A cocrystal strategy with a simple preparation process is developed to prepare novel materials for near-infrared photothermal (PT) conversion and imaging. DBTTF and TCNB are selected as electron donor (D) and electron acceptor (A) to self-assemble into new cocrystals through non-covalent interactions. The strong D-A interaction leads to a narrow band gap with NIR absorption and that both the ground state and lowest-lying excited state are charge transfer states. Under the NIR laser illumination, the temperature of the cocrystal sharply increases in a short time with high PT conversion efficiency (η=18.8 %), which is due to the active non-radiative pathways and inhibition of radiative transition process, as revealed by femtosecond transient absorption spectroscopy. This is the first PT conversion cocrystal, which not only provides insights for the development of novel PT materials, but also paves the way of designing functional materials with appealing applications.

www.advancedsciencenews.com www.small-methods.com an inorganic or organic cation (Cs + , CH 3 NH 3 + , NH 2 CHNH 2 + , etc.), M is a divalent metallic cation (Pb 2+ , Sn 2+ , Mn 2+ , Fe 2+ , etc.), and X is halogen anion (I − , Br − , Cl − ). [28][29][30] Since 2009, perovskites have gained worldwide attention due to their unprecedented success in photovoltaics. [31][32][33][34][35][36] The power conversion of solution-processed CH 3 NH 3 PbX 3 (MAPbX 3 ) perovskite solar cells has increased from 3.8% to 22.1% within a few years. [37][38][39][40][41][42] Although there is still some debate, it is widely accepted that the high power conversion efficiency of MAPbX 3 is attributed to the high absorption coefficient (≈10 4 cm −1 ), balanced and long diffusion length (≈100 nm to 100 µm), low density of defect states (10 9 -10 10 cm −3 ) and bipolar carrier-transport property. [31,33,34] As a direct-bandgap semiconductor, perovskites also show wide-band tunable emission color and high quantum yield, holding important potential applications in light sources, for example. [40,[43][44][45] Prior to the rapidly developing studies in solar cells, perovskites have been studied as light-emittingdiode (LED) devices for a long time. [46][47][48] In particular, recent studies on photophysical properties, structure engineering, and device development have led to the rapid progress of coherent and incoherent perovskite photonic sources. [44,[49][50][51][52][53][54][55] For example, several groups have demonstrated perovskite LEDs with external quantum efficiency of ≈8-12% using solutionprocessed and thermally evaporated quasi-two-dimensional perovskite thin films, etc. [44,51] Furthermore, perovskite nanostructures including NWs, NPs, and quantum dots (QDs) are also attracting more and more attention for exploring nanophotonic and quantum devices, including single-photon sources, optical detectors, transistors, optical sensors, etc. [56][57][58][59] In a nutshell, despite the Pb toxicity and poor stability, perovskites have been attracting more and more attention in divergent research areas. These fundamental studies on and applications of perovskite photonic sources could extensively push forward our present energy and communication technology.With high absorption coefficient and low density of defects, perovskites are excellent gain materials for the development of high-performance lasing devices. More interestingly, thanks to the long-distance ambipolar carrier-transport properties, perovskites could greatly raise the possibility of realizing electrically driven microlasers and nanolasers. In 2014, Xing et al. demonstrated the first amplification of spontaneous emission (ASE) of CH 3 NH 3 PbX 3 perovskite thin film, which had been solution processed at low temperature. [60] Through embedding CH 3 NH 3 PbI 3−x Cl x perovskite thin films into a distributed Bragg reflector Fabry-Pérot (F-P) cavity, Deschler et al. demonstrated room-temperature perovskite lasing. [49] Beyond these thin films, perovskite nanostructures including NP...

All-inorganic perovskite micro/nanowire materials hold great promises as nanoscale coherent light source due to their superior optical and electronic properties. The coupling strength between exciton and photon in this system is important for their optical application, however, is rarely studied. In this work, we demonstrated the strong coupling of exciton-photon and polariton lasing in high quality CsPbBr3 micro/nanowires synthesized by a CVD method. By exploring spatial resolved PL spectra of CsPbBr3 cavity, we observed mode volume dependent coupling strength with a vacuum Rabi splitting up to 656 meV, as well as significant increase in group index. Moreover, low threshold polariton lasing was achieved at room temperature within strong coupling regime; the polariton characteristic is confirmed by comparing lasing spectra with waveguided output spectra and the dramatically reduced lasing threshold. Our present results provide new avenues to achieve high coupling strengths potentially enabling application of exciting phenomena such as Bose-Einstein condensation of polaritons, efficient light-emitting diodes and lasers.

1D nanowires of all-inorganic lead halide perovskites represent a good architecture for the development of polarization-sensitive optoelectronic devices due to their high absorption efficient, emission yield, and dielectric constants. However, among as-fabricated perovskite nanowires with the lateral dimensions of hundreds nanometers so far, the optical anisotropy is hindered and rarely explored owing to the invalidating of electrostatic dielectric mismatch in the physical dimensions. Here, well-aligned CsPbBr and CsPbCl nanowires with thickness T down to 15 and 7 nm, respectively, are synthesized using a vapor phase van der Waals epitaxial method. Strong emission anisotropy with polarization ratio up to ≈0.78 is demonstrated in the nanowires with T < 40 nm due to the electrostatic dielectric confinement. With the increasing of thickness, the polarization ratio remarkably reduces monotonously to ≈0.17 until T ≈140 nm; and further oscillates in a small amplitude owing to the wave characteristic of light. These findings not only represent a demonstration of perovskite-based polarization-sensitive light sources, but also advance fundamental understanding of their polarization properties of perovskite nanowires.

