We report a rare earth (RE)-doped quantum dot-based nanoplatform that regulates lysosomal acidification and enhances macrophage-mediated clearance of intracellular pathogens. By co-doping cadmium selenide quantum dots (CdSe QDs) with ytterbium (Yb3+), erbium (Er3+), and europium (Eu3+), we engineered mixed-phase CdSe:Yb/Er/Eu QDs with tailored crystal field symmetry, broad spectral responsiveness (340-800 nm), and efficient upconversion luminescence. These nanoprobes exhibit strong light-harvesting via RE f-f transitions, size-tunable properties, and dual-mode fluorescence imaging capabilities (upconversion/downconversion). In RAW264.7 macrophages, the QDs demonstrated efficient intracellular localization and, upon near-infrared (800 nm) irradiation, produced a robust photothermal effect (Delta T = 12.8 +/- 0.5 degrees C). Photothermal activation for 48 h selectively upregulated lysosomal acidification-related genes-ATP6V1A (1.39 +/- 0.27-fold) and LAMP1 (1.65 +/- 0.39-fold; P < 0.01)-and significantly increased lysosomal enzymatic activity, including a 68 % rise in cathepsin B activity. This physically triggered "photothermal-gene regulation" approach offers a promising therapeutic avenue for restoring lysosomal function and combating intracellular infections such as Brucella.

Recently optoelectronic synapses generating light-driven electrical memories have played a vital role in the neuromorphic computing of visual perception. However, all the optoelectronic synapses demonstrate photoelectric conversion. Peripheral circuits are used for contact photocurrent measurement, leading to significant energy consumption and impeding the evolution of optical wireless communication. It is crucial to develop noncontact neuromorphic visual perception based on light-driven photonic memories. Herein, we report all-photonic artificial synapses based on photochromic perovskites. Triggered by ultraviolet and visible light pulses, cesium lead iodide bromine induces a structural disorder. Optical transmittance changes induced by the disorder last after the pulses are gone. Next, the photonic memories are propagated in the air and processed by a recurrent neural network. The accuracy of binary image recognition is instantly stabilized at 1.0, and accuracy above 0.8 after 7 epochs is achieved in the recognition of digitals from 0 to 9. The all-photonic synapses realize remote perception with zero in-situ energy consumption and enable artificial sensory systems with low-power computation, remote control, and ultrahigh propagation speed. Optoelectronic synapses are key to artificial visual perception systems based on neuromorphic computing, but they typically rely on photoelectric conversion and peripheral circuits that are energy consuming and prevent optical wireless communication. Here, all-photonic artificial synapses with light-driven optical transmittance memories are fabricated based on photochromic CsPbIBr2 perovskite thin films.

Multi-exciton generation by multi-photon absorption under low-energy photons can be thought a reasonable method to reduce the risk of optical damage, especially in photoelectric quantum dot (QD) devices. The lifetime of the multi-exciton state plays a key role in the utilization of photon-induced carriers, which depends on the dynamics of the exciton generation process in materials. In this paper, the exciton generation dynamics of the photon absorption under low-frequency light in CdSe QDs are successfully detected and studied by the temporal resolution transient absorption (TA) spectroscopy method. Since the cooling time of hot excitons extends while the rate of auger recombination is accelerated when incident energy is increased, the filling time of defect states is irregular, and exciton generation experiences a transition from single-photon absorption to multi-photon absorption. This result shows how to change the excitation. Optical parameters can prolong the lifetime of excitons, thus fully extracting excitons and improving the photoelectric conversion efficiency of QD optoelectronic devices, which provides theoretical and experimental support for the development of QD optoelectronic devices.

An effective method to improve optical properties of perovskite CsPbI3/Br3 is a long-term goal pursued by re-searchers, such as incorporating, mechanism changing and structure optimizing. However, two significant problems still facing challenges including the complex fabrication process and low modulation efficiency. To contribute these, a method of ionic liquid modulation with respect to the photoluminescence PL intensity and peak position was demonstrated. The micro-structure including the information of crystal and bond in MAPbBr3/ I3 soaking in C8H11F3N2O2 and C7H13N2 center dot BF4 was supported by x-ray diffraction XRD patterns and Raman spectrum. A cube-like shape and size distribution mostly in 600-950 nm was imaged by scanning electron mi-croscope. Then, compared with CsPbI3 before soaking in Hall measurement, the carrier concentration was improved about 46.1%, the mobility and resistivity were lowered around 39.2% and 40.2%, respectively. The modulation of intensity and peak position were confirmed by PL spectrum at room temperature. The absorption enhancement in excited state absorbs range was proved by transient absorption. Finally, the mechanism for optical modulation in this paper was systematically explained. The research method proposed in this paper can simplify the research process and improve the optical properties of the materials at the same time.

Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties. This work investigates the third-order nonlinear phenomenon of tungsten trioxide (WO3) thin films. The giant nonlinear absorption and nonlinear refractive index of WO3 thin films were characterized by Z-scan method at 800 nm. We experimentally observed the giant saturable absorption (SA) and nonlinear refractive index of WO3 thin films prepared by the seedless layer hydrothermal method, with SA coefficient being as high as –2.59 × 105 cm⋅GW−1. The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors. The nonlinear refractive index n 2 of WO3 film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm2⋅GW−1. The large third-order nonlinear optical (NLO) response enables WO3 thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.

Manipulating the optical transition in semiconductors at ultrashort timescales is of both fundamental interest and central importance for emerging photonic applications. Traditionally, this manipulation is realized by electrostatic gating via Stark effects or band-gap renormalizations. Here, we report an ultrafast and all-optical route to engineer an indirect transition in core- crown colloidal quantum wells (CQWs), namely, CdSe/CdTe, with a type-II band alignment. Following the intense laser pulse excitation, the indirect band transition energy exhibits a pronounced blueshift-redshift crossover on the picosecond timescale, stemming from the formation and dissipation of the transient electric field (E-field) that forms upon photoexcitation to compensate for the driving force provided by the band offsets. Both the energy shift and dynamics of the transient E-field can be modulated optically by tuning the laser pulse excitation fluence. Our finding demonstrates a strong analogy between the type-II heterojunction and a p-n junction with respect to carrier equilibrium processes, which holds promise to facilitate the integration of CQWs within optical switching networks.

Quantum dots (QDs) laser has become an important way to solve micro-application problems in many fields. However, single wavelength distributed Bragg reflector (DBR) has many limitations in practical applications, such as signal transmission. How to realize multiwavelength DBR lasing output simply is a challenge. To achieve a stable multi-wavelength quantum dots laser in the near-infrared region, the perovskite CsPbI3 QDs laser with DBR structure is developed in this paper. A tetragonal crystal structure with complete bonding information and no defect is explained by X-ray diffractions (XRD) and Raman spectrum. The cross-section morphology of the DBR laser and the surface morphology of QDs is measured by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. An elliptical light propagation field and a double wavelength laser radiation are obtained from the finite-difference time-domain (FDTD) simulation. The output of the three wavelength lasers at 770 nm, 823 nm, and 873 nm is measured. The emission time of a DBR laser is about 2 h, and the average fluorescence quantum yield is 60%. The cavity length selection and energy level model are put in place to clearly see the working mechanism. All the results suggest that an effective and stable CsPbI3 quantum dots DBR laser is realized.

Thin graphene oxide (GO) films have been widely explored for their outstanding optical properties, especially their large optical nonlinear coefficients, and high tunability of optical nonlinear coefficients under photoreduction. In this work, an experimental observation of giant nonlinear optical response in GO films under two different photoreduction mechanisms is reported. After ultraviolet (UV) light‐induced photochemical reduction and continuous wave (CW) laser‐induced photothermal reduction, the nonlinear optical response of reduced graphene oxide (rGO) via the Z ‐scan method using a femtosecond laser beam at a wavelength of 800 nm is characterized. The rGO exhibits a giant optical nonlinearity, especially two‐photon absorption (TPA). A giant TPA coefficient of rGO on the order of ≈ 10 5 cm GW −1 is obtained under two photoreduction mechanisms (photochemistry and photothermal). This is the first time that a large enhancement effect of TPA has been observed in graphene‐based materials, and the TPA coefficient is an order of magnitude higher than the highest value previously reported. The versatile optical nonlinear properties imply a huge potential of the GO film in advanced photonic and optoelectronic devices such as broadband ultrafast optical switching and optical limiting.

