Ultraviolet saturable absorption and ultrafast carrier dynamics in ultrasmall black phosphorus quantum dots

Abstract

Understanding the photoexcited carrier-relaxation actions in ultrasmall black phosphorus quantum dots (BPQDs) will play a crucial role in the fields of electronics and optoelectronics. Herein, we report the ultraviolet (UV) saturable absorption and ultrafast photoexcited carrier-relaxation dynamics of BPQDs. The ultrasmall BPQDs are synthesized using a facile liquid-exfoliation method and possess a diameter of 3.8 ± 0.6 nm and a thickness of 1.5 ± 0.4 nm. Femtosecond open-aperture (OA) Z-scan measurements showed typical saturable absorption properties in the UV band. A negative nonlinear optical (NLO) absorption coefficient of -(1.4 ± 0.3) × 10 cm GW and a saturable intensity of 6.6 ± 1.3 GW cm were determined. Using a degenerate pump-probe technique, an ultrafast photoexcited carrier-recombination time was observed in the range of 216-305 fs, which was 3 orders of magnitude faster than that of BP nanosheets. Such an ultrafast relaxation component may be attributable to the edge- and step-mediated recombination and was confirmed by our density functional theory (DFT) calculations. This work provides fundamental insight into the underlying mechanism of the photoexcited carrier relaxation dynamic action in BPQDs which can enable UV photonic devices.

Black Phosphorus Quantum Dots Gated, Carbon‐Coated Fe3O4 Nanocapsules (BPQDs@ss‐Fe3O4@C) with Low Premature Release Could Enable Imaging‐Guided Cancer Combination Therapy

“…As illustrated in Figure S5A, liquid exfoliation involves ultrasound probe sonication followed by ice‐bath sonication of bulk BP powder in 1‐methyl‐2‐pyrrolidone (NMP). The ultra‐small BPQDs obtained by centrifugation is dispersed in water, and polylysine (PL) is conjugated to enhance their stability in the physiological medium . TEM was applied to obverse the morphology and size distribution of the synthesized BPQDs.…”

“…[33] As illustrated in Figure S5A, liquid exfoliation involves ultrasound probe sonicationf ollowed by ice-baths onicationo f bulk BP powder in 1-methyl-2-pyrrolidone (NMP).T he ultrasmall BPQDs obtained by centrifugation is dispersed in water, and polylysine (PL) is conjugated to enhancet heir stabilityi n the physiological medium. [34] TEM was applied to obverse the morphology and size distribution of the synthesized BPQDs. Figure 1E showst he BPQDsa re irregular in shape, while the histograms hows the size distribution taken from over 80 nanoparticles and the average size of 1.8(AE 0.9) nm.…”

Novel two-dimensional monoelemental and ternary materials: growth, physics and application

“…The 2D BP nanosheets have been demonstrated to exhibit unique physical and optoelectronic properties including the quantum Hall effect, saturable absorption and high performance of transistors and infrared PDs [55][56][57]. Subsequently, focus has been on the monolayer and fewlayer monoelemental 2D materials of group-VA elements (As, Sb, Bi, Te and Se), showing the promising candidates in future applications in electrics and optics [58].…”

Fluorination‐Enhanced Ambient Stability and Electronic Tolerance of Black Phosphorus Quantum Dots

“…Given their novel optical and electronic properties, 2D material‐derived QDs have widespread applications in bioimaging,7 photodynamic therapy,8 photo‐/electrocatalysis,9 photodetection,10 and sensing 11. Black phosphorus QDs (BPQDs) or phosphorene QDs possess unique features, such as broadband absorption5, 13 and photoluminescence in the violet–green14 and near‐infrared (NIR)15 regions, owing to the special washboard‐like layered structure combined with the tunable bandgap (0.3–2.0 eV) of phosphorene 12. However, BPQDs are subjected to environmental degradation, similar to that of phosphorene 16.…”