation in their compositions (x value) with the reaction time. Because of the higher reactivity of the Cd precursor, QDs whose composition was rich in CdSe were generated at the beginning of the reaction. As the reaction proceeded, the later-formed ZnSe shell was simultaneously alloyed with the core, giving rise to a progressive alloying treatment for the grown QDs. During the reaction period, the emission color of the Cd_1−xZn_xSe QDs shifted from red to orange, to yellow, to green and finally to blue. A light emitting diode (LED) composed of multilayers of ITO/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate)/poly(3-hexylthiophene) blended with Cd_1−xZn_xSe QDs/Al was fabricated to test the electroluminescence (EL) properties of the QDs. The EL results show high color purity for the emission from LED devices containing Cd_1−xZn_xSe QDs, revealing that the as-synthesized QDs can be easily processed and integrated into a light-emitting device without using a complicated procedure. The findings from the present work also demonstrate the advantage of using the current single-step synthetic approach to obtain a batch of Cd_1−xZn_xSe QDs that may emit different colors in prototype LEDs.