When the frequency of a photon drops, the wavelength of the photon rises. There are two alternative scenarios: case one, in which the photons have a shorter wavelength and the energy is consumed against the work function, and case two, in which the photons have a longer wavelength and the energy is consumed against the work function. In scenario two, the photons may have a longer wavelength and release shorter, lower-energy photons.
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?
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?