Recently,
the two-dimensional (2D) elemental material tellurium
(Te) has drawn considerable attention, since it possesses high transport
properties, wide broadband absorption, excellent thermoelectric properties,
and prominent air stability. However, the anisotropic properties and
carrier dynamics of this material are less stated. Here, Te nanoflakes
are prepared by the hydrothermal method. Highly anisotropic properties
are illustrated by polarized Raman spectra and transient absorption
spectroscopic measurements as well as density functional theory (DFT)
calculations. Photocarrier dynamincs are probed by temporally resolved
transient measurements with an exciton lifetime of 25 ps. These results
imply that Te can be treated as a competitive material for further
anisotropic devices and applications.
Energy transfer of a van der Waals heterostructure formed by monolayers of WSe2 and PtSe2 is studied by steady-state photoluminescence and time-resolved transient absorption spectroscopy. The heterostructure sample is fabricated by transferring a mechanically exfoliated WSe2 monolayer onto a PtSe2 monolayer film obtained by chemical vapor deposition. The sample is thermally annealed to improve the interface quality. Photoluminescence of the heterostructure is quenched by 4 times compared to the individual WSe2 monolayer, indicating excitation transfer from WSe2 to PtSe2 . Femtosecond transient absorption measurements with two configurations show that both the electrons and the holes can transfer from WSe2 to PtSe2 on a sub-picosecond time scale, while neither can transfer from PtSe2 to WSe2. These results indicate that WSe2 and PtSe2 monolayers form a type-I band alignment with both the conduction band minimum and the valence band maximum in the PtSe2 layer.
Color-tunable electroluminescence (EL) from a single emitting material can be used to develop single-pixel multicolor displays. However, finding materials capable of broad EL color tuning remains challenging. Herein, we report the observation of broad voltage-tunable EL in colloidal type-II InP/ ZnS quantum-dot-seeded CdS tetrapod (TP) LEDs. The EL color can be tuned from red to bluish white by varying the red and blue emission intensities from type-II interfaces and arms, respectively. The capacitor device proves that an external electric field can enhance the color tuning in type-II TPs. COMSOL simulations, numerical calculations, and transient absorption measurements are performed to understand the underlying photophysical mechanism. Our results indicate that the reduced hole relaxation rate from the arm to the quantum dot core can enhance the emission from the CdS arms, which is favorable for EL color tuning. This study provides a novel method to realize voltage-tunable EL colors with potential in display and micro-optoelectronic applications.
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