Characterization of Infrared-Active Fluorescent Concentrators

Fluorescent concentrators are able to concentrate direct and diffuse radiation. Most available materials for fluorescent collectors utilize only the visible part of the solar spectrum which results in low overall efficiencies of fluorescent concentrator systems. In this paper, we investigated Nd3+-doped barium borate glass as a promising candidate for fluorescent concentrators. Nd3+ is active in the infrared. Samples with different Nd3+ concentrations were investigated by recording absorption and photoluminescence spectra. The spectral collection efficiency was determined by optical measurements. An efficiency of 9.6 % was found at wavelengths of 527 nm and 579 nm, respectively, for a sample doped with 1 mol% Nd. In the range of 800 nm, efficiencies of around 6 % were achieved. Additionally, a silicon solar cell was attached to the edge of each of the investigated collector samples and the external quantum efficiency (EQE) of these fluorescent concentrator systems was measured. A comparison of the shapes of the optically determined spectral collection efficiency and the EQE suggests that the dominant light guiding mechanism depends on the Nd concentration.