Abstract of Publication No. 598
J. J. Eilers, D. Biner, J. T. van Wijngaarden, K. Krämer, H.-U. Güdel and A. Meijerink
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.