Efficient visible to infrared quantum cutting through downconversion with the Er3+–Yb3+ couple in Cs3Y2Br9

Abstract

Downconversion of one visible photon to two near-infrared photons may increase the efficiency of c-Si solar cells by 30%. The lanthanide ion couple Er3+–Yb3+ is well known for efficient upconversion but for the reverse process, downconversion, fast multiphonon relaxation from the 4F7/2 level has been shown to compete with downconversion. Here we report efficient downconversion for the Er–Yb couple in Cs3Y2Br9. The low phonon energy in this bromide host suppresses multiphonon relaxation and efficient two step energy transfer from the 4F7/2 level of Er3+ is observed and results in strong 1000 nm emission from Yb3+. Based on emission spectra and luminescence life time measurements an intrinsic downconversion efficiency close to 200% is determined