A method of emitting photons at a desired wavelength, including: providing a material having a first region of high absorption of radiation at a first set of wavelength of radiation, contiguous with a second region of low absorption of radiation at a shorter set of wavelengths, and a third region of high emission at a further shorter set of wavelengths; applying energy to the material at the first region, such that most of an effective black body radiation of said material at a temperature of the material would fall within the second region and be configured to transfer energy to said third region and not overlap with the first region; and emitting energy from the material at the third region, powered by said applying energy.