Self-assembly of colloidal nanocrystals into ordered superlattices is a powerful approach to enable novel collective properties which are not available in individual colloids. However, to date, it remains a major challenge to develop a practical route to modulate such collective properties for potential photonic applications. Herein, it is shown that the collective emission properties in colloidal quantum well (CQW) superlattices, including emission color and anisotropy, can be effectively modulated in a binary host–guest architecture. The experimental and theoretical results reveal that excitons of the host (i.e., the undoped CQWs) generated by photoexcitation can be controllably harvested by the guest (i.e., the Cu-doped CQWs) for light emission, owing to an exciton hopping assisted exciton trapping process. Such a nano-building block with tunable collective optical properties may enlighten novel colloidal material-based photonic applications, including optical anti-counterfeiting, next-generation liquid crystal displays, and multifunctional biological markers.

Self‐assembly of colloidal nanocrystals into ordered superlattices is a powerful approach to enable novel collective properties which are not available in individual colloids. However, to date, it remains a major challenge to develop a practical route to modulate such collective properties for potential photonic applications. Herein, it is shown that the collective emission properties in colloidal quantum well (CQW) superlattices, including emission color and anisotropy, can be effectively modulated in a binary host–guest architecture. The experimental and theoretical results reveal that excitons of the host (i.e., the undoped CQWs) generated by photoexcitation can be controllably harvested by the guest (i.e., the Cu‐doped CQWs) for light emission, owing to an exciton hopping assisted exciton trapping process. Such a nano‐building block with tunable collective optical properties may enlighten novel colloidal material‐based photonic applications, including optical anti‐counterfeiting, next‐generation liquid crystal displays, and multifunctional biological markers.

Optical modulation is the process of modifying the structure and elemental composition of materials so that the main optical parameters, including amplitude, frequency, and phase, are changed. Currently, much research attention has been directed toward ultrafast dynamics, but the process of modulation is often complex. To simplify the optical modulation process and improve the optical properties of perovskites for semiconductor quantum dot (QD) lasers, the process and physical mechanism underlying graphene QD ultrafast modulation of the optical properties of perovskite CsPbBr3 QDs were investigated. The typical cubic structure and square shape of CsPbBr3 QDs were characterized by transmission electron microscopy and X-ray diffraction, respectively. A luminescent peak centered near 540 nm and Stokes shift of 21.34 nm of CsPbBr3 QDs without graphene QDs were measured by absorption and photoluminescence spectroscopy. A maximum modulation shift of 133 nm and a modulation depth of 900% were achieved in CsPbBr3 with graphene. The results indicated that graphene QDs had the best modulation effect on perovskites when the drop volume was 0.05 mL. The process of ultrafast optical modulation via graphene QDs occurring within 1 ps was confirmed by the transient absorption spectrum. The modulation mechanism of graphene to perovskites is presented for guidance. This paper can be used as a reference for the optical modulation of perovskite materials.

Perovskite solar cells with increasingly pure composition of α‐formamidinium lead triiodide (α‐FAPbI 3 ) perovskite are utilized to set more and more record‐breaking efficiencies. However, pure α‐FAPbI 3 perovskite is unstable and difficult to prepare. Here, a series of bulky alkylammoniums known as the spacer cations (RP cations) of 2D Ruddlesden–Popper perovskites (2D perovskites) are used to prepare α‐FAPbI 3 perovskite films. The deprotonation process of RP cations during annealing removes the in situ generated 2D perovskites from the film, which determines the phase and compositional purity, crystallinity, and stability of α‐FAPbI 3 perovskite films and depends on the design of RP cations. Only a small number of residual RP cations (0.3–2.3%) are found anchoring at grain boundaries. As a result, α‐FAPbI 3 perovskite solar cells prepared from RP cations, especially 2‐thiophenemethylammonium, show higher efficiency and stability than control devices prepared from the most commonly used methylammonium. It is believed that in situ generated 2D perovskites are ideal additives for α‐FAPbI 3 perovskite, because a large addition (20%) of 2D perovskites ensures the preparation of high‐quality phase‐pure α‐FAPbI 3 perovskite films, while a small number of residual RP cations anchored at grain boundaries guarantee the performance and stability of α‐FAPbI 3 perovskite solar cells.

