Natural and polyanionic heparin polysaccharide functionalized upconversion nanoparticles for highly sensitive and selective ratiometric detection of pesticide.

Pesticide contamination is a global concern, threatening human health and food safety. Herein, we developed heparin (HEP) functionalized upconversion nanoparticles (UCNPs)-based ratiometric nanosensor for the sensitive detection of 2,6-dichloro-4-nitroaniline (DCN) pesticide via inner filter effect. The strategy for HEP functionalization of UCNPs is based on adjusting the surface potentials of UCNPs with polyanionic HEP through the electrostatic interaction. UCNPs (NaYbF4:Gd/Y/Tm@NaYbF4@NaYF4) was designed with core-shell-shell structure and extra sensitizer layer for efficient and strong upconversion luminescence (UCL) in the range of UV to NIR. After incorporation of DCN, the upconverted UV emission of UCNPs-HEP ratiometric nanosensor was considerably quenched with the NIR UCL at 800 nm remaining unchanged as internal standard. The UCNPs-HEP ratiometric nanosensor can achieve outstandingly selective and sensitive detection of DCN at the wide linear range of 5-300 µM with a detection limit of 0.41 µM. The remarkable applicability of the UCNPs-HEP ratiometric nanosensor was verified in apple, cucumber and grapes samples. The developed UCNPs-HEP ratiometric nanosensor with excellent biocompatibility and water dispersion capability, is promising for convenient, selective and sensitive sensing of DCN towards food and aqueous samples.

Broadband near-infrared luminescence in a cubic pyrophosphate Al0.5Ta0.5P2O7:Cr3+ phosphor for multi-functional applications.

Near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) are considered as next-generation of NIR light sources for spectroscopy. However, it is still a challenge to develop an inexpensive broadband NIR phosphor with relatively long-wavelength (λem > 800 nm) emission. In this work, an octahedral Al3+-containing pyrophosphate Al0.5Ta0.5P2O7 with a cubic structure was chosen as a host for Cr3+. Synthesizing this material indicates that this phosphor exhibits a broadband NIR emission peaking at 850 nm with a full width at half maximum (FWHM) of 155 nm under 465 nm excitation. The crystal structure, morphology, local structure, and photoluminescence properties of this material were investigated in detail. The results revealed a full understanding of this new material. A NIR pc-LED device fabricated by using this material combined with a 450 nm LED chip generates a NIR output power of 10.7 mW and a NIR photoelectric conversion efficiency of 3.4% under a 100 mA driving current, which shows the possibility of this material to be utilized in NIR pc-LED applications. Moreover, this material exhibits a linear relationship between emission intensity, decay time and temperature in a wide temperature range, implying that excellent multi-model temperature sensing applications can be expected.

Broadband and strength-switchable circular dichroism in a Ge2Sb2Te5-based metasurface.

Circular dichroism (CD) is highly required in the applications of biological detection and analytical chemistry. In this paper, we achieved a giant, broadband, and strength-switchable CD effect in a quadruple z-shaped G e 2 S b 2 T e 5 (GST) metasurface. At the amorphous state of GST (a-GST), the giant CD reaches 0.92 and the width of the absorption >0.80 is about 100 nm. The giant and broadband CD originates from polarization selective excitations of Mie resonances and the coupling between subunit resonators. With the transition from a-GST to crystalline GST, CD could be dynamically switched from 0.92 to 0.05. The GST-based metasurfaces with giant and wide-range switching CD will promote the development of active chiral devices.

Broadband 1.0†µm emission in Nd3+/Yb3+ co-doped phosphate glasses and fibers for photonic applications.

