Cascade upconversion of photoluminescence in quantum dot ensembles

Abstract

We present a theoretical model and Monte Carlo simulation results that naturally explain all the features of the thermally activated photoluminescence upconversion effect ͓also known as anti-Stokes photoluminescence ͑ASPL͔͒ observed in ensembles of colloidal semiconductor nanocrystal quantum dots ͑QDs͒. The proposed ASPL mechanism includes the following principal ingredients: ͑i͒ optical-phonon-assisted absorption of an incident photon in a relatively large dot in the ensemble, ͑ii͒ emission of a higher-energy photon from the zero-phonon exciton-polaron state, with an upconversion equal to one optical-phonon energy, and ͑iii͒ cascade reabsorption and re-emission processes involving QDs of successively smaller sizes within the sample, rendering the experimentally observed large anti-Stokes shift of the energy of the photon that finally leaves the sample. The results obtained by the Monte Carlo modeling based on the proposed mechanism reproduce all the experimentally observed ASPL trends in colloidal QD solutions.

Anti‐Stokes cooling in semiconductor nanocrystal quantum dots: A feasibility study

“…Of course, there are “‐ n LO” and “ n LO” satellites with $n > {\rm 1}$ in the QD spectra, but their intensities are much too low for realistic values of the electron–phonon coupling constants 47. A clue to the understanding of the large anti‐Stokes shift is the experimentally established fact that the ASPL can occur only in samples with a sufficiently long optical pathway, implying that it is a result of several consecutive up‐conversion events occurring in different QDs within the sample 84.…”

Bound polaron in a quantum pseudodot under Rashba effect

“…With recent rapid advances of modern technology like molecular beam epitaxy and metal-organic vapour deposition, the investigation of low-dimensional quantum structures have aroused great interest in theory and experiment [1][2][3][4]. Examples of low-dimensional quantum structures are quantum wells, quantum wires, quantum dots and quantum pseudodots.…”

Temperature and impurity effects of the polaron in an asymmetric quantum dot

“…On the basis of the effective mass approximation, the Hamiltonian of the electron-LO phonon interaction system with a hydrogenic impurity at the center can be written as (1) where ( , ), …”

“…Due to the small structures of QDs, some physical properties such as optical and electron transport characteristics are quite different from those of the bulk material. Consequently, there has been a large amount of experimental work [1][2][3][4] on QDs. Many investigators have studied the properties of the QDs in many aspects by a variety of theoretical methods [5][6][7][8].…”