The research of perovskites optical properties is of great value for dual wavelength lasers. However, the phenomenon of double peaks in perovskites photoluminescence (PL) has not been explained systematically, which makes the optical research of perovskites still a challenge. In order to have a deep understanding of the optical properties and applications of new perovskite materials, this phenomenon of MAPbX(3) (X = I inverted exclamation , Br inverted exclamation ) is explained in this paper. The structural characteristics of the materials were investigated by XRD. We found that there were PbBr2 defects in MAPbBr(3) and orthorhombic structure defects in MAPbI(3); By calculating the energy level distribution of perovskites and defects, the PbBr2 in MAPbBr(3) and orthorhombic phase structure in MAPbI(3) can introduce a new energy level into crystals and these two structures lead to the PL peaks of 542 nm and 771 nm, respectively. It is the surface defects in MAPbBr(3) and multi-structures in MAPbI(3) that leads to the two peaks phenomenon of perovskite photoluminescence. All the work explained the mechanism of perovskites PL double peaks. This study can provide theoretical reference for perovskites researches and experimental references for new materials and a promising pathway for dual-wavelength, practical laser based on perovskite crystals.

Kitaev spin liquid (KSL) system has attracted tremendous attention in past years because of its fundamental significance in condensed matter physics and promising applications in fault-tolerant topological quantum computation. Material realization of such a system remains a major challenge in the field due to the unusual configuration of anisotropic spin interactions, though great effort has been made before. Here we reveal that rare-earth chalcohalides REChX (RE=rare earth, Ch=O, S, Se, Te, X=F, Cl, Br, I) can serve as a family of KSL candidates. Most family members have the typical SmSI-type structure with a high symmetry of R-3m and rare-earth magnetic ions form an undistorted honeycomb lattice. The strong spin-orbit coupling of 4f electrons intrinsically offers anisotropic spin interactions as required by Kitaev model. We have grown the crystals of YbOCl and synthesized the polycrystals of SmSI, ErOF, HoOF and DyOF, and made careful structural characterizations. We carry out magnetic and heat capacity measurements down to 1.8 K and find no obvious magnetic transition in all the samples but DyOF. The van der Waals interlayer coupling highlights the true two-dimensionality of the family which is vital for the exact realization of Abelian/non-Abelian anyons, and the graphene-like feature will be a prominent advantage for developing miniaturized devices. The family is expected to act as an inspiring material platform for the exploration of KSL physics.

The physical properties of most 2D materials are highly dependent on the nature of their interlayer interaction. In-depth studies of the interlayer interaction are beneficial to the understanding of the physical properties of 2D materials and permit the development of related devices. Layered magnetic NiPS3 has unique magnetic and electronic properties. The electronic band structure and corresponding magnetic state of NiPS3 are expected to be sensitive to the interlayer interaction, which can be tuned by external pressure. Here, we report an insulator-metal transition accompanied by the collapse of magnetic order during the 2D-3D structural crossover induced by hydrostatic pressure. A two-stage phase transition from a monoclinic (C2/m) to a trigonal $$(P\bar 31m)$$ lattice is identified via ab initio simulations and confirmed via high-pressure X-ray diffraction and Raman scattering; this transition corresponds to a layer-by-layer slip mechanism along the a-axis. Temperature-dependent resistance measurements and room temperature infrared spectroscopy under different pressures demonstrate that the insulator-metal transition and the collapse of the magnetic order occur at ∼20 GPa, which is confirmed by low-temperature Raman scattering measurements and theoretical calculations. These results establish a strong correlation between the structural change, electric transport, and magnetic phase transition and expand our understanding of layered magnetic materials. Moreover, the structural transition caused by the interlayer displacement has significance for designing similar devices at ambient pressure.

