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2022-11-06

Since germanium has the required energy of 0.72 eV. to brake an electron free, what if a photon has say, 100 eV? would the photon (if reflected by the germanium) lose only 0.72 eV each time it hits a germanium atom, or lose more eV?

This is really two questions. The title
How much energy do photons lose when they hit a material that reflects that wavelength?
This is really two questions. The title
How much energy do photons lose when they hit a material that reflects that wavelength?
is a different problem than in the question.
Reflection means that photons elastically scatter in the center of mass system of the "material +photon". In the lab frame, the mass of the material is so large that the relativistic Doppler effect is very small, so the small loss of energy of the photon in the lab is not measureable.
The question in the body
since germanium has the required energy of 0.72 eV. to brake an electron free, what if a photon has say, 100 eV? would the photon (if reflected by the germanium) lose only 0.72 eV each time it hits a germanium atom, or lose more eV?
Is about the photoelectric effect. Reflection means elastic scattering by definition, therefore if the photoelectric effect happens there is no reflection. The total energy of the photon scatters off an electron and releases it to interact further or to leave the surface of the material. Compton scattering may also happen, and a photon may lose part of its energy to the ejected electron, but it is not a reflection.

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