a method of producing a lasing microsource of colloidal nanocrystals . the method includes the steps of preparing a nanocrystal solution in a solvent ; depositing at least a drop of the nanocrystals solution with a drop volume below 1 nl on a flat substrate ; and evaporating the solvent to dryness thereby to obtain at the edge of the evaporated drop a single annular stripe including a domain wherein the nanocrystals are arranged in an ordered array , wherein the ordered nanocrystals in the domain constitute an active region capable of lasing and the radially inner and outer edges of the stripe define a resonant cavity in which the active region is inserted .