Wikipedia:Reference desk/Archives/Science/2017 July 27

= July 27 =

Television (What is the relationship between QLED and Quantum Mechanics?)
What is the relationship between QLED and Quantum Mechanics? 196.192.183.14 (talk) 20:29, 27 July 2017 (UTC)
 * Not sure offhand for modern QLEDs, but in the mid-80s I worked (briefly!) as a quantum mechanic (tiny, tiny spanners). I designed a laser diode. Specifically a quantum well heterostructure. It's not hard to make "a laser diode". You look up the properties of some semiconductor compounds, brewing up the mixture to give band gap energies that you like, and a frequency $$f$$ (thus implicitly the wavelength $$\lambda$$) that depends on the photon energy $$E$$ produced by jumping between those bands, according to Planck and $$E=hf$$, where $$h$$ is Planck's constant.
 * Now the problem. Sometimes you want a particular wavelength (we wanted one that was minimally absorbed by glass optical fibres). Maybe you're making LEDs to make a coloured display. Maybe you just want a precisely monochromatic colour to be a more efficient way of generating useful light. But no matter how hard you look, you can't find any combination of chemistry that delivers what you need.
 * Enter the quantum well. This is a structure made of less-fussy materials, where its quantum behaviour (i.e. the band gaps) are controlled by the dimensions of the well (and the effects of QM behaviour), not just the chemistry. With a precisely controlled manufacturing process (difficult back then, but achievable) you can control these thicknesses. Voila, a metamaterial with effective properties of whatever you like (within limits). Now you have a choice of wavelength, not just a choice from a few naturally available ones. Andy Dingley (talk) 20:50, 27 July 2017 (UTC)


 * See quantum dot and quantum dot display. Gandalf61 (talk) 20:52, 27 July 2017 (UTC)
 * Note that all LEDs, and for that matter all semiconductor devices, involve quantum mechanics. Quantum mechanics is required to explain most of the properties of semiconductors. --47.138.161.183 (talk) 23:12, 28 July 2017 (UTC)
 * There is an important difference though between QM as a description of naturally occurring semiconductor materials, and as a means of designing new metamaterials with previous unattainable properties. Andy Dingley (talk) 14:14, 30 July 2017 (UTC)