Researchers using the Canadian Light Source (CLS) at the University of Saskatchewan have made a breakthrough in blue quantum dot fluorescence.

Quantum dots are nanocrystals that glow and, when they glow, they creates very pure light in a precise wavelength of red, blue or green.

Blue-glowing quantum dots have proved particularly challenging for researchers.

However, University of Toronto (U of T) researcher Dr. Yitong Dong and collaborators have recently made  significant progress in blue quantum dot fluorescence.

The research has great significance for the colour quality in future LED-based displays.

The abstract of their paper reads:

Colloidal quantum dot (QD) solids are emerging semiconductors that have been actively explored in fundamental studies of charge transport1 and for applications in optoelectronics.

Forming high-quality QD solids—necessary for device fabrication—requires substitution of the long organic ligands used for synthesis with short ligands that provide increased QD coupling and improved charge transport.

However, in perovskite QDs, the polar solvents used to carry out the ligand exchange decompose the highly ionic perovskites.

Here we report perovskite QD resurfacing to achieve a bipolar shell consisting of an inner anion shell, and an outer shell comprised of cations and polar solvent molecules. The outer shell is electrostatically adsorbed to the negatively charged inner shell. This approach produces strongly confined perovskite

QD solids that feature improved carrier mobility (≥0.01 cm2 V−1 s−1) and reduced trap density relative to previously reported low-dimensional perovskites.

Blue-emitting QD films exhibit photoluminescence quantum yields exceeding 90%. By exploiting the improved mobility, we have been able to fabricate CsPbBr3 QD-based efficient blue and green light-emitting diodes.

Blue devices with reduced trap density have an external quantum efficiency of 12.3%; the green devices achieve an external quantum efficiency of 22%.