Abstract: A colloid comprising a plurality of nanocrystals, each nanocrystal comprising rubidium, a group 11 element of the Periodic Table of Elements such as copper, silver or gold, and a halogen. A method for preparing said colloid via a room temperature ligand assisted re-precipitation (LAPP) method, wherein the ligand is an acidic ligand such as oleic acid. The precursor solution is formed in a polar organic solvent such as DMSO or DMF, and the precursor solution is contacted with a non-polar organic solvent and said ligand to precipitate the nanocrystals. A polymer comprising a plurality of nanocrystals, each nanocrystal having a particle size in the range of 1 nm to 50 nm; and a use of said colloid in optoelectronic devices, etc. are also disclosed.