Originally scheduled for March of 2020, the virtual QD Forum and Phosphor Global Summit went off without a hitch in early November this year. What I love about this conference is the mix of industry professionals, super-smart academics, and startups with new ideas. It’s a much more manageable conference too, usually a few hundred people so the networking is excellent, with a focus on those in the QD and Phosphor industry.
The talks were meaty, and the interactive Q&A were pretty good too. I’ve boiled it down to a few topics that caught my eye this year, some of which came as a surprise to me.
The new-kid-on-the-block is not so little anymore. With a clear value proposition and multiple companies developing products leveraging pervoskite technology, this material is rapidly maturing. The ultra-narrow green emission (~20 nm), high efficiency, and high absorption of blue light make this material match wonderfully with KSF red phosphor for a bright and colorful display.
Avantama has been promoting their perovskite material for a few years now, and this year the message was clear. It is ready for prime time. According to the CEO, their pilot film product has passed customer tests and is ready for adoption. When integrated into a monitor with KSF it achieved >90% rec 2020, with >2000 nits brightness. Not sure I would opt for full brightness settings at my workstation, but for some applications (like professional monitors) these are metrics are excellent.
A newcomer on the scene, Nanopattern Technologies, is developing special ligands on the QD surface that are both photo-patternable (think photolithography) and removable, resulting in very high density QD films. This could be ideal for QD-EL, as well as QD-color converters technology with blue micro LEDs or OLED backlights. They demonstrated extremely high absorption in a very thin film using perovskites QDs. The challenge will be packing a high density of QDs together while maintaining the performance that display-makers rely on. This can be a challenge due to interactions between neighboring QDs which can essentially “turn off” the QD emission. I look forward to seeing more from Nanopattern in the future.
At this point I know you are all thinking about lead. Yes, all of these perovskite materials contain lead. And yes, lead is restricted in the EU under RoHS to a level of 1000 ppm. The proposed perovskite film technology will most likely fall under the 1000 ppm limit; however it is the future technology (QD color converter/color filter in particular) that causes me pause. At high QD loading there is potential to exceed the 1000 ppm limit, making perovskites a no-go in many parts of the world.
On Chip is back?
This one caught me a little off guard to be honest. With all the talk of next-gen QD technology, I thought most people had given up on QDs on chip. Trust me, it is hard to do (this was my job for 2 years). At least in the lighting world, it seems QDs on chip still have potential.
Osram presented a status update on their LEDs containing red QDs (and other phosphors) on a blue LED for high efficacy and very good color. You should know that this is a Cd-based QD, and in lighting the restriction of 100 ppm is still in play, so Osram has to mix it with other red phosphors in order to keep the Cd content in check. Still, it’s a great demonstration that QDs can survive in these extremely harsh conditions (when properly designed).
Newcomer QustomDot shared their vision for Cd-free QDs on chip, with a focus on enabling microLED color conversion… a worthy goal. They leverage a new synthesis strategy (still InP-based though) which comes from the group of famed QD researcher professor Zeger Hens at the University of Ghent. Time will tell if they have what it takes to make it on chip!
An important development outside of the QD Forum is the recent news that KSF has now been licensed to Nichia for general lighting (it already was for displays). This may throw a wrench into the plans of these companies developing QD tech for lighting as it signals a shift in strategy from GE who was holding KSF close to the vest for their own lighting products. Now that Nichia (and more to follow I suspect) are supplying LEDs containing KSF, any luminaire manufacturer in the world can make lighting products containing KSF LEDs.
There were a few talks with a focus on nanophosphors which caught my eye. Traditionally nanophosphors have not been successful because their optical properties at the nanoscale suffer tremendously compared to the micro-sized equivalents. This is mainly due to surface defects and challenges with making the materials in high quality at sizes <100 nm which is why QDs have always held a distinct advantage at this size scale. But that hasn’t stopped the development from happening.
Seaborough (Netherlands) demonstrated a proof-of-concept for enhancing Eu3+ doped phosphors which typically do not absorb blue LED light very well. In their strategy, they paired a Eu3+ nanophosphor with a different absorber; YAG nanophosphor. The YAG phosphor actually isn’t acting as a phosphor, it is acting as an absorber of blue light, then transferring the energy to the red-emitting Eu3+ phosphor. In the photo below you can see that when the two are paired together at the nanoscale (nano-engineered) the emission is bright red. This is in stark contrast to when the two phosphors are mixed at the macro scale (conventional) which shows emission dominated from the YAG phosphor (green in this case due to Tb dopant in the YAG system). The nano-engineered approach which leverages energy transfer from one nanophosphor to the next can potentially be a nice narrow red emission peak desirable for general lighting. It may not be an approach that works for displays unless scientists can improve the energy transfer efficiency, as these samples also show a healthy amount of different colors besides red.