Spectral Study of Irgacure 784 Dye in an Epoxy Resin Photopolymer

Holographic recording at shorter wavelengths enables to capture holograms with a greater resolution. Photopolymer material sensitisation to a blue or violet wavelength might require replacement of photosensitive dye or whole photosensitiser system which leads to different photoinitiation kinetics. There are known photoinitiator systems which have high values of key photoinitiation parameters, e. g., molar absorption coefficient at a broad range of wavelengths, quantum yield etc. An example of such photosensitiser is an organometallic titanocene, Irgacure 784. However Irgacure 784 in an epoxy resin photopolymer undergoes a complex photo-kinetics which is neither fully understood nor quantified. This complex photo-kinetics results in different bleaching evolution when using green and blue exposing light. The aim of this paper is to identify relevant photo-kinetic reactions taking place during exposure and driving the bleaching process. For this purpose photopolymer layers of four material compositions containing Irgacure 784 were prepared and exposed for nine exposure times. Absorbance spectrum was measured before after each exposure. We report on our experimental results and draw conclusions identifying relevant reactions of the Irgacure 784 photo-kinetics in epoxy resin photopolymers.