Terahertz-Driven Luminescence and Colossal Stark Effect in CdSe–CdS Colloidal Quantum Dots

Abstract

Optical properties of colloidal semiconductor quantum dots (QDs), arising from quantum mechanical confinement of charge, present a versatile testbed for the study of how high electric fields affect the electronic structure of nanostructured solids. Studies of quasi-DC electric field modulation of QD properties have been limited by electrostatic breakdown processes under high externally applied electric fields, which have restricted the range of modulation of QD properties. In contrast, here 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 bandgap, which changes by more than 0.5 eV (corresponding to 25% of the unperturbed bandgap energy). We show that these colossal energy shifts can be explained by the quantum confined Stark effect even though we are far outside the regime of small field-induced shifts in electronic energy levels. Our results demonstrate a route to extreme modulation of material properties and to a compact, high-bandwidth THz detector that operates at room temperature.

Two-Dimensional Spectroscopy at Terahertz Frequencies

“…It is time-delayed relative to and spatially overlapped at the sample with the THz pump pulse(s). The optical responses of the sample induced by the THz field, such as absorption [51], frequency shifts [52], optical harmonic generation [53], birefringence [54], and polarization rotation [55], are detected. Examples of THz pump-optical birefringence probe spectroscopy include the THz Kerr effect in liquid molecules [37,54,56], and ferroelectric crystals [57,58], and THz-induced dipolar alignment of polar gas molecules [59,60].…”

Terahertz and infrared nonlocality and field saturation in extreme-scale nanoslits

“…Extending such investigations to longer wavelength regimes, in particular, millimeter-wave or terahertz (THz) and infrared (MIR) regime (wavelengths 0.75-20 µm), is important for two reasons. First, researchers have demonstrated substantial field enhancements in metal-insulator-metal (MIM) structures that are resonant in the MIR [20,33] and THz regimes [34][35][36][37][38][39]. Naturally, one could ask how the nonlocal effect limits field confinement and enhancement in such cases.…”

Confined Growth of Quantum Dots in Silica Spheres by Ion Exchange of “Trapped NH4+” for White-Light Emission

“…Quantum dots (QDs) have remained a hot spot of research in the past few decades because of their fascinating optical and electronic properties. Among many applications, [1][2][3][4][5][6][7][8][9][10][11][12] QD-based white-light-emitting diodes (QD-WLEDs) have attracted wide attention because of their excellent optical properties as well as good thermal and chemical stability. 13 Conventionally, fabrication of QD-WLEDs requires discrete color mixing or color conversion techniques and involves complex processes, such as optical blending of several colors of electroluminescent emissions.…”