Spectral and optical properties of high-optical-quality organic glasses under prolonged ultraviolet irradiation

The effect of prolonged UV irradiation on optical and spectral luminescent properties of two types of high-quality optical organic glasses are studied by electronic absorption spectroscopy, spectrofluorimetry, IR spectroscopy, and atomic force microscopy. Glasses 2.3 mm in thickness are obtained through the layer-by-layer photopolymerization of an oligo(epoxy diacrylate) mixture with benzyl methacrylate and oligo(carbonate dimethacrylate). After the addition of europium tris(benzoyltrifluoroacetonate) to the photopolymerizing compositions, glasses that luminesce in the red spectral region are produced. The action of light gives rise to a slow photodecomposition of the luminescent component and causes a decline in the intensity of the band due to ⁵ D ₀ → ⁷ F ₂ transition of the europium cation. The growth of absorption in the yellow-green spectral region favors formation of an internal light filter; as a result, the photodecomposition of the europium complex in deep layers proceeds at a smaller rate than that in surface layers. IR-spectroscopy measurements demonstrate the accumulation of hydroxyl groups in oligo(carbonate dimethacrylate) films during irradiation in air. In an inert atmosphere, practically no photodegradation products are evolved from the matrix material.