Induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical nanocrystal processes

The second harmonic generation (SHG) is one of the measures of the optical nonlinearity. However, the SHG is prevented by symmetry in a centrosymmetric material. Therefore, in order to observe the SHG it is necessary to form a noncentrosymmetric process in a centrosymmetric material. Noncentrosymmetric nanosize-material processes CdI2 are formed by doping it with the impurity copper, controlling the size of the crystal and crystal temperature, and by pumping with an IR laser beam. The noncentrosymmetricity in the processes are probed by the observation of SHG and the second-order optical susceptibility ( χijk(2) χijk(2) ) is calculated from the SHG data. The value of χijk(2) χijk(2) is found to depend fashionably on the impurity content of the nanomaterials: χijk(2) = C1 exp[-1∕2{(Si-C2)∕C3}2] χijk(2)=C1 exp[-1∕2{(Si-C2)∕C3}2] , where Si is the concentration of impurity of the type i (here Si is SCu), and C1, C2 and C3 are parameters whose values depend on the crystal temperature and thickness of the nanomaterials. A photoluminescence measurement supports the third-order nonlinearity ( χijkl(3) χijkl(3) ) of the centrosymmetric CdI2 system and hence SHG in the induced processes. The results also show that a significant enhancement (from 0.37 pm/V to 0.83 pm/V) in the noncentrosymmetric response χijk(2) χijk(2) is achieved in nanomaterials with reduced sizes and at low temperatures. A recipe of the induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical processes CdI2 is explored and the results are discussed. However, the findings resulting from this investigation show that cadmium iodide nanocrystals might have potential in applications as optoelectronic nanodevices