Red-emitting Ca 1−x Sr x S:Eu 2+ Phosphors as Light Converters for Plant-growth Applications

A series of Ca 1−x Sr x S:Eu 2+ y mol% phosphors were synthesized with solid state reactions and with various Ca/Sr ratio and Eu 2+ doping concentrations. The influences of the lattice composition and the Eu 2+ doping level on photoluminescent properties were analyzed. With doping concentrations between 0.1 to 3 mol%, concentration quenching takes place leading to the decrease of luminance; the emission maxima are also red-shifted. Further, this work reports enhanced photosynthetic activities of intact spinach leaves due to spectral modification of simulated solar irradiation by one synthesized phosphor (Ca 0.4 Sr 0.6 S:Eu 1 mol% ). The CO 2 assimilation rates of intact spinach leaves were monitored with an effective homemade photosynthesis measurement system with controlled light conditions. The phosphor could efficiently convert the photosynthetically less active green part of the solar spectrum into the red, with a broad-band red emission centered at 650 nm and a halfband-width of 68 nm, giving an excellent match with the absorption spectrum of spinach chloroplasts. By careful referencing the photon flux, we found an enhanced photosynthetic activities by about 30 % due to the emission of the phosphor.