A model describing surface quenching of isolated ion centres in nanocrystaJs is proposed based on the energy transfer between the doped ions and the nanocrystalline surface quenching centres.The quenching rate depends on the position of the ions in the nanocrystal,hence the decay curve under non-selective excitation is generally nonexponential.The decay curve calculated with this model is in good agreement with that of the 4T1→6A1 emission in ZnS:Mn2+ nanocrystals.