Gold particles smaller than 2 nm in diameter were grown in glass. Their optical absorption spectrum did not show the usual plasma absorption band for gold particles; this band was spread by the small particle size. The absorption spectrum was calculated from the bulk optical properties of gold, modified for the small particle size; there was good agreement between calculated and measured spectra. The smallest particles containing from 20 to 40 gold atoms showed a λ−4 dependence of absorption on wavelength λ. This result implies that the absorption in these particles was entirely from free electrons at wavelengths above 0.3 μm.

No abstract

A detailed examination by transmission electron microscopy and selected−area diffraction revealed that the thin−film intergranular phase in a highly non−Ohmic multicomponent metal oxide varistor system based on ZnO with small additions of antimony, bismuth, cobalt, manganese, and tin oxides is amorphous and is chemically related to a Bi2O3−rich pyrochlore coexisting in the ceramic.

Glasses containing semiconductor particles coated with metal were synthesized and studied. Glasses containing CdS and silver were heated to grow the CdS particles first, followed by the growth of metal on them. The solubility of silver in the CdS glass was increased by changing the base glass composition. Optical absorption and transmission electron microscopy results showed that silver coated the CdS particles in these glasses. The CdS particles had to be a critical size before silver grew on them. This critical size was calculated from nucleation theory and was found to be in good agreement with the experimental results. Glasses containing CuCl particles were partially reduced in hydrogen to obtain copper-coated CuCl particles. Absorption spectroscopy and TEM indicated a copper coating on the particles.

We have found that traps can dominate important relaxation processes in PbS nanoparticles prepared by precipitation in borosilicate glass. The primary photoluminescence peak energy falls about 50 meV below the lowest absorption peak energy and has a long decay time of ∼4 μs. Photoinduced bleaching of the lowest absorption peak also has a long decay lifetime of ∼2 μs. Photoinduced bleaching also exhibits a surprisingly long rise time of hundreds of nanoseconds. Such long-lifetime effects must be attributed to multiple traps.

We have fabricated PbS particles in glass of average size from 1.2 nm to 3 nm. This allows us to tune the energy of the lowest electron-hole pair transition from 1.7 eV to 0.8 eV respectively. Optical absorption spectra show a pronounced quantum peak, implying a narrow size distribution. We have performed pump-probe spectroscopy where the probe is cw and the pump is nanosecond; this allows us to investigate a wide time scale. We have observed bleaching of the lowest quantum peak with lifetimes of ∼2 microseconds. We interpret this in terms of trapped carriers. Phenomenological description of observed effect is also presented.

Optical absorption of nanosized particles in glass was measured. The plasma absorption band was completely spread out for particles below about 1.5 ran in diameter, as also has been found by gold particles in water and a polymer. The growth kinetics suggested growth of spherical particles controlled by diffusion of gold from the matrix to the particles, and a constant number of growing particles, giving a narrow size distribution of particles. For particles below about one ran in diameter (31 gold atoms), the optical absorption was proportional to λ−4, as expected if the absorption results from free electrons in the particles.