The optical properties of Auramine O (AuO) inside AOT/Water/n-Decane nano-droplet were studied using UV–vis, fluorescence, Raman and photon correlation spectroscopy techniques. The effect of nano-droplet size and concentration on the fluorescence redshift of AuO and hence the ratio of the dipole moment of the excited state to the ground state (μe/μg) was investigated. The AuO nano-droplets were prepared by mixturing AuO in AOT/Water/n-Decane microemulsion, with different nano-droplet concentration and two different nano-droplet size. The results indicated that at the same AuO concentration the fluorescence intensity depends on size of droplet and droplet concentration that it is due to the change of μe/μg by formation of microemulsion. It was observed that the fluorescence intensity have inverse relationship with size of droplet and directly related to the droplet interaction. Also, the photon correlation spectroscopy of the prepared samples showed the attractive interaction between the nano-droplets increase with the increase of AuO in nano-droplets that it can affect on dipole moment and fluorescence spectra of AuO.

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