The invention provides methods, devices and systems for excimer fluorescence energy conversion from isotopes. Unprocessed spent nuclear fuel can be used as an isotope, and processed spent nuclear fuel can be used as an isotope. A method includes placing an excimer in the path of radiation decay from the isotope. The excimer is selected according to the isotope to absorb the radiation decay and emit photons in response. Surrounding environment is shielded from the radiation decay. Photons generated from the fluorescence of the excimer are received with photovoltaic material to generate electrical energy. The electrical energy is applied to a load. Systems of the invention can be based upon spent storage casks and handle unprocessed spent nuclear fuel, or can be greatly reduced in size and handle processed fuel, with single isotope isolation allowing consumer battery sized systems.