Structure And Properties Of Holographic Polymer Composites With Liquid Crystals And Rod-Like Upconversion Nanocrystals

Holographic polymer/liquid crystal composites(HPLCs),in the form of periodically distributed polymer rich phase and liquid crystal rich phase,are one type of holographic recording materials formed through in-situ photopolymerization induced phase separation when irradiated by laser interference patterns.HPLCs have attacted considerable attention not only because of their high holographic performance,but also due to their unique electro-optic response capabilities.Nano-filler doping is one effective method to improve the performance of HPLCs.Yet,it still remains challenging to afford added optical functions to the HPLCs through nano-filler doping.In addition,the effect of anisotropic nano-fillers on the performance of HPLCs remains unclear.To this end,rod-like upconversion nanocrystals(UCNRs)were doped into HPLCs and the UCNRs were mainly placed in the polymer rich phase,which gave rise to polymer/luquid crystal/UCNRs ternary holographic composites with simultaneously boosted holographic performance and upconversion emission.To start with,UCNRs in a similar dimension(length: ~100 nm,diameter: ~19 nm)were synthesized,and the effect of UCNRs content on the structure and properties of holographic composites was investigated.Well defined periodically ordered structures remained when increasing the UCNRs content up to 15 wt%.The UCNRs were found to be mainly located in the polymer rich phase and only a small amount of UCNRs remained in the liquid crystal rich phase,based on the scanning electron microscopy characterization and thermal gravimetric analysis.Due to the well-formed phase separation structure,the holographic compostes held a high holographic performance with a diffraction efficiency of 90%.In addition,when increasing the UCNRs content,the driving voltage of holographic composites decreased slightly,while the upconversion emission intensity was dramatically enhanced.Next,four kinds of UCNRs with different sizes were synthesized and adopted to modify the HPLCs,and the effects of UCNRs size on holographic composites were studied.Results showed that all four types of UCNRs mainly presented in the polymer rich phase.However,as the size of UCNRs increased,more UCNRs were placed in the liquid crystal rich phase,resulting in a decrease of holographic performance.Finally,holographic composites were prepared with three kinds of UCNRs in a similar dimension but different emission colors.Holographic images were also reconstructed in these holographic composites,which were readily visible under ambient light,electric switchable and viewing angle dependent.Interestingly,the UCNRs modified holographic composites presented different upconversion emission colors(e.g.,red,green and blue)under the 980 nm near-infrared light irradiation.