Induction strategies of the noncentrosymmetricity in centrosymmetric nonlinear optical nanocrystal processes

Abstract

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 (χ_ijk⁽²⁾) is calculated from the SHG data. The value of χ_ijk⁽²⁾ is found to depend fashionably on the impurity content of the nanomaterials: χ_ijk⁽²⁾ = C₁ exp[-1∕2{(S_i-C₂)∕C₃}²], where S_i is the concentration of impurity of the type i (here S_i is S_Cu), 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 (χ_ijkl⁽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 χ_ijk⁽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.

Graphical abstract