This SO discussion here lists some chemicals (and interestingly chlorophyll) that absorb visible radiation and emit infra red. I was wondering if there were chemicals that absorbed near infra-red and emitted much larger wavelengths (near microwave).
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$\begingroup$ It does work that way. Imagine that you put 10 energy units into creating an excited state. When that excited state decays you can't get more than 10 energy units back in the emitted photon, and you generally get less. $\endgroup$– MaxWCommented Feb 10, 2016 at 20:14
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$\begingroup$ @MaxW do you know chemicals that absorb near infra-red and emit microwaves? $\endgroup$– user1155386Commented Feb 10, 2016 at 20:42
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$\begingroup$ Microwaves would be too low in energy for most (all?) electron transitions. There might be some molecule that would do that but it would be really, really weird. There are molecules (chemicals, minerals) that emit in the infrared. Absorbing in high energy infrared, and emitting a low energy infrared photon would be possible. (Don't know one off the top of my head.) $\endgroup$– MaxWCommented Feb 10, 2016 at 21:25
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$\begingroup$ What do you mean by "higher" wavelengths? Do you mean longer wavelengths (with lower energy) or did you mean higher frequencies (shorter wavelengths, higher energy). $\endgroup$– matt_blackCommented Aug 7, 2016 at 9:58
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All molecules emit in the microwave region. They all have rotational energy levels and they absorb and emit all the time as energy flows between these levels. But this not what you are asking I suspect. If you blast thin Gallium Sulphide wafers with a femtosecond laser then it is possible to generate terahertz radiation.
