The Nanosys view on the state of electroluminescent quantum dots: Page 3 of 5

June 20, 2019 //By Chris Chinnock
quantum dots
Quantum Dots are amazing particles. They can emit light when pumped with higher energy light (photoluminescent). They can emit electrons when pumped with light (photoelectric) and they can emit light when pumped with electrons (electroluminescent). I want to talk about this latter use, ELQDs, in this article.

Note in the lifetime data shown in figure 2 that the vertical axis is the time to reach 50% of the initial luminance, a common metric for determining commercial viability. This data is only at 100 nits, a level too low for most applications, however, to be fair, most groups report results at this level so it makes for better comparison. A more typical luminance level of 500 nits is more representative, but lifetime degrade much more quickly at this level – “and not in a linear way,” says Hartlove.

Fig. 2: ELQD materials lifetime data. The vertical axis is the
time to reach 50% of the initial luminance.

Hartlove didn’t say what the lifetime might be at elevated luminance levels but he references TADF developments for OLEDs where blue lifetimes are in the 5-30 hour range for higher luminance levels. He thinks their team can get to this level in about a year as well.

Nanosys is focused on developing a blue ELQD composed of a ZnTeSe alloy that allows for blue emission in the 450-460 nm range. InP-based QD can be pushed down to 460nm but with very low quantum yield (~40%). ZnSe quantum dots can be pushed upward to maybe 450 but with a similar low quantum yield.  By building a quantum dot with a little Tellurium in the ZnSe core, transitioning to ZnSe and then to ZnS, Nanosys can achieve blue light at 451nm with 80% quantum yield and a FWHM of 21 nm – all very acceptable values.

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