In present paper

we study the difference of electroluminescence (EL) spectra of ZnS:Ho

3+

and ZnS:HoF

3

ACEL thin films. ZnS:Ho

3+

and ZnS: HoF

3

thin films are deposited by two separete boats in vacuum.The mechanism of EL excitation in ZnS:Ho

3+

is discussed. The ratio of shorter wavelength emission intensity (490mn) to longer one (550nm) increases with applied voltage

shown as in Fig.3

we suggest that the EL in ZnS thin film doped with Ho

3+

is generated by impact excitation of hot electrons. According to the EL decay behaviors of blue emission around 490nm (labled

I

b

) and red emission around 660 nm (labled

I

d

)

as shown in Fig. 4 and Table 1. it is indicated that the emissions of

I

b

and

I

d

are the transitions from the same excited state 5F

3

when the concentration of Ho

3+

ions is lower.