by D. Cody, E. Mihaylova, L. O’Neill, T. Babeva, H. Awala, R. Retoux, S. Mintova, I. Naydenova
• A new photopolymer nano composite based on a low toxicity monomer and BEA type zeolite nano particles is developed.
• Significant improvement of the refractive index modulation in holographic recording.
• Nanoparticles’ pores remain empty – the nano composite is suitable for holographic sensors.
• The improved dynamic range – due to redistribution of the nano particles.
• Monomer and pore sizes – important factors in photopolymer nanocomposite design.
The effect of zeolite nanoparticles with BEA type framework structure on the optical properties of a diacetone acrylamide (DA)-based holographic photopolymer has been investigated. Both types of zeolite nanocrystals, as synthesized (BEA) and silver containing (BEA-Ag), are used for doping the DA photopolymer. Doping of the DA photopolymer with BEA zeolites results in an 11% decrease of the average refractive index of the nanocomposite layer, while the inclusion of BEA-Ag nanoparticles decreases the average refractive index by 3% only. This observation is in good agreement with the fact that the contrast in refractive index between the host photopolymer and nanoparticles is expected to be much lower for the BEA nanoparticles containing Ag in their pores. Doping of the DA photopolymer with pure BEA zeolite nanoparticles results in a significant increase in refractive index modulation due to holographic recording, Δn, of up to 91% at a concentration of 2 wt.% compared to un-doped layers. For the BEA-Ag zeolites, a maximum increase in Δn of up to 17% at a concentration of 0.5 wt.% is observed. The increase in Δn is attributed to the difference in n between the host photopolymer and nanoparticles and the redistribution of the nanoparticles during holographic recording. It is demonstrated that the DA photopolymer is compatible as a host material for the porous BEA nanoparticles. This is due to the large size of the DA monomer molecules, which restricts monomer migration into the zeolite pores and thus the pores of the Ag-free BEA nano particles remain empty, making them suitable for application in holographic sensors.