Synthesis and nonlinear optical characterization of SnO2 quantum dots

The present paper demonstrates the preparation and characterization of SnO2 semiconductor quantum dots. Extremely small ∼1.1 and ∼1.4 nm SnO2 samples were prepared by microwave assisted technique with a frequency of 2450 MHz. Based on XRD analysis, the phase, crystal structure and purity of the SnO2 samples are determined. UV–vis measurements showed that, for the both size of SnO2 samples, excitonic peaks are obtained at ∼238 and ∼245 nm corresponding to ∼1.1 nm (sample 1) and ∼1.4 nm (sample 2) sizes, respectively. STM analysis showed that, the quantum dots are spherical shaped and highly monodispersed. At first, the linear absorption coefficients for two different sizes of SnO2 quantum dots were measured by employing a CW He–Ne laser at 632.8 nm and were obtained about 1.385 and 4.175 cm−1, respectively. Furthermore, the nonlinear refractive index, n2, and nonlinear absorption coefficient, β, were measured using close and open aperture Z-scan respectively using the same laser. As quantum dots have strong absorption coefficient to obtain purely effective n2, we divided the closed aperture transmittance by the corresponding open aperture in the same incident beam intensity. The nonlinear refraction indices of these quantum dots were measured in order of 10−7 (cm2/W) with negative sign and the nonlinear absorption coefficients were obtained for both in order of 10−3 (cm/W) with positive sign.