In this work, the spectroscopic properties of 1.0 µm emission in Nd3+/Yb3+ co-doped phosphate glasses were systematically investigated under 808 nm excitation. Notably, broadband 1.0 µm emission with a full width at half maximum (FWHM) of 96 nm was obtained in the phosphate glass doped with 2 mol.% Nd2O3 and 1 mol.% Yb2O3. In addition, the energy transfer microscopic parameter and transfer efficiency were analyzed. What is more, multimaterial fibers with Nd3+/Yb3+ co-doped phosphate glass core and silicate cladding were successfully drawn by using the molten core method. An intense 1.0 µm amplified spontaneous emission (ASE) can be realized in a 3 cm long multimaterial fiber. More importantly, the FWHM of the ASE can reach as large as 60 nm when excited at 976 nm. These results demonstrate that the Nd3+/Yb3+ co-doped phosphate glasses and fibers are promising gain materials for amplifier and laser applications in photonics.

Broadband near-infrared amplified spontaneous emission of Er3+-doped germanate glass fiber.

Er3+-doped glass and fiber are very attractive for near-infrared (NIR) lasers and photonic applications. In this work, the full width at half maximum (FWHM) of NIR fluorescence emission of the Er3+-doped germanate glass can be broadened from 72 to 99 nm when Al2O3 was added. In addition, the spectroscopic properties, including absorption and emission spectra, Judd-Ofelt intensity parameters, absorption and emission cross sections, gain coefficient, and fluorescence lifetime, of the Al2O3-modified germanate glass were systematically investigated. What is more, silicate-clad heavily Er3+-doped germanate core multimaterial fibers were successfully drawn by a rod-in-tube method. Notably, broadband NIR amplified spontaneous emission (ASE) with an FWHM of 120 nm was achieved in this new fiber. To the best of our knowledge, this is the largest FWHM reported for Er3+-doped germanate glass fibers. These results suggest that the as-drawn Er3+-doped germanate glass fiber with superior performances is a promising candidate for broadband optical amplification.

Dynamically Adjusting Borophene-Based Plasmon-Induced Transparency in a Polymer-Separated Hybrid System for Broadband-Tunable Sensing.

Borophene, an emerging two-dimensional (2D) material platform, is capable of supporting highly confined plasmonic modes in the visible and near-infrared wavebands. This provides a novel building block for light manipulation at the deep subwavelength scale, thus making it well-suited for designing ultracompact optical devices. Here, we theoretically explore a borophene-based plasmonic hybrid system comprising a continuous borophene monolayer (CBM) and sodium nanostrip gratings (SNGs), separated by a polymer spacer layer. In such a structure, a dynamically tunable plasmon-induced transparency (PIT) effect can be achieved by strongly coupling dark and bright plasmonic modes, while actively controlling borophene. Here, the bright mode is generated through the localized plasmon resonance of SNGs when directly excited by TM-polarized incident light. Meanwhile, the dark mode corresponds to a propagating borophene surface plasmon (BSP) mode in the CBM waveguide, which cannot be directly excited, but requires phase matching with the assistance of SNGs. The thickness of the polymer layer has a significant impact on the coupling strength of the two modes. Owing to the BSP mode, highly sensitive to variations in the ambient refractive index (RI), this borophene-based hybrid system exhibits a good RI-sensing performance (643.8 nm/RIU) associated with a wide range of dynamically adjustable wavebands (1420-2150 nm) by tuning the electron density of borophene. This work offers a novel concept for designing active plasmonic sensors dependent on electrically gating borophene, which has promising applications in next-generation point-of-care (PoC) biomedical diagnostic techniques.

Understanding the broadband near-infrared luminescence in a highly distorted garnet Ca4HfGe3O12:Cr3+ phosphor.

