Lighting products consume about 20% of total electric power, so the lighting industry should take a large responsibility for energy saving. Fluorescent lamps are a particularly critical light source for energy saving because they are widely used. Although the fluorescent lamp has high efficiency, its energy-transition rate is still as low as 25%. There is thus much room for improvement.
The key issue for efficiency improvement is the phosphor technology. Phosphors have been researched and improved based on the one-photon emission theory. Currently, the highest phosphor efficiency (transition rate of UV to visible) is over 40%. However, the energy of 254nm UV photon of Hg discharge is 4.9eV, which could be transferred to two visible photons.
We investigated the feasibility of the two-photon approach. We specifically studied a phosphor with an activator of a metal atom in an atomic state, which produces atomic-like emissions from an isolated metal atom fixed in a matrix. First, we theoretically studied the selection of possible metal atoms and analized the probability of two-photon emission. We searched for a method for fixing and isolating atoms in a matrix at room temperature and analyzed the energy shift of an excited atoms. As a result, we could have a prospect of the feasibility. Next, we conducted an experiment to fabricate a new phosphor sample by fixing an atom in an atomic state in a matrix and evaluatedthe performance of the samples. We selected Fe atoms, an amorphous silica as a matrix, and sol-gel fabrication method.
We found that Fe atoms on a silica matrix were fixed in an atomic state by sol-gelfabrication and emitted fluorescent light at lower atomic densities. However, the emission was not made by the visibletwo-photon transition, but by continuous deep-blue continuos emission.
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