Potassium dichromate (KD) is a common inorganic pigment used as a photosensitizer (PS) for photodynamic therapy (PDT). Numerous works in this area have so far reflected on organic dye and its colloidal system with linear absorption in PDT, while a few studies have been completed on potentials of nonlinear absorption (NLA) of inorganic KD for this type of treatment. Therefore, absorbance, nuclear magnetic resonance (NMR), and nonlinear optical (NLO) properties of KD and its formulations were described in detail. The pigment was also found to be positioned within the inner part of the droplet prepared with water, oil, and surfactant. The impact associated with the length of hydrocarbon-chain of anionic surfactant micelles and reverse micelles (RMs) on the NLO properties of KD was further investigated. The results revealed that the pigment had more interactions with the micelles prepared with a small-length-scale surfactant. The NLA and the second-order hyper-polarizabilities of KD were correspondingly proportional to the size of the RMs in an inverse manner. Moreover, encapsulation of the pigment in the RMs led to a reduction in the aggregation of the pigment and subsequently increased their NLA. Quantum calculations have been done to achive optimized geometry, dipole moment and band gap of KD and dimer of KD (2KD). It was demonstrated that using KD in a smaller size of RMs as PSs along with NLA via laser irradiation (LI) could be a very efficient method for treatment of Staphylococcus aureus (S.aureus).

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