Question

There are materials which absorb photons of shorter wavelength and emit photons of longer wavelength. Can there be stable substances which absorb photons of larger wavelength and emit light of shorter wavelength?

Answer 1

Energy of photon of shorter wavelength will be high according to $E=\frac{hc}{\lambda }$ and energy of photon of longer wavelength will be low.

So, when the materials which absorb photons of shorter wavelength and emit photon of longer wavelength, the energy given out is less than the energy supplied.

But in second case, the energy of the incident photon is low for the substances which has to absorb photons of larger wavelength and energy of emitted photon is high to emit light of shorter wavelength. This will be happening only when the material has to supply the energy for the emission of photon.

But this is not possible for a stable substance.

Final answer: No