Hydrogenated amorphous carbon films (a-C:H) were prepared by r.f. glow discharge deposition from C

6

H

5

CH

3

. The PL spectra and the Excitation energy dependence of the spectra were measured at room temperature using monochromatic light of 2.9-4.5eV for studying electronic structure. The PL spectra show featureless and very broad band (FWHM is about 0.8eV).From the plot that the peak energy E

PL

versus Ecitation energy E

x

data

we identified two approximately linear regions

one with constant E

PL

at high E

x

and the other with a slope of 0.25. By assuming the Exponential density of localized states of band tails

considering two types of transitions of the carriers

the PL of a-C:H can be Eplained.One transition is that carriers make nonradiative transition from shallower to deeper states to lower energy or from deeper to shallower states because of thermal Excitation among the localized states of a band tail.Another transition is recombination among the localized states of different tails. The rates of two types of transitions are dependent on degree of localization of initial and final states. The deeplier state trapped

the less is the rate. Based on this model

the very broad band of the PL spectra is due to distribution of carriers on some energy region of broad band tail states.The red shift of the spectra with decreasing E

x

Excitation energy at sub-gap energy

can be obtained easily from distribution of carriers shifting to the deeper tail states. By the model we calculate the shape of the spectra and its changes with E

x

.