Terahertz-driven Luminescence and Colossal Stark Effect in CdSe:CdS Colloidal Quantum Dots

TL;DR

This study demonstrates that high-field terahertz pulses can induce colossal Stark shifts and luminescence in CdSe:CdS quantum dots, enabling extreme, rapid modulation of their electronic properties without material alteration.

Contribution

The paper introduces a novel method of using terahertz pulses to achieve ultrafast, large-scale bandgap modulation in quantum dots via the quantum confined Stark effect, surpassing previous electrostatic limitations.

Findings

Quantum dots exhibit luminescence driven by THz pulses without external charge.

Bandgap modulation exceeds 0.5 eV within picoseconds.

The observed effects are explained by the quantum confined Stark effect.

Abstract

Unique optical properties of colloidal semiconductor quantum dots (QDs), arising from quantum mechanical confinement of charge within these structures, present a versatile testbed for the study of how high electric fields affect the electronic structure of nanostructured solids. Earlier studies of quasi-DC electric field modulation of QD properties have been limited by the electrostatic breakdown processes under the high externally applied electric fields, which have restricted the range of modulation of QD properties. In contrast, in the present work we drive CdSe:CdS core:shell QD films with high-field THz-frequency electromagnetic pulses whose duration is only a few picoseconds. Surprisingly, in response to the THz excitation we observe QD luminescence even in the absence of an external charge source. Our experiments show that QD luminescence is associated with a remarkably high and rapid modulation of the QD band-gap, which is changing by more than 0.5 eV (corresponding to 25% of the unperturbed bandgap energy) within the picosecond timeframe of THz field profile. We show that these colossal energy shifts can be consistently explained by the quantum confined Stark effect. Our work demonstrates a route to extreme modulation of material properties without configurational changes in material sets or geometries. Additionally, we expect that this platform can be adapted to a novel compact THz detection scheme where conversion of THz fields (with meV-scale photon energies) to the visible/near-IR band (with eV-scale photon energies) can be achieved at room temperature with high bandwidth and sensitivity.