Temporal evolution of white light emitting CdS core and Cd1-xZnxS graded shell quantum dots fabricated using single step non-injection technique

Abstract

White light emitting quantum dot (WQD) materials are being investigated due to their possible applications in the light emitting devices as single layer white light emitters and these have major advantage of lower re-absorption and self-absorption over multilayer emitters of different sized quantum dots (QDs). In this paper, white light emitting CdS core and Cd1-xZnxS graded shell based quantum dots have been synthesized using a single step non-injection technique. Detailed analysis of optical and structural properties has been carried out with QDs growth time. The photoluminescence (PL) consists a narrow band edge emission and a broad (in the range of 440–800 nm) trap state emission which results in white light emission and the quantum efficiency (QE) improves from ∼12% to 34% as growth time increases from 5 min to 30 min. The average fluorescence lifetime of band edge emission and trap state emission varies in the range of ∼2–5 ns and ∼250–550 ns respectively with QDs growth time. We have obtained a series of white light whose color coordinates are very close to the standard white light (CIE-1931); hence these QDs can be a good candidate for white light applications.