Size dependent optical properties of quinacridonequinone nanoparticles prepared by liquid laser ablation in water

► We investigated size dependent optical properties of colloidal solutions. ► The colloidal solution of organic nano-particles was prepared by laser ablation. ► We found a linear correlation between absorption energy and particle diameter. ► The correlation provides us a simple method to estimate the diameter of nano-particles. ► The reason of the energy shift is considered to be due to surface effects.