Microstructural and nonlinear optical properties of silica–titania sol-gel film doped with PbS quantum dots

Abstract

Thin silica–titania films doped with different concentration of PbS quantum dots (PbS/oxide molar ratios ranging from 5% to 25%) were fabricated via a sol-gel route. The structural properties were studied by x-ray diffraction, high-resolution transmission electron microscopy, and Rutherford backscattering spectrometry. The PbS crystals were found to have a mean diameter in the range 2.3–3.5 nm with narrow size distribution. The resonant nonlinear optical properties were studied by the nonlinear m-line technique and degenerate four-wave mixing. High negative nonlinear refractive indices (n2) were measured at 1.064 μm. Different n2 values were obtained for nanosecond excitation (n2=10−7–10−8 cm2/kW) and for picosecond excitation (n2=10−9–10−10 cm2/kW). The differences can be explained by saturation effects. Measurements at 532 nm showed n2 values ten times higher than at 1.064 μm. The response time of the nonlinearity for both wavelengths was below 35 ps.

Ultrafast Optical Nonlinearities in CdS Nanocrystalline Thin Films Prepared by Chemical Bath Deposition

“…3) at low excitation, and it saturates at higher intensities. From the diffraction efficiency the value of the third-order susceptibility jc 3 j can be computed [8]. We get jc 3 j % 6 Â 10 --16 m 2 V --2 .…”

Nonlinear Optical Zeolite Films for Second and Third Harmonic Generation

“…[28][29][30][31][32][33][34][35][36][37][38][39] However, their sensitivities have not yet reached the degree that is sufficient for practical applications. Zeolites are also excellent hosts for QDs [40][41][42][43][44][45][46][47][48][49][50][51] and have many advantages over glass and polymers due to the followings.…”

“…Preparation of Zeolite-Y Films on ITO Glass: Despite the fact that zeolites are excellent hosts for semiconductor QDs [28][29][30][31][32][33][34][35][36][37][38][39] and QDs have shown 3O-NLO properties, the measurements of 3O-NLO properties of zeolite-encapsulated QDs could not be made due to the difficulty to prepare zeolite films supported on optically transparent substrates such as glass and quartz with reasonably high binding strengths between the films and substrates. For instance, when zeolite-Y films are grown on ordinary glass or fused silica, they readily peel off the substrates during drying, ionexchange with other ions, and calcination to remove organic contaminants.…”

Microgranules and Nanoparticles on Their Surfaces

“…Such systems are commonly prepared by sol-gel processing. CdS and PbS nanoparticles prepared in aqueous solutions by known techniques can be introduced into silica sol so as to obtain SiO 2 microgranules each containing several nanoparticles [264][265][266]. Another way is to introduce Cd ions into sol and then heat-treat the resultant gel in an H 2 S atmosphere [267].…”