A new kind of light-generation mechanism: Incandescent radiation from clusters

A novel technique to generate hot refractory metal clusters is explained. A regenerative chemical cycle is used to form small clusters inside a microwave-excited high-pressure discharge which heats the clusters to 4700 K (rhenium) or 3800 K (tungsten). The discharge’s emission spectrum exhibits a strong continuum, which is the incandescent radiation of clusters. The spectral shapes of the continua and the positions of their maxima (Re: 550 nm; W: 700 nm) are characteristic of the refractory metal. A first theoretical description of the clusters’ radiation can be based on the Mie theory. Measurements of emission and absorption coefficients are performed to determine the optical properties and temperatures of the clusters. The existence of clusters with an average size of about 2.5 nm is proved by a laser scattering experiment. The properties of the cluster radiation, especially the continuous spectrum and the high luminous efficiency, are attractive for lighting applications.