A method is described to functionalize specifically the interior portions of polyolefinic films with chromophoric/lumophoric groups. In the first step, a film doped with dibenzothiophene 5-oxide (DBTO) is irradiated (lambda > 300 nn) to produce O(P-3) atoms that oxidize nearby C-H bonds of the polymer. Covalent attachment of acid chlorides (containing chromophoric/lumophoric groups) to the hydroxy bonds (via ester linkages) provides films that retain their absorption and luminescence in water or air for long periods. The esterified films have been characterized using UV/vis absorption spectroscopy and static and dynamic fluorescence techniques, Fluorescence from native or modified and then esterified films in 1.0 M methanolic 2-(dimethylamino)ethanol, a surface quencher, indicates that the vast majority of the chromophores/lumophores are located inside the films. Selective modification of the film surfaces by an analogous method was not efficient. However, avery low concentration of hydroxy groups is present throughout the native films. Their esterification reduces the fluorescence contrast between undoped/irradiated and DBTO-doped/irradiated parts of a film.