North Konami provides single CsPbBr3 perovskite quantum dots

Semiconductor quantum dots have long been considered artificial atoms, but despite important similarities in strong-level quantization and single-photon emission capabilities, their emission spectra are far broader than typical atomic emission lines.



Here, by using molecular dynamics to simulate exciton-surface phonon interactions in CsPbBr3 quantum dots, and then using single quantum dot spectroscopy, researchers from Switzerland have demonstrated that the emission line broadening in these quantum dots is dominated by the interaction of excitons with Coupling control of low-energy surface phonons. A slight adjustment of the surface chemistry allows to obtain a smaller emission linewidth of 35−65 meV (compared to the initial value of 70–120 meV), which is comparable to the optimal value (20−60 meV) of structurally rigid colloidal II-VI quantum dots. Traditional light-emitting devices and emerging quantum light sources require ultra-narrow emission. The related paper was published in the journal Nature Communication with the title "Ultra-narrow room-temperature emission from single CsPbBr3 perovskite quantum dots".



Paper link:

https://doi.org/10.1038/s41467-022-30016-0

Collectively synthesized semiconductor quantum dots (QDs) are an important building block for various optoelectronic applications. After intense efforts over the past three decades, quantum dots with almost 100% photoluminescence quantum yields (PLQYs) can now be produced, with narrow size distributions and facile emission tunability across the visible spectrum. For these reasons, colloidal quantum dots have become the light emitters of choice for the latest generation of commercial LCD color displays and are actively used in light-emitting diodes, lasers, and luminescent solar concentrators. For display technology, the narrow emission spectrum of quantum dots, that is, the linewidth (also known as full width at half maximum, FWHM) of less than 200 meV (about 40 nm for InP quantum dots is green) is a key factor in entering and conquering market opportunities. This is also crucial in active pixel display technology, where OLED and QLED are the main technology solutions. A few years ago, a new material system emerged—quantum dots of perovskite-type APbX3 compounds. They have nearly 100% PL QY in solution and tunable narrow-band luminescence over the entire visible wavelength range. The high emissivity and large absorption coefficient make these quantum dots among the brightest known emitters. Its inherent defect tolerance allows these properties to be realized with maximum synthesis simplicity.



So far, these quantum dots have been used in high-efficiency LEDs approaching theoretical external quantum efficiencies (EQE>20%), as well as in solar cells, high-efficiency lasers, and high-coherence sources of single or bunched light. For example, the emission lines of isolated atoms found in atomic vapors that do not interact with any matrix are extremely narrow, limited primarily by the radiation lifetime. Conversely, when an emission state exists in a solid-state material, whether it is a localized atomic transition in a crystal host or a delocalized exciton in a semiconductor, its emission linewidth is broadened by coupling to crystal vibrations. Further complexity for individual colloidal quantum dots comes from strong quantum confinement, which splits the ground-state exciton band-edge manifold. Depending on the energy difference between these states and the temperature of the system, the emission may come from multiple electronic transitions. Furthermore, in quantum dot ensembles, structural disorder, such as size and/or compositional inhomogeneity, can further widen the emission line. Unraveling the interplay of all these mechanisms in colloidal quantum dots has been a challenge of the past 30 years. Revealing and reducing emission line broadening is important for the development of ultranarrow perovskite-based LEDs at the ensemble and single-photon levels. (Text: Aisin Gioro Star)

Figure 1. Emission line broadening in nanomaterials: the case of perovskite compounds.

Figure 2 Size-dependent emission line broadening and its origin in perovskite quantum dots.

Figure 3. Dilution-induced surface modification of CsPbBr3 quantum dots.