Improvement of optical properties and memory effect in ferroelectric liquid crystal by incorporating core/shell CoFe₂O₄/ZnO nanocrystals

Here, we report incorporation of spinel ferrite CoFe₂O₄/ZnO (ZCOF) core/shell nanocrystals (NCs) in ferroelectric liquid crystals (FLC) resulting better optical properties. The optical properties of FLC were studied using polarizing optical microscopy (POM) and photoluminescence (PL) measurements. The POM texture analysis reveals improved molecular alignment of FLC by presence of ZCOF NCs. PL emission peak show about 1.4 times improvement of area under curve ratio as a result of enhanced FLC molecular ordering. The improved emission properties of FLC were result of reduced defect state emissions by presence of ZCOF NCs. The optical memory in FLC (20 s) as well as in ZCOF-incorporated FLC (2 min) is also reported using POM texture analysis with aid of ImageJ software. Memory measurements reveal winding and unwinding of helix of FLC by external electric field takes place with discrete steps as a result of smectic subphases emergence. Study of applying staircase potential to FLC material shows critical electric field of helix unwinding is 1 kV/cm. In summary, presence of ZCOF NCs in FLC would give better contrast, better brightness, and optical memory which might be useful for future FLC-based display and electronic devices.