Photophysics of Thermally-Assisted Photobleaching in “Giant” Quantum Dots Revealed in Single Nanocrystals

Abstract

Quantum dots (QDs) are steadily being implemented as down-conversion phosphors in market-ready display products to enhance color rendering, brightness, and energy efficiency. However, for adequate longevity, QDs must be encased in a protective barrier that separates them from ambient oxygen and humidity, and device architectures are designed to avoid significant heating of the QDs as well as direct contact between the QDs and the excitation source. In order to increase the utility of QDs in display technologies and to extend their usefulness to more demanding applications as, for example, alternative phosphors for solid-state lighting (SSL), QDs must retain their photoluminescence emission properties over extended periods of time under conditions of high temperature and high light flux. Doing so would simplify the fabrication costs for QD display technologies and enable QDs to be used as down-conversion materials in light-emitting diodes for SSL, where direct-on-chip configurations expose the emitters to temperatures approaching 100 °C and to photon fluxes from 0.1 W/mm to potentially 10 W/mm. Here, we investigate the photobleaching processes of single QDs exposed to controlled temperature and photon flux. In particular, we investigate two types of room-temperature-stable core/thick-shell QDs, known as "giant" QDs for which shell growth is conducted using either a standard layer-by-layer technique or by a continuous injection method. We determine the mechanistic pathways responsible for thermally-assisted photodegradation, distinguishing effects of hot-carrier trapping and QD charging. The findings presented here will assist in the further development of advanced QD heterostructures for maximum device lifetime stability.

Reducing the Chromaticity Shifts of Light‐Emitting Diodes Using Gradient‐Alloyed CdxZn1−xSeyS1−y@ZnS Core Shell Quantum Dots with Enhanced High‐Temperature Photoluminescence

“…[9b,22] Core shell structure confines the wave function of electrons and holes distributed in the core . It has been well known that the exciton recombination can be disturbed by nonradiative recombination through trap defects at the core shell interface and/or shell surface . The gradient core shell of Cd x Zn 1− x Se y S 1− y @ZnS QDs can greatly reduce lattice mismatch induced interfacial trap defects.…”

Cation/Anion Exchange Reactions toward the Syntheses of Upgraded Nanostructures: Principles and Applications

“…138 Further Pb-based core-shell QDs with enhanced PL properties enabled by CER and ion diffusion were also reported by Hollingsworth and colleagues. 148,149 Based on a partial CER and ligand-induced phase selection, PbSe@CdSe thick-shelled QDs synthesized in 1-octadecene exhibited a bright and stable PL. 149 Different from core-shell QDs with fully separated core and shell components, engineered ion diffusion in core-shell QDs enabled continuously graded shells, which exhibited enhanced quantum yields (Figure 8C).…”

Twist Angle-Dependent Interlayer Exciton Lifetimes in van der Waals Heterostructures

“…Using a rate equation analysis for a three-level system (see SM for details, which includes Refs. [45][46][47][48]), we attribute the fast (slow) decay component to the lifetime of the bright (dark) exciton assuming the scattering rate between the bright and dark state is slower than the bright exciton lifetime. In all samples, we observe shorter IX lifetimes as the energy of the resonance increases as shown in the inset to each panel in Figs.…”