*Green Synthesis of Metal Nanostructures and Its Nonlinear Optical Properties DOI: http://dx.doi.org/10.5772/intechopen.99449*

intensity in the presence of Ag. As the increase in the asymmetric ratio (<sup>5</sup> D0 ! <sup>7</sup> F2/ 5 D0 ! <sup>7</sup> F1), the decay rate of radiative transition increases than the decay rate of non-radiative transition of europium [50]. This shows that the presence of nanoparticles reduces the loss of energy due to non-radiative decay [51].

Similarly, the decay profile of the <sup>4</sup> G5/2 level samarium (1.45 μM) ions in the presence of silver NPs (2.32 μM) excited at 350 nm and monitoring 645 nm emission band as shown in **Figure 16(b)**. The decay is also single exponential with silver. Average decay τ values for samarium increases from 16 μs to 31 μs for 0 to 2.32 μM of silver and then reduces with an additional increase of silver. This behavior is due to enhancing in radiative decay rate. The samarium ions transmit energy to nanoparticles, then excited SPR converted into emission with enhancing luminescence efficiency consequently increase in lifetime. This is assigned to the luminescence emission intensity enhancing and quenching exhibited by samarium ions with silver. The lifetime of samarium ions is smaller as compared with europium ions may be because higher concentrations reduce the nonradiative decay rates.
