ABSTRACT
Optical modulation of high-harmonics generation in solids enables the detection of material properties, such as the band structure, and promising new applications, such as super-resolution imaging in semiconductors. Various recent studies have shown optical modulation of high-harmonics generation in solids, in particular, suppression of high-harmonics generation has been observed by synchronized or delayed multipulse sequences. Here we provide an overview of the underlying mechanisms attributed to this suppression and provide a perspective on the challenges and opportunities regarding these mechanisms. All-optical control of high-harmonic generation allows for femtosecond, and in the future possibly subfemtosecond, switching, which has numerous possible applications: These range from super-resolution microscopy to nanoscale controlled chemistry and highly tunable nonlinear light sources.
ABSTRACT
Deciphering and modulating the carrier dynamics of perovskite nanocrystals (Pe-NCs) is crucial for their optoelectronic applications, which remains elusive to date. Herein, we, for the first time, explore the ultrafast dynamics of perovskite core-shell type NCs using CsPbBr3@ZnS as a model system. According to the transient spectroscopic characterization, a physical picture of the ultrafast dynamics in core-shell Pe-NCs is built. Specifically, we directly observed the "hot" hole transfer from CsPbBr3 to ZnS and confirmed the formation of charge-transfer state in CsPbBr3@ZnS NCs. Such ultrafast (<100 fs) hole rearrangement speeds up the carrier cooling and breaks the hot phonon bottleneck effect in Pe-NCs. Moreover, thanks to the charge separation in CsPbBr3@ZnS NCs, the Auger recombination is largely suppressed and the Auger lifetime is increased nearly 5-fold compared to that of "pure" CsPbBr3 NCs, which endows CsPbBr3@ZnS NCs with unique optical gain properties. These results are informative for halide perovskite-based applications, such as photocatalysis, hot-carrier photovoltaics and lasers.
ABSTRACT
Due to strong Coulomb interactions, two-dimensional (2D) semiconductors can support excitons with large binding energies and complex many-particle states. Their strong light-matter coupling and emerging excitonic phenomena make them potential candidates for next-generation optoelectronic and valleytronic devices. The relaxation dynamics of optically excited states are a key ingredient of excitonic physics and directly impact the quantum efficiency and operating bandwidth of most photonic devices. Here, we summarize recent efforts in probing and modulating the photocarrier relaxation dynamics in 2D semiconductors. We classify these results according to the relaxation pathways or mechanisms they are associated with. The approaches discussed include both tailoring sample properties, such as the defect distribution and band structure, and applying external stimuli such as electric fields and mechanical strain. Particular emphasis is placed on discussing how the unique features of 2D semiconductors, including enhanced Coulomb interactions, sensitivity to the surrounding environment, flexible van der Waals (vdW) heterostructure construction, and non-degenerate valley/spin index of 2D transition metal dichalcogenides (TMDs), manifest themselves during photocarrier relaxation and how they can be manipulated. The extensive physical mechanisms that can be used to modulate photocarrier relaxation dynamics are instrumental for understanding and utilizing excitonic states in 2D semiconductors.
ABSTRACT
Slow hot carrier (HC) cooling resulting from hot phonon bottleneck has been widely demonstrated in metal halide perovskites. Although manipulating HC kinetics in these materials is of both fundamental and technological importance, this task remains a daunting challenge. Here, via interfacial engineering, i.e., epitaxial growth of Cs4PbBr6 on CsPbBr3 nanocrystals (NCs), we have revealed an obvious shortening of HC cooling times, evidenced by transient absorption and ultrafast PL spectra. Collaborated with the longitudinal optical (LO) phonon model, theoretical calculations verify the breaking of the hot phonon bottleneck in CsPbBr3@Cs4PbBr6 and identify the interfacial electron-LO phonon coupling as the leading mechanism for the observed large tuning of HC cooling times. Especially, the participation of LO phonons from Cs4PbBr6 enables the efficient Klemens channel for hot phonon decay. Our findings establish an effective method to tailor HC dynamics in perovskite NCs, which could be conducive to improving the performance of optoelectronic applications.
ABSTRACT
Despite intensive research on ion migration (IM) in organic-inorganic hybrid metal halide perovskites, much less is known about the irradiation effect on IM in all-inorganic perovskites, especially for those single crystals lacking complicated grain boundaries. Herein, the real-time IM process and the corresponding photoluminescence (PL) spectra induced by laser irradiation in all-inorganic CsPbBr x I(3-x) single crystals prepared by chemical vapor deposition (CVD) were investigated. We proposed that a local electric field acts as a driving force for IM and confirmed this by applying a bias to an indium tin oxide (ITO)/perovskite/ITO configuration. According to the control experiments on CsPbBr x I(3-x) micro-platelets with and without polymethyl methacrylate (PMMA) coating, it is concluded that the vacancy defect on the single crystal surface is the main pathway for IM. Our work is important for understanding and controlling light induced IM in all-inorganic perovskites.
ABSTRACT
Graphene has been widely investigated for use in high-performance photodetectors due to its broad absorption band and high carrier mobility. While exhibiting remarkably strong absorption in the ultraviolet range, the fabrication of a large-scale integrable, graphene-based ultraviolet photodetector with long-term stability has proven to be a challenge. Here, using graphene as a template for C60 assembly, we synthesized a large-scale all-carbon hybrid film with inherently strong and tunable UV aborption. Efficient exciton dissociation at the heterointerface and enhanced optical absorption enables extremely high photoconductive gain, resulting in UV photoresponsivity of â¼107 A/W. Interestingly, due to the electron-hole recombination process at the heterointerface, the response time can be modulated by the gate voltage. More importantly, the use of all-carbon hybrid materials ensures robust operation and further allows the demonstration of an exemplary 5 × 5 (2-dimensional) photodetector array. The devices exhibit negligible degradation in figures of merit even after 2 month of operation, indicating excellent environmental robustness. The combination of high responsivity, reliability, and scalable processability makes this new all-carbon film a promising candidate for future integrable optoelectronics.
ABSTRACT
Single-wall carbon nanotubes (SWNTs) have been extensively explored as an ultrafast nonlinear optical material. However, due to the numerous electronic and morphological arrangements, a simple and self-contained physical model that can unambiguously account for the rich photocarrier dynamics in SWNTs is still absent. Here, by performing broadband degenerate and non-degenerate pump-probe experiments on SWNTs of different chiralities and morphologies, we reveal strong evidences for the existence of bandgap renormalization in SWNTs. In particularly, it is found that the broadband transient response of SWNTs can be well explained by the combined effects of Pauli blocking and bandgap renormalization, and the distinct dynamics is further influenced by the different sensitivity of degenerate and non-degenerate measurements to these two concurrent effects. Furthermore, we attribute optical-phonon bath thermalization as an underlying mechanism for the observed bandgap renormalization. Our findings provide new guidelines for interpreting the broadband optical response of carbon nanotubes.
