Fig. 1. Optical properties of CQD materials under increasing electric field in a capacitor device.

(A) Normalized PL and absorbance spectra of diluted CQDs in toluene. Left inset: Schematics of the core-shell-shell CQDs. Right inset: Transmission electron microscopy image of the CQDs indicating the shape distribution and the crystalline structure. Scale bar, 10 nm. (B) Schematics of the sandwich-like device structure. A sinusoidal-function bias (128 Hz) is applied to induce the electric field, and the device is optically pumped at a wavelength of 532 nm using a subnanosecond pulsed laser (500 ps/100 Hz). ITO, indium tin oxide. (C) Scanning electron microscopy image of a device’s cross section. Scale bar, 100 nm. (D) Electric field–dependent PL spectra of CdSe/CdS/ZnS CQDs with the pump fluence of 272 μJ/cm². These emission spectra exhibit intensity decease, redshift, and broadening with increasing electric field. a.u., arbitrary units. (E) Decrease in integrated PL intensity as a function of electric field, which was normalized by the zero-field integrated PL intensity. The solid line is a guide to the eye. It shows ~18% intensity drop in the maximum electric field of 264 kV/cm. (F) Electric field–dependent peak wavelength shift and PL spectrum broadening. The solid lines are guides to the eye. Only slight changes are observed here (~1.5-nm redshift and ~2-nm broadening under the maximum electric field).