Nanocrystal ZnS:Mn phosphor has been prepared by sol method using inorganic materials at room temperature. The nanocrystal phosphor of ZnS:Mn has cubic crystal structure with average 3nm of particle size

emitting bright orange light at peak wavelength 608nm with the full width of half maximum 75nm under UV 365nm excitation

and the brightness as high as the corresponding bulk pure cubic ZnS:Mn phosphor. According to the results reported by R.N.Bhargava

in comparison with the bulk ZnS:Mn phosphor the nanocrystal ZnS:Mn has nearly high luminescent efficiency with its luminescent decay time at least 5 orders of magnitude faster. It means that the oscillator intensity of luminescent centers in nanocrystal ZnS:Mn enhances at least 5 orders of magnitude than that in corresponding bulk ZnS:Mn. The discovery of high luminescent efficiency nanocrystal phosphor ZnS:Mn aroused the great interest to lots of researchers in the world. But these results are difficult to explain according to the normal concept. So checking these results by experiment has very important meaning in theory and experiment. In this paper the main purpose is to make a luminescent decay comparison between the nanocrystal and normal bulk crystal (particle size in micrometer) ZnS:Mn phosphors. In this comparison we controlled two factors:(1) The nanometer and bulk ones need have same crystal structure. A commercial bulk ZnS:Mn phosphor usually has mixed structure of cubic and hexagonal crystal which mainly depends on the sintering temperature and the doping concentration of luminescent activator Mn

2+

. In our experiments

under two different sintering conditions we prepared the bulk phosphors in two pure structures

cubic and hexagonal

respectively. These bulk crystal ZnS:Mn phosphors have the average particle size in micrometer order of magnitude. (2) Luminescent decay will sensitively depend upon the excitation condition

such as excitation intensity and mode like photoluminescence (PL) and cathodeluminescence (CL). In general

high intensity excitation will cause faster decay and CL will also cause faster decay than PL for the same phosphors. So in our experiments

the photoluminescent decay comparison between nanocrystal and bulk crystal ZnS:Mn was made in the same excitation condition. Under the excitation of the fourfold frequency pulse laser of Nd:YAG at 266nm (pulse width:9ns

pulse repeat frequency:3～30Hz

single pulse energy in 1.064μm:750 mJ)

we have carefully investigated the decay time of nanocrystal cubic ZnS:Mn phosphor in comparison with that of pure cubic and pure hexagonal microcrystal bulk ZnS:Mn phosphors. The 1/e luminescent decay times of these phosphors are as follows:(1) Pure cubic nanocrystal ZnS:Mn has two distinct exponential decays. The two decay time constants are 186 and 1 078μs and its amplitude ratio is 4:1; so the former is major one

which determines the 1/e decay time. (2) For pure cubic bulk crystal ZnS:Mn

there is only one exponential decay

the decay time constant is 944μs. (3) For pure hexagonal bulk ZnS:Mn

one exponential decay time constant is 1.2ms and a small amplitude hyperbolic component having extremely long decay time. These results show that the nanocrystal ZnS:Mn phosphor do have shorter photoluminescent decay time than the corresponding bulk crystal ZnS:Mn phosphors (no matter hexagonal or cubic one)

but the shortened rate is only several times

not 5 orders of magnitude.