Semiconductor nanocrystals known as quantum dots (QD) are caged by being associated with a molecule such as an orth-Nitrobenzyl (ONB) group. The luminescence of the QD is suppressed until activated by violet or ultra violet light.
 This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by Work at the Molecular Foundry and was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the U.S. Department of Energy. The United States Government has certain rights in this invention.