Broadband near-infrared (NIR) spectroscopy generated from a phosphor-converted light-emitting diode (pc-LED) has multifunctional applications, including food-quality analysis, bio-medical and night-vision, stimulating the demand for developing various NIR phosphors with desired properties. Herein, we selected a highly distorted garnet Ca4HfGe3O12 as the host and explored the near-infrared luminescence of Cr3+. As expected, this material achieved a long-wavelength NIR emission and excellent absorption efficiency based on the effect of Jahn-Teller distortion. The synthesized Ca4HfGe3O12:Cr3+ phosphor exhibits a broadband NIR emission peaking at 840 nm with a full width at half maximum of 150 nm, and the absorption efficiency reaches 48.0%. However, the internal quantum efficiency of the 6 mol% Cr3+-doped sample was measured to be only 35.3% and the integral emission intensity at 373 K kept only 60.1% of the initial intensity. The possible reasons for the unsatisfactory internal quantum efficiency and thermal stability were systematically analyzed, which provided a comprehensive understanding of the relationship between the crystal structure and the luminescent properties of Cr3+-activated garnet-type phosphors. Nevertheless, the as-prepared NIR pc-LED device exhibits a NIR output of 16.52 mW with a NIR photoelectric conversion efficiency of 5.92% driven by 100 mA current, indicating the potential of this material for application in NIR pc-LED.

An efficient and thermally stable near-infrared phosphor derived from the Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) garnet family.

A broadband near-infrared (NIR) light source based on a phosphor-converted light-emitting diode (pc-LED) has attracted increasing interest to be used in non-destructive examination, security-monitoring and medical diagnosis fields, which stimulates the exploration of NIR phosphors with high performance. Herein, a series of Cr3+-activated garnet Ln3ScInGa3O12:Cr3+ (Ln = La, Gd, Y, and Lu) phosphors were reported, allowing an emission peak ranging from 726 to 822 nm. Among them, Y3ScInGa3O12:Cr3+ with an optimized Cr3+-doping concentration of 6 mol% exhibits a high internal quantum efficiency (IQE = 83.1%) and excellent absorption efficiency (AE = 44.2%) under 450 nm blue light excitation, enabling an external quantum efficiency as high as 36.7%. Moreover, this material can maintain 93.0% of the initial intensity when heated up to 423 K, implying outstanding thermal stability. Finally, a prototype NIR pc-LED device was fabricated by coating the optimized phosphor on a 455 nm LED chip, which generates a broadband NIR emission with a peak located at 765 nm and a full width at half maximum of 127 nm. The NIR output power and NIR photoelectric conversion efficiency of this device were found to be 38.01 mW and 11.0%, respectively, under 100 mA driving current, demonstrating the feasibility of this material to be applied in NIR pc-LEDs.

Enhanced 2-µm and upconversion luminescence properties regulated by network structure in Ho3+/Yb3+ co-doped germanate laser glasses.

Rare-earth (RE) ions doped laser glass has attracted the interest of many researchers because of its numerous potential applications in planar waveguides and fiber lasers. In this work, the 2-µm and upconversion luminescence properties of Ho3+ are simultaneously enhanced through the design of components used to regulate the network structure of the germanate glass. Furthermore, the thermal, structural, and spectroscopic properties of the Ho3+/Yb3+ co-doped germanate laser glass are systematically investigated. It is noted that the calculated gain coefficient of the Nb2O5 modified germanate laser glass can reach as high as 3.05 cm-1 at 2047 nm. These results suggest that the prepared germanate laser glass with superior performances is a promising candidate for 2-µm mid-infrared laser materials applications.

Producing Tunable Broadband Near-Infrared Emission through Co-Substitution in (Ga1-xMgx)(Ga1-xGex)O3:Cr3.

Broadband near-infrared (NIR) phosphors are in high demand for creating "smart" NIR phosphor-converted light-emitting diode (pc-LED) sources. In this work, a series of Cr3+-substituted NIR-emitting materials with highly efficient, broad, tunable emission spectra are achieved by modifying the simple oxide Ga2O3 using [Mg2+-Ge4+] and [Ga3+-Ga3+] co-unit substitution. The results show that the emission peak can be shifted from 726 to 830 nm while maintaining a constant excitation peak in the blue light region, enabling extensive application. The optical properties stem from changes in the Cr3+ crystal field environment upon substitution. Intriguingly, the temperature-dependent photoluminescence emission peak position shows virtually no change in the [Mg2+-Ge4+] co-substituted materials. This abnormal phenomenon is found to be a comprehensive embodiment of a weakening crystal field environment (red-shift) as the temperature increases and reduced local structure distortion (blue-shift) with increasing temperature. The high quantum yield, NIR emission, and net-zero emission shift as a function of temperature make this phosphor class optimal for device incorporation. As a result, their performance was studied by coating the phosphor on a 450 nm emitting LED chip. The fabricated device demonstrates an excellent NIR output power and NIR photoelectric conversion efficiency. This study provides a series of efficient, tunable, broadband NIR materials for spectroscopy applications and contributes to the basic foundation of Cr3+-activated NIR phosphors.

