Abstract
We have measured the normal reflection spectrum of (1
1
0) cleaved faces of single crystals of CuI in the spectral range of the Z
12(3058 meV) and Z
3(3699 meV) exciton lines at the temperature of 95 K. We have fitted the experimental data by computing a non local dielectric function and taken into account various additional boundary conditions (ABC) as well as the dead layer model in a semi-infinite crystal. A quantitative agreement is obtained assuming the following values for the background dielectric constant
ε
∞=7.2 and for the effective masses of the excitons
M(Z
12)=1.8 m
0,
M(Z
3)=0.5 m
0. These results do not depend on the choice of a particular ABC. The longitudinal-transverse exciton splitting energies deduced from the fit are:
ω
LT (Z
12)=5.9 meV and
ω
LT (Z
3)=2 meV.