breakthrough in power conversion efficiency of 22.1%, [19] comparable to conventional silicon based solar cell. Wavelength tunable LEDs and optically pumped lasers have been achieved by simply changing the ration of halide anions. However, there are still challenges in electroluminescence with high efficiency and electrically pumped lasers. [20] One intrinsic limitation in perovskite is relatively low exciton binding energy that cannot suppress the exciton ionization in the working condition devices. [21] For example, microwave photoconductance and photoluminescence (PL) study revealed exciton binding energy of 18-32 meV [22,23] in MAPbI 3 , comparable to room temperature thermal energies of K B T ≈ 25 meV. By substitution doping of Cl, larger exciton binding energy of 62.3 ± 8.9 meV can be obtained in perovskite thin film. [24] In MAPbBr 3 quantum dots, exciton binding energy can be as large as 375 meV in comparison to their bulk counterpart of 65 meV. [25] In this regard, low dimensional perovskite single crystals with optical or size confinement are becoming promising in complementing their bulk counterparts. With reduced dimensionality, lead halide perovskite provides a platform where exciton behavior, such as exciton-photon interaction [26,27] and exciton binding energy, [28] can be well modulated, giving the pathway to obtain highly efficient optoelectronic devices.

Facile and mass production of intrinsic and defect-free 2D QSs from bulk layered materials is achieved via a unified top-down method.

Single-crystal perovskites with excellent photophysical properties are considered to be ideal materials for optoelectronic devices, such as lasers, light-emitting diodes and photodetectors. However, the growth of large-scale perovskite single-crystal films (SCFs) with high optical gain by vapor-phase epitaxy remains challenging. Herein, we demonstrated a facile method to fabricate large-scale thin CsPbBr3 SCFs (∼300 nm) on the c-plane sapphire substrate. High temperature is found to be the key parameter to control low reactant concentration and sufficient surface diffusion length for the growth of continuous CsPbBr3 SCFs. Through the comprehensive study of the carrier dynamics, we clarify that the trapped-related exciton recombination has the main effect under low carrier density, while the recombination of excitons and free carriers coexist until free carriers plays the dominate role with increasing carrier density. Furthermore, an extremely low-threshold (∼8 μJ cm–2) amplified spontaneous emission was achieved at room temperature due to the high optical gain up to 1255 cm–1 at a pump power of 20 times threshold (∼20 P th). A microdisk array was prepared using a focused ion beam etching method, and a single-mode laser was achieved on a 3 μm diameter disk with the threshold of 1.6 μJ cm–2. Our experimental results not only present a versatile method to fabricate large-scale SCFs of CsPbBr3 but also supply an arena to boost the optoelectronic applications of CsPbBr3 with high performance.

Miniaturized laser is the key element for integrated on-chip photonic device. Semiconductor materials are excellent candidates for gain medium of microscale laser, especially for nanowire (NW) based lasers. However, optical diffraction law constrains the footprint of photonic NW based device with the scale of half wavelength. [1] While in hybrid metal-semiconductor plasmonic nanostructures, photon energy could be coupled into collective electron oscillations in the form of surface plasmon polaritons (SPPs) at a metal-dielectric interface, [2][3][4] which therefore provide an effective solution to overcome optical diffraction limit. Similar to photonic laser, plasmonic lasers get amplification of SPPs by energy transfer from nonradiative part excitons of semiconductor material, where semiconductor severs as the gain media driving the inversion of SPP population at the metal-dielectric interface. [5][6][7] The SPP lasers show superior capabilities in strong light-matter interaction, which have potential applications in integrated photonics, biosensors, and quantum information technologies. [8][9][10] A series of inorganic II-VI and III-V compound semiconductor plasmonic NW lasers have been achieved in GaN, ZnO, and CdS NWs [11][12][13][14][15] at room temperature, because these NWs gain medium produce sufficient gain to overcome the high losses in metals. The fabrication procedures usually require extreme conditions such as high-temperature or low-pressure conditions, leading to high cost. However, till now the thresholds of the resulting lasers are still high, low-cost gain materials with excellent gain characteristics are in urgent need to be exploited to overcome these problems.Recently, organic-inorganic lead halide perovskites (CH 3 NH 3 PbX 3 , X = Cl, Br, I) have attracted intensive attentions for their huge potential in photovoltaics, with a power conversion efficiency exceeded 22.1% in solar cells. [16] On the other hand, lead halide perovskites have emerged as promising optical gain materials for achieving low-threshold plasmonic lasers owing to their excellent optical properties in a wide spectrum range, such as large absorption coefficients, high photoluminescence (PL) quantum yield, and low nonradiative recombination rates. [17][18][19][20][21] In past few years, SPP lasers have been investigated in hybrid perovskites. For instance, Kao et al. demonstrated enhanced localized surface plasmonic lasing performance in solution-processed CH 3 NH 3 PbI 3 perovskite films in Plasmonic nanolaser holds great potential in breaking down the diffraction limit of conventional optics to the deep sub-wavelength regime and in ultrafast lasing dynamics. However, plasmonic laser devices are constrained in practical applications due to their high cost and high thresholds. All-inorganic cesium lead halide perovskites are promising solutions for their excellent optical gain properties and high emission efficiency. In this work, high-quality single-crystalline CsPbBr 3 perovskite nanowires (NWs) are synthesized by chemical ...