Multifunctional metasurfaces for switchable polarization selectivity and absorption.

A multifunctional metasurface capable of dynamic control for polarization selectivity and absorption is proposed by controlling the phase of Ge2Sb2Te5 (GST) in the near-infrared region. At amorphous state of GST (a-GST), the proposed GST strip array realized polarization selectivity in transmission-reflection integrated modes. The high-efficiency asymmetric transmission (AT = 0.92) and asymmetric reflection (AR = -0.82) are both obtained by selectively exciting Mie multipole resonances. With the transition from a-GST to crystalline (c-GST) state, the giant polarization selectivity almost disappeared, and the absorptions climb from < 0.1 to > 0.9. The maximum modulation depth reaches 94%. The mechanism of the dynamic switching between polarization selectivity and absorption is quantitively analyzed via multipole expansion. The GST based metasurfaces simultaneously possess excellent switchable capability for AT, AR, and absorption without refabricating structures, which is promising to the applications for next generation optical devices.

Active metasurface in the near-infrared region by gating ultrathin TiN films.

Ultrathin titanium nitride (TiN) films have become a novel material flatform for constructing active metasurfaces in the near-infrared region. In this Letter, we numerically achieved the dual functions of switchable linear dichroism (LD) and tunable perfect absorption in a G-shape gold resonators/TiN film hybrid metasurface by gating ultrathin TiN films. As the carrier density of TiN decreases, the modulation depth for LD strength is about 70% at 1211 nm. Meanwhile, the response wavelength of perfect absorption (∼1) shifts to the blue by around 130 nm with a change of carrier density of 12%. Our proposed active metasurface with the capability of strength-switchable LD and wavelength-tunable perfect absorption has considerable potential in dynamic electro-optic modulation and flat photonic devices with reconfigurable functionalities.

Enhanced circular dichroism in Ge2Sb2Te5-loaded metasurface.

Circular dichroism (CD) is originally obtained from three-dimensional spiral structures by simultaneously exciting electric and magnetic resonances. To simplify construction, multilayer stacked asymmetric structures and the symmetric structures relying on oblique incidence are proposed for enhancing CD. Herein, we achieved the enhancement of dual-waveband CD by adding a Ge2Sb2Te5 (GST) layer on the top of a Z-shape gold array in a normally incident system. Benefited from the polarization selective excitations of electric and magnetic dipole resonances, the CD in a simple planar structure is immensely enhanced from near zero to 0.73 at 1.58 µm. Furthermore, the CD strengths is dynamically tuned by controlling the phase of GST. With the GST phase transition from amorphous (a-GST) to crystalline state (c-GST), CD magnitudes are switched by about 0.73 and 0.27 at dual wavebands respectively. The enhancement of CD by adding a layer on a simple planar array offers a new method for designing planar metasurfaces with strong chirality.

Achieving a tunable and ultra-broadband near-infrared emission in the Ga2-2xZnxGexO3:Cr3+ phosphor.

