The spontaneous emission of photons by an atom placed near the dielect
ric slab is analyzed using global free electromagnetic modes, satisfyi
ng necessary continuity conditions at the slab boundaries. These modes
include the modes extended over the whole space (traveling) and the m
odes trapped to a waveguide formed by the slab (trapped). To describe
angular properties of spontaneous emission a parametrization of the tr
aveling modes by the outgoing waves has been proposed. Angular charact
eristics of the traveling photon emission, distributions of the trappe
d photon emission, as well as global decay rates have been calculated
using the quantum approach and standard perturbation theory. Enhanceme
nt and suppression of radiative decay rates in various configurations
have been shown. A certain calculational error in an earlier paper by
Khosravi and Loudon [Proc. R. Soc. London Ser. A 438, 373 (1992)] affe
cting thin slabs and results near waveguide-mode thresholds has been i
mproved.