Hybrid electronic properties between the molecular and solid state limits: Lead sulfide and silver halide crystallites

Abstract

Tiny single PbS crystals of ∼25 Å diameter are synthesized and studied optically in low-temperature colloidal solutions. Electron microscopic examination shows a simple cubic rock salt structure with a lattice constant unchanged, within experimental error, from the bulk value. These crystallites lack the near infrared electronic absorption characteristic of bulk PbS. The small crystallite absorbance in the visible rises more steeply than does the bulk absorbance. These results reflect electron and hole localization if one considers the variation in effective mass across the band structure. A simple discussion of localization anywhere in the Brillouin zone is given. For the first time, crystallite syntheses are carried out in solvent mixtures that form transparent glasses upon cooling. The PbS spectra are independent of temperature (at current experimental resolution) down to 130 K, in contrast to earlier results for quantum size exciton peaks in ∼20 Å ZnS crystallites. Previously published observations of size dependence in the excited state electronic properties of AgI and AgBr are explained as consequences of electron and hole localization in the small crystallites. AgBr appears to be the first indirect gap semiconductor to be examined in the regime where bulk properties are not fully formed.

Nanocomposites of polymers and metals or semiconductors: Historical background and optical properties

“…As mentioned above, optical constants of nanoparticles can differ from those of the bulk material and in addition depend on the particle size [39][40][41][42][69][70][71][72][73][74][75][76] , which will be evident below with the example of the refractive index. However, the most striking demonstration of related phenomena is probably, as indicated in the preceding section, the color dependence of nanoparticles on the particle size.…”

“…4 91) ) renders this compound attractive for model experiments on the refractive index of polymer nanocomposites. The synthesis of PbS nanoparticles proceeds without problems, and there are many reports on colloidal PbS in dilute solutions 69,70,76,[92][93][94][95] . Nanocomposites containing PbS have also been described.…”

Structural, optical and magnetic studies on non-aqueous synthesized CdS:Mn nanomaterials

“…By controlling and maneuvering the materials under nanoregime, new pathways are opened to the development of device technologies. Recently Sakthi Sudar Saravanan et al have reported the nanodimensional materials show appreciable quantum confinement effects upon the lowering size of the materials [1][2][3][4][5].…”

“…In order to achieve the listed advantages from CdS:Mn system, we have chosen the wet chemical precipitation method. Brus et al (1983) [1,2] have reported that the optical absorption behavior of semiconductor nanomaterials are the function of quantum confinement effect. Size dependent optical absorption nature of semiconductor nanosystems strongly follows the confinement theory, which predicts that the effective mass approximation gives suitable solution for weak confinement range (particle radius higher than the Bohr radius).…”

Solution Synthesis of Germanium Nanowires Using a Ge2+ Alkoxide Precursor

“…6-10 Nanoscale Ge 0 semiconductor systems are superior to Si 0 for (i) higher electron and hole mobility, 11 (ii) a larger Bohr exciton radius that yields a more pronounced quantum confinement effect, 12,13-15 and (iii) a predicted nanostructure with direct-bandgap behavior, although bulk Ge 0 is an indirect bandgap material. 16 One reason for the scarce exploration of Ge 0 nanowires as an advanced material is due to the lack of a simple and benign synthetic pathway to this morphology. 17 The previously reported routes cover a myriad of processes, including chemical vapor deposition (CVD), 6, 18 laser ablation, 19 vapor-liquid-solid (VLS) growth, 20 templated supercritical fluid, 21-24 and combination of these techniques.…”