Near-infrared (NIR) spectroscopy (700-1100 nm) based on a phosphor-converted light-emitting diode (pc-LED) has multi-functional applications in bio-imaging, night-vision, and food quality analysis, simulating the development of efficient and ultra-broadband NIR phosphors. Herein, a series of tunable and ultra-broadband NIR phosphor Ga2-2xZnxGexO3:Cr3+ was successfully produced by a [Zn2+-Ge4+] unit co-substituting a [Ga3+-Ga3+] unit in Ga2O3:Cr3+. With the increasing amount of [Zn2+-Ge4+] incorporation, the emission peak can be tuned from 726 to 808 nm, and the maximum FWHM can be extended from 126 to 190 nm. However, the excitation peak position remained nearly unchanged in the blue light region, enabling this material to perfectly match the InGaN blue LED chip. Although the gradually enhanced electron-lattice coupling and low energy barrier for thermal quenching caused by this co-substitution lead to a decrease in the photoluminescence quantum yield (PLQY) and thermal stability, respectively, the absolute values of these two criteria can be well maintained. Finally, to evaluate the practical applications, prototype NIR pc-LEDs were fabricated using these materials combined with 450 nm LED chips. Under the same conditions, the NIR output power and photoelectronic conversion efficiency of these devices are superior to those fabricated using the well-known ScBO3:Cr3+ phosphor. These results demonstrate that this series of materials with tunable and ultra-broadband NIR emissions has great potential for NIR pc-LED applications.

Design and simulation of a GST-based metasurface with strong and switchable circular dichroism.

Circular dichroism (CD) is required in the applications of biological detection, analytical chemistry, etc. Here, we numerically demonstrated large-range switchable CD by controlling the phase change of Ge2Sb2Te5 (GST) in a zigzag array. At the amorphous state of GST (a-GST), the strong and dual-waveband CD effects are realized via the selective excitations of electric, magnetic, and toroidal resonances. With the transition from a-GST to crystalline state GST, CD strengths are tailored dynamically in large ranges. In detail, the CD magnitudes change by about 0.93 and the modulation depths exceed 94% at dual wavebands. The strong CD effects and large-range switch capability in the GST-based metasurfaces will boost the development of active chiroptical devices.

Temperature-Dependent Optical Properties of Perovskite Quantum Dots with Mixed-A-Cations.

In this work, metal halide perovskite quantum dots (QDs) with Formamidinium (FA) and Cs mixed cations were fabricated using a solution-processed method at room temperature. By controlling Cs doping ratios in a precursor, the optical properties of mixed-cation perovskite QDs were systematically studied. With the increase in Cs ion doping, the photoluminescence (PL) spectra of perovskite QDs were blueshifted, which was mainly due to the smaller radius of Cs ions than those of FA. Temperature-dependent PL spectra were conducted on mixed-cation perovskite QDs. As the temperature gradually increased from 4 K to 300 K, PL peaks were blue shifted, and full-width at half maximum (FWHM) was widened, which was directly related to lattice thermal expansion and the carrier-photon coupling effect under temperature variation. At the same time, excess Cs ion doping had a prominent influence on optical properties at low temperatures, which was mainly due to the introduction of detrimental defects in perovskite crystals. Therefore, it is particularly important to control doping concentration in the preparation of high-quality perovskite QDs and efficient photoelectric devices.

Efficient and Thermally Stable Broad-Band Near-Infrared Emission in a KAlP2O7:Cr3+ Phosphor for Nondestructive Examination.

Broad-band near-infrared (NIR) phosphors are essential to assembling portable NIR light sources for applications in spectroscopy technology. However, developing inexpensive, efficient, and thermally stable broad-band NIR phosphors remains a significant challenge. In this work, a phosphate, KAlP2O7, with a wide band gap and suitable electronic environment for Cr3+ equivalent substitution was selected as the host material. The synthesized KAlP2O7:Cr3+ material exhibits a broad-band emission covering 650-1100 nm with a peak centered at 790 nm and a full width at half-maximum (fwhm) of 120 nm under 450 nm excitation. The internal quantum efficiency (IQE) was determined to be 78.9%, and the emission intensity at 423 K still maintains 77% of that at room temperature, implying the high efficiency and excellent thermal stability of this material. Finally, a NIR phosphor-converted light-emitting diode (pc-LED) device was fabricated by using the as-prepared material combined with a 450 nm blue LED chip, which presents a high NIR output power of 32.1 mW and excellent photoelectric conversion efficiency of 11.4% under a drive current of 100 mA. Thus, this work not only provides an inexpensive broad-band NIR material with high performance for applications in NIR pc-LEDs but also highlights some strategies to explore this class of materials.