Very recently we revealed a large family of triangular lattice quantum spin liquid candidates named rare-earth chalcogenides, which features a high-symmetry structure without structural/charge disorders and spin impurities, and may serve as an ideal platform exploring spin liquid physics. The knowledge of crystalline electric-field (CEF) excitations is an essential step to explore the fundamental magnetism of rare-earth spin systems. Here we employed inelastic neutron scattering (INS) and Raman scattering (RS) to carry out a comprehensive CFE investigation on $NaYbSe_{2}$, a promising representative of the family. By comparison with its nonmagnetic compound $NaLuSe_{2}$, we are able to identify the CEF excitations at 15.8, 24.3 and 30.5 meV at 5K. The selected cuts of the INS spectra are well re-produced with a large anisotropy of $g$ factors ($g_{ab}:g_{c}\sim3:1$). Further, the CEF excitations are explained well by our calculations based on the point charge model. Interestingly, $NaYbSe_{2}$ exhibits an unusual CEF shift to higher energies with increasing temperatures, and the Raman mode close to the first CEF excitation shows an anomalously large softening with decreasing temperatures. The absence of the anomalies in $NaLuSe_{2}$ clearly demonstrates a CEF-phonon coupling not reported in the family. It can be understood in term of the weaker electronegativity of Se. The fact that the smallest first CEF excitation in the sub-family of $NaYbCh_{2}$ is $\sim$ 180K (Ch=O, S, Se), guarantees that the sub-family can be strictly described with an effective S=1/2 picture at sufficiently low temperatures. Interestingly the CEF-phonon coupling revealed here may present alternative possibilities to manipulate the spin systems.

The layered magnetic van der Waals materials have generated tremendous interest due to their potential applications and importance in fundamental research. Previous x-ray diffraction (XRD) studies on the magnetic van der Waals compound VI3, revealed a structural transition above the magnetic transition but output controversial analysis on symmetry. In this paper we carried out polarized Raman scattering measurements on VI3 from 10 K to 300 K, with focus on the two A g phonon modes at ∼ 71.1 cm−1 and 128.4 cm−1. Our careful symmetry analysis based on the angle-dependent spectra demonstrates that the crystal symmetry can be well described by C 2h rather than D 3d both above and below structural phase transition. We further performed temperature-dependent Raman experiments to study the magnetism in VI3. Fano asymmetry and anomalous linewidth drop of two A g phonon modes at low temperatures, point to a significant spin–phonon coupling. This is also supported by the softening of 71.1-cm−1 mode above the magnetic transition. The study provides the fundamental information on lattice dynamics and clarifies the symmetry in VI3. And spin–phonon coupling existing in a wide temperature range revealed here may be meaningful in applications.

Colloidal perovskite CsPbX3 (X = Cl, Br, I) nanocrystals (CPNCs)/polymers composites have attracted extensive attention due to their potential to be developed as flexible phosphor films for lighting applications. However, to maintain high quantum efficiency and photo stability of CPNCs in such composites remains a daunting challenge. Here, we have demonstrated a layered composite structure consisting of CPNCs and polydimethylsiloxane (PDMS) with multi-color emission and long-term stability. By tuning the molar ratio between CsPbCl1.58Br1.42 and CsPbBr1.35I1.65, flexible fluorescent films as down-converter layers with a high luminescent efficiency and a controllable color temperature spanning from 3194 K to 5901 K have been demonstrated. Furthermore, due to embedding inside such composites, the quantum efficiency of CPNCs exhibited negligible changes during seven months in ambient conditions. The carrier dynamics based on time-resolved photoluminescence (PL) and transient absorption spectroscopy reveal that the hot electron tunneling and trapping process are significant in the composite film. This work provides a good understanding of CPNC materials in complex composite for the development of flexible, robust, color controllable fluorescent films for lighting applications.

Beyond the conventional electron pairing mediated by phonons, high-temperature superconductivity in cuprates is believed to stem from quantum spin liquid (QSL). The unconventional superconductivity by doping a spin liquid/Mott insulator, is a long-sought goal but a principal challenge in condensed matter physics because of the lack of an ideal QSL platform. Here we report the pressure induced metallization and possible unconventional superconductivity in NaYbSe_2, which belongs to a large and ideal family of triangular lattice spin liquid we revealed recently and is evidenced to possess a QSL ground state. The charge gap of NaYbSe2 is gradually reduced by applying pressures, and at  20 GPa the crystal jumps into a superconducting (SC) phase with Tc   5.8 K even before the insulating gap is completely closed. The metallization is confirmed by further high-pressure experiments but the sign of superconductivity is not well repeated. No symmetry breaking accompanies the SC transition, as indicated by X-ray diffraction and low-temperature Raman experiments under high pressures. This intrinsically connects QSL and SC phases, and suggests an unconventional superconductivity developed from QSL. We further observed the magnetic-field-tuned superconductor-insulator transition which is analogous to that found in the underdoped cuprate superconductor La_2-xSr_xCuO_4. The study is expected to inspire interest in exploring new types of superconductors and sheds light into the intriguing physics from a spin liquid/Mott insulator to a superconductor.