Excitonic Transitions and Off-resonant Optical Limiting in CdS Quantum Dots Stabilized in a Synthetic Glue Matrix

Abstract

Stable films containing CdS quantum dots of mean size 3.4 nm embedded in a solid host matrix are prepared using a room temperature chemical route of synthesis. CdS/synthetic glue nanocomposites are characterized using high resolution transmission electron microscopy, infrared spectroscopy, differential scanning calorimetry and thermogravimetric analysis. Significant blue shift from the bulk absorption edge is observed in optical absorption as well as photoacoustic spectra indicating strong quantum confinement. The exciton transitions are better resolved in photoacoustic spectroscopy compared to optical absorption spectroscopy. We assign the first four bands observed in photoacoustic spectroscopy to 1se–1sh, 1pe–1ph, 1de–1dhand 2pe–2phtransitions using a non interacting particle model. Nonlinear absorption studies are done using z-scan technique with nanosecond pulses in the off resonant regime. The origin of optical limiting is predominantly two photon absorption mechanism.

Two-photon absorption and optical limiting in tristhiourea cadmium sulphate

“…From repeated measurements it is estimated that the b values lie within an error bar of ±10%. In comparison, under similar excitation conditions, Bi nanorods [17] gave a b value of 10 À11 m/W, Cu nanocomposite glasses [18] were between 10 À12 and 10 À10 m/W, Au-Ag core-shell nanoparticles [19] were between 10 À10 and 10 À9 m/W, and CdS quantum dots [20] were at 10 À9 m/W. In the case of metal-organic coordination complexes, the organic ligand is usually more dominant regarding the NLO effect.…”

Third-order nonlinear optical response of Ag–CdSe/PVA hybrid nanocomposite

“…It is a direct band gap material with E g = 1.74 eV at 300 K [7] and exhibits quantum confinement at larger size as compared to CdS nanoparticles due to its large exciton Bohr radius (CdSe * 5.6 nm, CdS * 3 nm) [8,9]. The modern optical information technology requires materials with large optical nonlinearity and fast response times.…”

Synthesis and nonlinear optical characterization of new 1,3,4-oxadiazoles

“…Therefore β will have contributions from genuine TPA as well as ESA effects. Under similar excitation conditions, NLO materials like Cu nanocomposite glasses gave β values of 10 -10 -10 -12 m/W (Karthikeyan et al 2008), bismuth nanorods gave 5⋅3 × 10 -11 m/W (Sivaramakrishnan et al 2007) and CdS quantum dots gave 1⋅9 × 10 -9 m/W (Kurian et al 2007) respectively. These values show that the present samples have an optical nonlinearity comparable to these recently investigated nanomaterials.…”