Trap-free exciton dynamics in monolayer WS2via oleic acid passivation.

Two-dimensional transition metal dichalcogenides have attracted a great deal of attention in the past few decades owing to their attractive optoelectronic properties. However, their widespread utility in photonic devices and components is still limited owing to their weak photoluminescence. While various treating methods are in place to improve the photoluminescence yield, the impact of these treatments on the excited state (especially exciton) dynamics in these two-dimensional materials remains ill defined. In this work, exciton dynamics in pristine and oleic acid-treated monolayer WS2 were comprehensively studied through various ultrafast experimental techniques. We demonstrate that oleic acid effectively passivates the defect states in as-fabricated WS2, resulting in trap-free exciton dynamics and exciton annihilation rate reduction, which leads to stronger steady-state photoluminescence and longer photoluminescence lifetime. These results provide valuable information on the intrinsic exciton dynamics in monolayer WS2, which could also be applicable in other two-dimensional transition metal dichalcogenides and help improve optoelectronic device performance.

Efficient and Tunable Luminescence in Ga2-xInxO3:Cr3+ for Near-Infrared Imaging.

Broadband near-infrared (NIR) emitting materials are in great demand as next-generation smart NIR light sources. In this work, a Cr3+-substituted phosphor capable of efficiently converting visible to NIR light is developed through the solid solution, Ga2-xInxO3:Cr3+ (0 ≤ x ≤ 0.5). The compounds were prepared using high-temperature solid-state synthesis, and the crystal and electronic structure, morphology, site preference, and photoluminescence properties are studied. The photoluminescence results demonstrate a high quantum yield (88%) and impressive absorption efficiency (50%) when x = 0.4. The NIR emission is tunable across a wide range (713-820 nm) depending on the value of x. Moreover, fabricating a prototype of a phosphor-converted NIR light-emitting diode (LED) device using 450 nm LED and the [(Ga1.57Cr0.03)In0.4]O3 phosphor showed an output power that reached 40.4 mW with a photoelectric conversion efficiency of 25% driven by a current of 60 mA, while the resulting device was able to identify damaged produce that was undetectable using visible light. These results demonstrate the outstanding potential of this phosphor for NIR LED imaging applications.

Ultrafast nonequilibrium dynamic process of separate electrons and holes during exciton formation in few-layer tungsten disulfide.

Femtosecond transient absorption spectroscopy has been employed to unravel separate initial nonequilibrium dynamic processes of photo-injected electrons and holes during the formation process of the lowest excitons at the K-valley in few-layer tungsten disulfide. Charge carrier thermalization and cooling, as well as concomitant many-body effects on the exciton resonances, are distinguished. The thermalization of holes is observed to be faster than that of electrons. Both of them proceed predominantly via carrier-carrier scattering, as evidenced by the observed dependence of the thermalization time on pump fluences. The fluence dependent time constants also suggest that the subsequent cooling for electrons is probably dominated by acoustic phonons, whereas for holes it is mostly controlled by LO phonons. An extremely fast red- and blue-shift crossover followed by a slow blue-shift of exciton resonance was observed in the temporal evolution of exciton resonances by resonant exciton A excitation. The rapid red-shift could be due to the strong screening of the Coulomb interaction between quasi-free charge carriers in electron-hole plasma. The subsequent slow blue-shift is the net result of the competition among many-body effects in the hot-exciton cooling process. Our findings elucidate the carrier-selective ultrafast dynamics and their many-body effects, underpinning new possibilities for developing optoelectronic devices based on transport properties of a single type of carrier.