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For example, it took over 3 decades to create efficient blue LEDs in the lab after the red and green leds were discovered. For OLED displays as well, the red and green pixels are phosphorescent oleds while the blue is a flourescent oled which has a shorter lifetime. In addition, tvs using quantum dot conversion/color filters only use a combination of red and green quantum dots, but no blue quantum dots. In self emissive electroluminescent displays(ELQD), the major challenge to commercializing this display is that the blue quantum dot lifetime still lags far behind the red and green.

Some related articles: https://www.nature.com/articles/s41566-022-00958-4

https://sid.onlinelibrary.wiley.com/doi/epdf/10.1002/jsid.1126

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    $\begingroup$ More complex materials, lack of confidence in highly defected materials with short lifetimes (that still could be gotten to work), no major driving force in application space (until they existed), ... Pretty typical exploratory research to volume production course, actually. $\endgroup$
    – Jon Custer
    Commented Jul 26, 2022 at 15:45
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    $\begingroup$ The fact that blue requires a larger band gap material than green or red is surely relevant. Why we that requires materials that are more difficult to work with, I can't say. For quantum dots, the dots would need an even higher band-gap material to live in. $\endgroup$
    – The Photon
    Commented Jul 26, 2022 at 15:55

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There are a lot of questions packed into one here. I'll address only one:

In the case of LED's, as pointed out by The Photon and hinted at by Jon Custer, the problem getting blue was that the appropriate band gap which would produce blue light directly (as in the case of the original red LED) couldn't be engineered from a materials science standpoint.

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    $\begingroup$ Specifically, the problem was it was difficult to grow p-doped wide-bandgap semiconductors like GaN and AlGaN, which are needed for the P-N junctions and heterostructures in LEDs (they are naturally n-doped). Quantum dots are another kind of solid-state LED, which face the same problem. $\endgroup$
    – Gilbert
    Commented Jul 27, 2022 at 11:49

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