Spectroscopy is the study of interaction of electromagnetic radiation with matter. Optical spectroscopy is widely used in the characterization of nanostructured materials and can broadly be classified into two types: absorption and emission spectroscopy and the other is vibrational spectroscopy. Among these absorption and emission spectroscopy is used to determine the electronic structure of atoms, ions, molecules etc. The study of behavior of the electrons in the atoms or molecules exciting to a particular higher state from their ground state by the absorption of the photon of suitable energy is absorption spectroscopy. The electrons excited to the higher states are short lived and will de-excite to its initial state by different processes. Thus, the study of behavior of such electrons relaxing to the ground state is termed as emission spectroscopy.