Quantum Dots Ken Warner (Interesting Read) A lo

Quantum Dots Ken Warner (Interesting Read)

A lot of the conversation about quantum dots at Display Week this year revolved around the European Commission’s rejection of its own technical committee’s recommendation that cadmium-based quantum dots continue to be exempt from prohibition because cadmium is on the European list of dangerous substances.

Initially, this generated some angst in the cadmium contingent and some jubilation in the non-cadmium (mostly indium phosphide) crowd. But a consensus soon emerged that the EC’s rejection was based on one minor technical and one procedural matter and that the technical committee would certainly correct the minor issues, after which the exemption would be continued. EC exemptions are often based on there being no alternative solution available, so the issue revolved around the current availability of indium phosphide. However, indium has also been added to the EU’s list of hazardous substances. It was generally regarded as irrelevant to the regulators that neither cadmium nor indium is biologically available when encased in a quantum-dot shell.

Nanosys, which won an award from SID for best small exhibit at the show, had three side-by-side TVs that clearly showed why indium-phosphide quantum dots (QDs) are a poor substitute for cadmium. The typical conventional LCD TV with white-LED backlighting in the Nanosys booth had a measured color gamut of less than 60% of Rec.2020, a luminance of 500 nits, and a power consumption of 130 W. The same model of TV modified with blue LEDs and a cadmium QD sheet in the backlight measured greater than 90% of Rec.2020, 400 nits, and a power consumption of 130 W (with the original color-filter array) (Fig. 3). And another example of the same model TV with an indium-phosphide QD sheet measured about 75% of Rec.2020, 350 nits, and 130 W. Clearly, if the goal is to get close to Rec.2020, indium phosphide is not the way to go. Subjectively, the difference between the cadmium QD-enhanced TV and the standard model was dramatic. The difference between the indium-phosphide-enhanced set and the standard one was visible, but sufficiently subtle that consumers might not be strongly motivated to pay a premium for it.

Nanosys Corporate Communications Manager Jeff Yurek wanted me to know that Nanosys has now reached a level of manufacturing volume such that the EPA required it to submit a pre-manufacturing notice, which was accepted. He also announced a follow-on investment from Samsung Venture Investment Corporation. The new funds will be used to expand production capacity as demand increases.

Also at Display Week, Nanosys partner 3M Display Materials and Systems Division showcased LCDs in several sizes with color gamuts of up to 93.7% of the Rec.2020 color gamut. Among the demos was a 4K monitor with 93.7% Rec.2020, which demonstrated, as the booth signage read, “one of the largest known color gamuts in an otherwise commercially available 4K LCD monitor.”

QD Vision was exhibiting available commercial products using its IQ Color linear QD element. Among these were a Philips 29-in. monitor, a TCL 65-in. TV, and a Hisense 65-in. curved TV. This is the first curved TV, said CMO John Volkmann, and it uses one edge light and one IQ Color element on each of the left and right edges.

I asked Volkmann if he was concerned that an increasing percentage of TV sets are using direct backlighting for local-area dimming and therefore cannot use QD Vision’s linear array. His answer: “There will be a lot of edge-lit TVs made for the foreseeable future.” He also said the company was looking at other form factors. As previously stated, the company is working on a QD-on-chip approach and is closer than its competitors. There was a 94% Rec.2020 demo in the booth. To get higher than that, Volkmann said, wide-gamut color-filter arrays as well as high-quality QDs (such as QD Vision’s) are required. Volkmann was confident that cadmium would remain legal in the EU and did not mention any fall-back materials for QD Vision.

If Nanosys, 3M, and QD Vision are among the leading QD companies, Quantum Materials Corp. (San Marcos, Texas) is one of the hopefuls. Although not exhibiting at Display Week, QMC announced in a June 1 press release that it had “launched their new QDX class of high-stability cadmium-free quantum dots….” The release continued, “QDX quantum dots have been tested to withstand heat resistance to 150°C for 4 hours with no oxidation performance degradation in an open-air environment.” When I asked him, QMC PR person Art Lamstein told me the company is in a “pre-revenue” stage. In addition to the company’s original cadmium-based quantum tetrapods based on a Rice University patent, QMC is now also making indium-phosphide dots based on a Bayer patent the company purchased in 2014.

Nanoco (Manchester, UK) was not on the show floor, but I spoke briefly with COO Keith Wiggins and Business Development VP Steve Reinhard. Since Nanoco has for some time emphasized that its QDs are free of not only cadmium, but also of other heavy metals, the company has been almost gleeful in welcoming the European Parliament’s decision to turn down the RoHS exemption for cadmium despite its approval by the technical committee. However, as mentioned above, the majority opinion is that this potential gift to Nanoco is likely to be short-lived. As is well known, Nanoco has licensed its technology to Dow Chemical for volume manufacturing.