Continuously voltage-tunable electroluminescence from a monolayer of ZnS quantum dots

A monolayer electroluminescence (EL) device with ZnS quantum dots (QDs) as emitting layer was fabricated by spin-coating technique. Continuously tunable EL spectra from ZnS QDs are observed at room temperature. By increasing excitation voltage, the EL spectra can be tuned from yellow green (560 nm) to blue (470 nm), corresponding to chromaticity coordinates from (0.45, 0.52) to (0.22, 0.26). In order to understand the mechanism of the device, the dependences of the photoluminescence of the ZnS QDs on temperature, excitation energy, and particle size have been studied, respectively, which indicates that the possible mechanisms of tunable EL spectra are related to selective excitation of QDs with different particle sizes.