Up- and down-conversion in molecules and materials

The conversion of energy within materials has many applications. If one could convert the energy of a blue photon into two lower-energy particles, or into two red photons, solar cells could be fabricated much more efficiently. On the other hand, if one could combine the energy of two particles to form higher-energy particles, it could be used to activate a chemical reaction, for example, releasing a drug or sensitizing a standard silicon camera for infrared light.