jp5b00882_si_001.pdf (632.89 kB)
Understanding Energy Transfer Mechanisms for Tunable Emission of Yb3+-Er3+ Codoped GdF3 Nanoparticles: Concentration-Dependent Luminescence by Near-Infrared and Violet Excitation
journal contribution
posted on 2015-03-26, 00:00 authored by Dekang Xu, Chufeng Liu, Jiawei Yan, Shenghong Yang, Yueli ZhangEnergy transfer (ET) is an important
route to manage the population
density of excited states, giving rise to spectrally tunable emission
that is valuable for multicolor imaging and biological tracking. In
this paper, a case study of GdF3 nanoparticles (NPs) codoped
with Yb3+ and Er3+ was used to experimentally
and theoretically investigate the ET mechanisms under near-infrared
and violet excitation. Red-to-green ratio (RGR) is used as a primary
evaluating protocol, and the power-dependent luminescence and Er3+ 4I13/2 luminescence behavior are used
to identify the corresponding conjectures about ET mechanisms. Compared
with the four common upconversion (UC) models, a joint effect of energy-back-transfer,
multiphonon relaxation, and linear decay depletion mechanisms for
the Er3+ 4I13/2 manifold was proposed
for the UC process based on UC spectra for samples with different
dopant concentrations. Meanwhile, the varying RGR could also be observed
from downshifting (DS) emission spectra. The ET mechanism for the
DS process, where three cross-relaxation processes coexisted including
the Yb3+ 2F5/2 manifold as energy
in-transit state, was proposed for the first time. The findings are
expected to provide an approach for understanding ET mechanisms in
many Yb3+/Er3+ codoped UC and DS systems and
enable spectrally tunable emission properties for applications that
require precisely defined optical transitions.