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Given a high enough temperature, or a high enough electrical field, can we make every material emit visible light?

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    $\begingroup$ any material emits some light at any temperature, the spectrum is contninuous $\endgroup$ – Aksakal Mar 3 '14 at 19:34
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"emit visible light" Selection rules! First Law. A clean, pure, transparent and colorless monocrystal diamond has a Debye temperature around 2230 K. Heating diamond to 1000 C (1273 K) does not render it luminous in the visible. Diamond optical absorption edge vs. photon energy at different temperatures, and with various impurities ((1) is intrinsic),

http://www.ioffe.ru/SVA/NSM/Semicond/Diamond/optic.html

enter image description here

(Isotopically pure C-12 diamond will be more extreme. Diamond is kinetically labile to graphite beginning around 1000 C in air. Under inert gas or a mildly reducing atomsphere, it lasts until about 1500 C.)

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  • $\begingroup$ Does "kinetically labile" mean a "gradual" phase change? Could you elaborate on the details? $\endgroup$ – hyportnex Mar 4 '14 at 3:18
  • $\begingroup$ I don't follow your reasoning; maybe I can learn something. How does the Debye temperature or the electronic absorption edge make your argument? $\endgroup$ – garyp Mar 4 '14 at 3:28
  • $\begingroup$ Graphite to diamond is nearly explosive at temp. The activation energy for that conversion is almost the lattice dissociation energy. Everything sits there, then there is a nucleation center, then it pops. At low temps, diamond drilling into ferrous metal uncreates the cutting edge. Frsit Lwse - a body must absorb and emit identically at a given wavelength. Transparent is a terrible emitter. $\endgroup$ – Uncle Al Mar 4 '14 at 20:38
  • $\begingroup$ @Uncle Ai. Thanks for sharing. However, I really dont understand. And because of the way you write it is really hard for me to dive into it. Which "selection rules". Which "first law"? What is (1) referrring to and what is it you are calling "intrinsic"? It seems like you are writing to a colleague who is already an expert, but most readers are far from. $\endgroup$ – Mads Skjern Jul 27 at 1:51
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Yes. Every object whose temperature is not 0 K radiates. That means that every object glows in a sense. For everyday objects at everyday temperatures, the wavelength of the glow is around $10\, \mu m$, far in the infrared, and far outside the range of human vision. As you heat the object, the wavelength of the radiation gets closer and closer to the visible range. Any object will eventually get hot enough that the glow will become visible, if it hasn't burst into flames first.

Electric field will not cause an object to "glow", but in a strong enough electric field electrons will be pulled from the object, and light will be emitted by various mechanisms, some not directly connected to the object. In gases, the light can be continuous and might be described a a "glow". Most of the time, though, I think I would call the light emitted in an electric field as a "spark", but there are a lot of different situations, and the light will be different in each situation.

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  • $\begingroup$ It could glow and burst into flames :-). $\endgroup$ – Carl Witthoft Mar 3 '14 at 19:43
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    $\begingroup$ the glow does not have a single wavelength, that would not be thermal radiation otherwise. the glow covers entire spectrum, it's just the intensity in visible spectrum is so low that an eye doesn't notice it $\endgroup$ – Aksakal Mar 3 '14 at 19:56
  • $\begingroup$ Nonsense. Guess why sun light passes down to earth and reemitted heat radiation from earth is not absorbed by nitrogen or oxygen. Guess why a flame of hydrogen is nearly invisible. $\endgroup$ – Georg Mar 3 '14 at 20:19
  • $\begingroup$ @Georg I seem to be a little slow. Can you elaborate? $\endgroup$ – garyp Mar 4 '14 at 3:29
  • $\begingroup$ I believe @Georg is pointing out that nitrogen and oxygen (and hydrogen) cannot emit or absorb visible light and thus no matter how hot you get pure nitrogen or oxygen it will not glow, and thus is a counterexample to this answer. $\endgroup$ – Rick Oct 19 '15 at 15:59

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