Temperature-dependent optoelectronic properties of quasi-2D colloidal cadmium selenide nanoplatelets

Abstract

Colloidal cadmium selenide (CdSe) nanoplatelets (NPLs) are a recently developed class of efficient luminescent nanomaterials suitable for optoelectronic device applications. A change in temperature greatly affects their electronic bandstructure and luminescence properties. It is important to understand how and why the characteristics of NPLs are influenced, particularly at elevated temperatures, where both reversible and irreversible quenching processes come into the picture. Here we present a study of the effect of elevated temperatures on the characteristics of colloidal CdSe NPLs. We used an effective-mass envelope function theory based 8-band k·p model and density-matrix theory considering exciton-phonon interaction. We observed the photoluminescence (PL) spectra at various temperatures for their photon emission energy, PL linewidth and intensity by considering the exciton-phonon interaction with both acoustic and optical phonons using Bose-Einstein statistical factors. With a rise in temperature we observed a fall in the transition energy (emission redshift), matrix element, Fermi factor and quasi Fermi separation, with a reduction in intraband state gaps and increased interband coupling. Also, there was a fall in the PL intensity, along with spectral broadening due to an intraband scattering effect. The predicted transition energy values and simulated PL spectra at varying temperatures exhibit appreciable consistency with the experimental results. Our findings have important implications for the application of NPLs in optoelectronic devices, such as NPL lasers and LEDs, operating much above room temperature.

Strong Plasmon-Wannier Mott Exciton Interaction with High Aspect Ratio Colloidal Quantum Wells

“…To further confirm our interpretation, we computed the exciton binding energy in 4 ML CdSe CQWs with varying lateral sizes (the energy of free electron-hole pairs were calculated by means of the 8-band k, p model; then, using the measured first excitonic absorption features, the exciton binding energy can be extracted; see details in Note S3). 51 Figure 3B shows that the exciton binding energy holds a negative correlation with the lateral size of the CQWs, in agreement with our previous explanation. Notably, when the lateral size is close to or beyond the Bohr radius (vertical dashed line in Figure 3B), E bx is enhanced by more than 50% compared with the value in square-shaped CQWs.…”

“…Notably, when the lateral size is close to or beyond the Bohr radius (vertical dashed line in Figure 3B), E bx is enhanced by more than 50% compared with the value in square-shaped CQWs. 38,51 Fast exciton consumption is another challenge in hybrid systems because energy exchange needs to be faster than any dissipative processes in excitons to achieve a strong interaction. 1 Self-assembling (or stacking) in CQW solid film has been problematic for exciton reservation.…”

All-optical control of exciton flow in a colloidal quantum well complex

“…On the other hand, stimulated emission, in which the exciton recombination dynamics dramatically differs from that in spontaneous emission, is a possible control mechanism for exciton flow considering that the FRET process significantly depends on the density of excited donors and unexcited acceptors 14,15 . Colloidal quantum wells (CQWs) with high quantum efficiency, a tuneable energy bandgap, and solution processability have recently attracted broad research interest for optoelectronic devices [16][17][18][19] . Particularly, CQWs have exhibited robust excitons at room temperature with a binding energy up to 150 meV 16,18 , extraordinary optical gain performance 19,20 , and near-unity FRET efficiency 10,21 , making them promising as an ideal platform to achieve all-optical control of exciton flow using FRET.…”

Luminescent Microthermometry of Laser Heating Using Semiconductor Nanoplatelets

“…Nanoplatelets may appear attractive competitors to QD as luminescent probes, because of their narrow luminescence spectrum, reduced inhomogeneous broadening and a suppressed Auger recombination [4]. The band gap has a negative thermal coefficient (dE g /dT) and its behavior at different temperatures can be described by Varshni's empirical expression [5].…”