Lanthanide-doped down-conversion fluorides: synthesis, characterization, and applications

摘要

Down-conversion phosphors based on ions of lanthanides can be used to convert UV/blue components of solar spectrum in near-infrared radiation more suitable for conventional silicon photovoltaic (PV) cells. Comparing to other down-convertors, their advantages are long Stokes shift (> 300 nm) excluding re-absorption, and environment safety. However, down-conversion efficiency remains an issue. The paper reports on synthesis and characterization of down-conversion phosphor based on lanthanide-doped fluoride NaYF_4:Yb~(3+), Er~(3+). The phosphor was synthesized using inexpensive wet method and further baked at ~500°C for 1 h to convert NaYF_4 matrix from cubic to hexagonal phase. The obtained micro-powder was ball-milled to nano-powder. The phosphor demonstrated down-conversion radiation from 830 to 1100 nm attributed to Yb~(3+). The Stokes shift was ~ 600 nm. The intensity of NIR peak radiation increased three times with increasing concentration of Yb~(3+) from 3 to 14%. A thin-sheet down-convertor of a Luminescent Solar Concentrator (LSC) was made in the form of a projector Mylar transparency coated with nanocolloid of the phosphor in a solution of polymer PMMA in chlorobenzene. Such thin sheet improved by 15% the PV power produced by the LSC being illuminated with a solar simulator as compared to an incandescent light bulb. The obtained results can be used in building more efficient PV green power.