title: Visible-to-infrared quantum cutting by phonon-assisted energy transfer in YPO4:Tm(3+), Yb(3+) phosphors.
abstract: Quantum cutting (QC) of one visible photon into two infrared ones has been reported for the lanthanide ion couple (Tm(3+), Yb(3+)) in a variety of host lattices. The mechanism responsible for QC was assumed to be a cooperative energy transfer (ET) process from Tm(3+) to two Yb(3+) ions, however, no solid evidence was presented. Herein we report visible-to-infrared QC for (Tm(3+), Yb(3+)) in YPO4 phosphors. The ET process from the excited (1)G4 level of Tm(3+) to Yb(3+) was investigated in detail by means of optical spectroscopy. By monitoring the steady-state photoluminescence (PL) and PL decay of the intermediate (3)F4 level of Tm(3+) as a function of the Yb(3+) concentration, we demonstrated the QC of one incident blue photon into one near-infrared emitting photon at 1004 nm from Yb(3+) and simultaneously into one mid-infrared emitting photon at 1791 nm from Tm(3+), rather than two emitting photons from Yb(3+). It was revealed that such visible-to-infrared QC was induced by phonon-assisted ET instead of cooperative ET as previously reported. This kind of QC phosphors may have potential as solar spectral converters to enhance the external quantum efficiency in multi-junction solar cells based on narrow band-gap semiconductors such as Ge, PbS or In1-xGaxN.
authors.affiliation: Key Laboratory of Optoelectronic Materials Chemistry and Physics, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. xchen@fjirsm.ac.cn.
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.forename: Haomiao
authors.initials: H
authors.lastname: Zhu
authors.forename: Renfu
authors.initials: R
authors.lastname: Li
authors.forename: Datao
authors.initials: D
authors.lastname: Tu
authors.forename: Yongsheng
authors.initials: Y
authors.lastname: Liu
authors.forename: Wenqin
authors.initials: W
authors.lastname: Luo
authors.forename: Xueyuan
authors.initials: X
authors.lastname: Chen