In a conventional p-n junction photovoltaic cell, made, for example, from silicon, the semiconductor assumes two roles at the same time: It harvests the incident sunlight and conducts the charge carriers produced under light excitation. In order to function at a good efficiency, the photons have to be absorbed close to the p-n interface. Electron-hole pairs produced away from the junction must diffuse to the p-n contact where the local electrostatic field separates the charges. To avoid charge carrier recombination during the diffusion, the concentration of defects in the solid must be small. This imposes severe requirements on the purity of the semiconductor material, rendering solid-state devices of the conventional type expensive.

We have developed a new molecular photovoltaic system for solar light harvesting and conversion to electricity. It is based on the spectral sensitization of a thin ceramic membrane by suitable transition-metal complexes. The film consists of nanometersize colloidal titanium dioxide particles sintered together to allow for charge carrier transport. When derivatized with a suitable chromophore, these membranes yield extraordinary efficiencies for the conversion of incident photons into electric current, exceeding 90% for certain transition metal complexes within the wavelength range of their absorption band. In this article, we discuss the underlying physical principles of these astonishing findings. Exploiting this discovery, we have developed a new type of photovoltaic device whose overall light-to-electric-energy conversion yield is 12–15% in diffuse day-light and 10% under direct (AM1.5) solar irradiation.

Recent breakthroughs in materials science and technology have led to improved dental restorative ceramics, metals, and resin-based composites. These breakthroughs have been most important since one of the major controversies during this period has centered on allegations of the physiological risks of mercury released from amalgam restorations. Dental amalgams have been used in the United States since 1832, yet not a single well-documented case of dental patient toxicity to mercury from amalgam restorations has been reported in the scientific literature.

A particularly extreme position has been adopted by the Swedish government, which has proposed the progressive elimination of amalgam as a dental restorative material by 1997. Among the materials that have been considered as the most biocompatible alternative to amalgam are dental ceramics. New ceramic products and technologies have gained considerable acceptance in Sweden even though their safety and efficacy have not been fully established.

Although dental ceramics constitute a much more costly alternative than some other materials, they offer the advantages of esthetics, inertness, durability, low thermal conductivity, and low diffusivity, as compared with amalgams. Although ceramics are generally considered to be inert in the oral cavity, there are certain phenomena associated with their use that may cause significant surface degradation of these materials and subsequent physiological side effects.