So some things electrons remain in exited states for longer amount of times? Explain how this happens please.It takes time for the energy of a system to change. It might help to get an intuitive feeling for what that energy really is; it's the kinetic energy of the molecules contained in sand. When rays of sun light hit the sand, some of the energy contained in the light is transferred into the sand, causing these sand molecules to "jiggle" and to feel hot to the touch. When the sun sets and no more rays of sunlight are available to keep the sand molecules "jiggling", the jiggling slows down over time, for a variety of reasons; some of that energy in the sand is transferred into the ground, into the air, etc...
It seems like you're equating the thermal radiation with a spontaneous emission process. It's not like the sand is a semiconductor with a band gap in the IR. The atoms in the sand have some kinetic energy, and over time they lose this by colliding with other atoms in the sand. Some of these collisions will result in the energy being released as radiation. You have charges accelerating, and this requires radiation.So some things electrons remain in exited states for longer amount of times? Explain how this happens please.
I understand, but then why doesn't a liquid do this?Well, I have learned something more. Solid bodies give off broad-band (continuous) emissions and gases and vaporized material give off characteristic spectral emissions. For someone who worked on flame photometers years ago you would think I would have realized the difference, but I hadn't really thought about it before.
So if LA is still with us after all this I think the simplified answer is: The heat vibrations/oscillations, whatever they might be, in the sand, transfer energy back and forth in the body of the sand but only the surface radiates into "space." Then the warmer material underneath the surface reheats the surface material and then more heat is radiated outward. All this time the atoms in the material are passing heat energy back and forth throughout the material below the surface.
Bottom line; it takes time for the energy to be passed between the atoms and reach the surface where it can be radiated.
I think I have learned enough on this subject for a while.