Synthesis,structural and electrical characterization of PbS NCs in titania sol–gel films

Nanocrystals of lead sulfide were grown in TiO₂ (titania) thin films prepared by a sol-gel process. The synthetic procedure as well as the structural, optical, and electrical properties of the films are demonstrated. The structures and morphology of PbS nanocrystals were analyzed using HRTEM, SAED, AFM, HRSEM, XRD and EDAX elemental analysis technique. When the concentration of PbS in the titania matrix is 20 mol%, PbS NCs with a diameter of 2.0 nm are created. At a higher PbS concentration (> 40 mole%) in the titania matrix, PbS NCs and PbS clusters are created not only within the TiO₂ film but also on the external surface of the TiO₂ film. By increasing the PbS concentration up to 50 mol%, PbS nanocrystals of 6–8 nm in diameter are formed within the titania film and PbS clusters with a base size of about 100 nm² and a height up to about 20 nm were self assembled on the external surface of TiO₂ film. Quantum size effect and band gap energies were obtained from shifts of the absorption edge. For electrical measurements, PbS–TiO₂ films were deposited on an ITO/glass substrate, and then covered with gold contact. The electrical properties of ITO/PbS NCs–TiO₂/Au and ITO/PbS NCs–TiO₂/PbS cluster/Au structures were studied. I–V characteristics of the one layer structure are nearly linear and symmetric, while those of the two-layer structure exhibit rectifying behavior.     

Optical and Conductivity Properties of PbS Nanocrystals in Amorphous Zirconia Sol-Gel Films

Lead sulfide (PbS) nanocrystals (NCs), embedded in amorphous zirconia sol-gel film with different PbS mole concentration (5–30%), were grown at temperature, ranging from 200°C to 350°C. The size of PbS NCs was determined by TEM and by blue shift of the absorption edge. The size increased with an increase of the synthesis temperature and PbS mole concentration. The optical and electrical properties of various sizes of PbS NCs in zirconia film are investigated utilizing absorption, photoluminescence (PL) and current-voltage measurement. The PL spectra were Stokes shifted from the corresponding absorption edge by about 0.5 eV. The latter can be associated with recombination process from surface state. The electrical properties were investigated by the deposition of the PbS NCs-zirconia films on ITO/glass substrate, followed by their coverage with gold contact. The current-voltage characteristics depend on the PbS NCs size and exhibits nonlinear nearly symmetric curve, associated with the space-charge limited current or the tunneling of carriers through the nanocrystalline film.     

Blue laser dye spectroscopic properties in solgel inorganic-organic hybrid films

A blue solid-state laser material based on 4,4' dibenzyl carbamido stilbene-2,2' disulfonic acid incorporated into solgel zirconia and inorganic-organic hybrid matrices is presented. The absorption maxima of the dye in various matrices are around 339-361 nm, and the broad fluorescence peaks are at 411-413 nm. Optical gain measurements using the variable stripe method show amplified spontaneous emission peaking at 437 nm.