Luminescent inorganic nanocrystals - quantum dots (QDs or Q-dots). The emission wavelength is a function of the crystal size or structure - crystals of the same chemistry can have the emission maxima in a wide range.
Hydrophilic QDs are coated with -COOH groups and can be easily used for labeling purposes for chemical and biological applications.
CdSe/ZnS, ZnCdSe/ZnS, ZnCuInS/ZnS (core/shell type), and perovskite Q-dots are available as hydrophobic and hydrophilic modifications.
QDs can be supplied up to kilogram quantities.