The Second Order Nonlinear Susceptibility of Quantum Confined Semiconductors—A Single Dot Study

Detection of the second harmonic generation from single CdTe quantum dots of ∼11.5 nm diameter enables us to obtain an absolute value for the nonlinear susceptibility χ (2) of these nanoparticles as well as their dispersion properties. These measurements, complemented by ensemble hyper-Rayleigh scattering characterization, elucidate the role of quantum confinement in the second harmonic generation process. We show that, under similar excitation conditions, the χ (2) of quantum dots can significantly exceed that of the corresponding bulk material. The results indicate that by careful choice of excitation wavelength and material, kilo-counts per second rates of second harmonic generation photons can be obtained from quantum dots with <10 nm diameters, making second harmonic scattering quantum dots a promising option for use as biolabels.