With
the aim of realizing mid-temperature thermoelectric materials,
the electrical and thermal transport properties of the Zintl phase
compound BaCu2Te2 with a channel structure (Pnma) were systematically investigated. BaCu2Te2 exhibits moderate electrical transport properties
and low intrinsic thermal conductivity, which contribute to its high
thermoelectric figure of merit (zT = 0.72 at 823
K). The partial substitution of Cu with Ag led to a significant enhancement
of the Seebeck coefficient, as the carrier effective mass increased
from 1.0m
0 for BaCu2Te2 to 1.5m
0 for BaCu1.9Ag0.1Te2 at room temperature, and reduction
of the Hall carrier concentration. In addition, at higher temperature,
a lower thermal conductivity of ∼0.5 W m–1 K–1 was achieved for BaCu1.9Ag0.1Te2; this reduced thermal conductivity resulted
from the point-defect scattering arising from the Ag/Cu isovalent
substitution. Together, these integrated effects led to a significant
improvement of the quality factor β with a peak thermoelectric
figure of merit zT of 1.08 for BaCu1.9Ag0.1Te2 at 823 K. The average zT of BaCu1.9Ag0.1Te2 over the temperature
range of 323–823 K was 0.68, demonstrating its potential as
a promising thermoelectric Zintl compound in the mid-temperature range.
Without excess Li, anode-free Li-metal batteries (AFLMBs) have been proposed as the most likely solution to realizing highly-safe and cost-effective Limetal batteries. Nevertheless, short cyclic life puzzles conventional AFLMBs due to anodic dead Li accumulation with a local current concentration induced by irreversible electrolyte depletion, insufficient active Li reservoir and slow Li + transfer at the solid electrolyte interphase (SEI). Herein, SrI 2 is introduced into carbon paper (CP) current collector to effectively suppress dead Li through synergistic mechanisms including reversible I À /I 3 À redox reaction to reactivate dead Li, dielectric SEI surface with SrF 2 and LiF to prevent electrolyte decomposition and highly ionic conductive (3.488 mS cm À 1 ) inner layer of SEI with abundant LiI to enable efficient Li + transfer inside. With the SrI 2modified current collector, the NCM532/CP cell delivers unprecedented cyclic performances with a capacity of 129.2 mAh g À 1 after 200 cycles.
Lanthanide-doped
upconversion nanoparticles (UCNPs) as energy donors
for Förster resonance energy transfer (FRET) are promising
in biosensing, bioimaging, and therapeutic applications. However,
traditional FRET-based UC nanoprobes show low efficiency and poor
sensitivity because only partial activators in UCNPs possessing suitable
distance with energy acceptors (<10 nm) can activate the FRET process.
Herein, a novel excited-state energy distribution-modulated upconversion
nanostructure is explored for highly efficient FRET. Integration of
the optimal 4% Er3+ doped shell and 100% Yb3+ core achieves ∼4.5-fold UC enhancement compared with commonly
used NaYF4:20%Yb3+,2%Er3+ nanoparticles,
enabling maximum donation of excitation energy to an acceptor. The
spatial confinement strategy shortens significantly the energy-transfer
distance (∼4.5 nm) and thus demonstrates experimentally a 91.9%
FRET efficiency inside the neutral red (NR)-conjugated NaYbF4@NaYF4:20%Yb3+,4%Er3+ nanoprobe,
which greatly outperforms the NaYbF4@NaYF4:20%Yb3+,4%Er3+@SiO2@NR nanoprobe (27.7% efficiency).
Theoretical FRET efficiency calculation and in situ single-nanoparticle
FRET measurement further confirm the excellent energy-transfer behavior.
The well-designed nanoprobe shows a much lower detection limit of
0.6 ng/mL and higher sensitivity and is superior to the reported NO2
– probes. Our work provides a feasible strategy
to exploit highly efficient FRET-based luminescence nanoprobes for
ultrasensitive detection of analytes.
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