A light-activated system would fit such a bill. Another application is possible in scanning tunneling or electron microscopes where the specimen is placed on a stage in high vacuum. Currently, to move specimens, investigators either shut down the system or an electric lead penetrates the vacuum chamber to power positioning equipment. Uchino suggests that a properly built platform of PLZT could be moved in the vacuum by shining light from outside, without breaching the seal. Researchers are not certain what causes this bulk photovoltaic effect.
Pure crystals produce so little current that it is unmeasurable.
The impurities in the crystal structure provide the electron and the uneven structure allows the electron, when excited, to not only increase in energy, but also move slightly. It is this movement that creates the high voltage and low current. However, if the electron in one crystal moves to the right and the next one moves left, there will be no net effect. To overcome this, the polycrystalline materials must be polarized so that, when the electrons become excited they all move in the same direction. Near-ultraviolet radiation, or black light, is the trigger for PLZT, but other photostrictive materials respond to light in other wavelengths.