The photoluminescent intensities of nanocrystal ZnS:Tb and ZnS:Eu synthesized using a new technique were 2.5 and 2.8 times higher than those of bulk phosphors. Taking charge compensation into account, the luminescent efficiency of the nanocrystals can be improved. The cathodoluminescence of the nanocrystals was observed for the first time. These nanocrystal phosphors are promising for field emission display, electroluminescence, plasma-display panels, and cathode ray tubes.