Photophysical and nonlinear optical properties of carmine encapsulation compared with ionic solutions and environmental polarity

The nonlinear absorption coefficient (β) and nonlinear refractive index (n₂) of Carmine Encapsulation (CR-Cap) with H₂O/n-heptane/AOT solutions were investigated using a z-scan instrument. The transparent solution is made of water droplets containing carmine (CR), which are uniformly located in the continuous phase of n-heptane. The effects of Cetrimonium bromide (CTAB), NaCl, and NaOH on the β and n₂ values of CR in aqueous solution are studied and compared with CR-Cap. The values of β and n₂ for the CR-Cap have increased by 9 and 4.4 times, respectively, compared to those in its aqueous solution. The absorbance value and Rayleigh scattering (RS) change with environmental properties, while the optical gap is obtained as a constant 2.1 eV. The encapsulated CR has high RS and β values, which is caused by the increased polarizability of the molecule as a result of encapsulation, while aqueous solutions have low RS and β values. With quantum perturbation calculation, it is demonstrated that encapsulation increases the ground state dipole moment of CR compared to the aqueous solution. CR-Cap can be used as a photosensitizer in photodynamic therapy or optical devices.