Ultrahigh performance passive radiative cooling by hybrid polar dielectric metasurface thermal emitters

Real-world passive radiative cooling requires highly emissive,selective,and omnidirectional thermal emitters to maintain the radiative cooler at a certain temperature below the ambient temperature while maximizing the net cooling power.Despite various selective thermal emitters have been demonstrated,it is still challenging to achieve these conditions sim-ultaneously because of the extreme difficulty in controlling thermal emission of photonic structures in multidimension.Here we demonstrated hybrid polar dielectric metasurface thermal emitters with machine learning inverse design,en-abling a high emissivity of~0.92 within the atmospheric transparency window 8-13μm,a large spectral selectivity of~1.8 and a wide emission angle up to 80 degrees,simultaneously.This selective and omnidirectional thermal emitter has led to a new record of temperature reduction as large as~15.4°C under strong solar irradiation of~800 W/m2,signific-antly surpassing the state-of-the-art results.The designed structures also show great potential in tackling the urban heat island effect,with modelling results suggesting a large energy saving and deployment area reduction.This research will make significant impact on passive radiative cooling,thermal energy photonics and tackling global climate change.

Phonon-assisted upconversion photoluminescence of quantum emitters

Quantum emitters are widely used in quantum networks,quantum information processing,and quantum sensing due to their excellent optical properties.Compared with Stokes excitation,quantum emitters under anti-Stokes excitation exhibit better performance.In addition to laser cooling and nanoscale thermometry,anti-Stokes excitation can improve the coherence of single-photon sources for advanced quantum technologies.In this review,we follow the recent advances in phononassisted upconversion photoluminescence of quantum emitters and discuss the upconversion mechanisms,applications,and prospects for quantum emitters with anti-Stokes excitation.

Effects of arrangement of surge-root irrigation emitters on growth,yield and water use efficiency of apple trees

Six-year old apple trees were selected for field experiment.The objective of this study was to obtain the reasonable arrangement of surge-root irrigation emitters in apple orchards.There were three factors:the buried depth H(25,40,55 cm),the horizontal distance L(30,40,60 cm)between the emitters and the trunk of the experimental tree,and the number of the irrigation emitters N(1,2,4).The effect of the arrangement of surge-root irrigation emitters on the growth,yield and irrigation water use efficiency(IWUE)of apple trees were studied in Northern Shaanxi where the irrigation quota takes 60%-75%of the field water capacity.The results showed that the arrangement of emitters for surge-root irrigation had a significant effect on apple tree yield and IWUE,especially,the yield and IWUE reached 28388.17 kg/hm2 and 16.83 kg/m3 in treatment T3,respectively.At the same L and N levels(T1,T2,and T3),the yield and IWUE in treatment T3 were the highest,and the yields in treatments T1 and T2 were decreased by 26.22%and 31.48%,while IWUE is reduced by14.02%and 18.12%compared with T3,respectively.At the same H and N levels(T3,T4,and T5),the yield and IWUE of apple trees were decreased with increasing L level.Especially,when L was 30 cm(T3),the yield and IWUE were the highest.The same L and H levels(T3,T6,and T7)could promote the growth of apple trees when N was 2(T3).Compared with treatment T3,it was found that the increment of new shoots was decreased by 8.07%-18.71%,and the fruit diameter was decreased by 5.41%-9.11%.Therefore,two emitters should be arranged symmetrically on both sides of an apple tree,each was buried at a 40 cm depth and 30 cm away from the trunk of the tree to effectively improve the yield and IWUE of the apple tree in mountainous areas in Northern Shaanxi.

Comparing and evaluating the nationally determined contributions of the top six emitters under the Paris Agreement goals

Comparing and evaluating the Nationally Determined Contribution(NDC) is an important element in global stocktake in the post-Paris climate negotiations, aimed at closing the emissions gap with the Paris Agreement goals. To date, however, there has still been no explicit guideline or method. By applying emissions allowance allocated by 16 schemes as benchmarks, this paper tries to compare and evaluate the NDCs of the top six emitters, which jointly account for about 70% of the world's CO_2 emissions. Results show that the four developed countries' NDCs lack ambition with respect to most allocations under 2℃ and all under 1.5℃, indicating they need to substantially ratchet up their NDCs and lead elevating mitigation. Evaluating cumulative emissions is more likely to clarify the ambition and fairness of China's NDC. If considering cumulative emissions, China's NDC is aligned with the median of cumulative allowances under 2℃ and within the 1.5℃ range. The Paris Agreement invited the Parties to communicate the mid-century low emissions strategies. This paper also tries to explore the mid-century mitigation in the perspective of allocations, which might provide decision-makers with some useful information when envisaging the post-NDC mitigation.

Clinical use of bone-targeting radiopharmaceuticals with focus on alpha-emitters

Various single or multi-modality therapeutic options are available to treat pain of bone metastasis in patients with prostate cancer.Different radionuclides that emitβ-rays such as 153Samarium and 89Strontium and achieve palliation are commercially available.In contrast toβ-emitters,223Radium as a a-emitter has a short path-length.The advantage of the a-emitter is thus a highly localized biological effect that is caused by radiation induced DNA double-strand breaks and subsequent cell killing and/or limited effectiveness of cellular repair mechanisms.Due to the limited range of the a-particles the bone surface to red bone marrow dose ratio is also lower for 223Radium which is expressed in a lower myelotoxicity.The a emitter 223Radium dichloride is the first radiopharmaceutical that significantly prolongslife in castrate resistant prostate cancer patients with wide-spread bone metastatic disease.In a phaseⅢ,randomized,double-blind,placebo-controlled study 921patients with castration-resistant prostate cancer and bone metastases were randomly assigned.The analysis confirmed the 223Radium survival benefit compared to the placebo(median,14.9 mo vs 11.3 mo;P<0.001).In addition,the treatment results in pain palliation and thus,improved quality of life and a delay of skeletal related events.At the same time the toxicity profile of223Radium was favourable.Since May 2013,223Radium dichloride(Xofigo?)is approved by the US Food and Drug Administration.

Ⅲ–Ⅴ compounds as single photon emitters

Single-photon emitters (SPEs) are one of the key components in quantum information applications. The ideal SPEs emit a single photon or a photon-pair on demand, with high purity and distinguishability. SPEs can also be integrated in photonic circuits for scalable quantum communication and quantum computer systems. Quantum dots made from Ⅲ-Ⅴ compounds such as InGaAs or GaN have been found to be particularly attractive SPE sources due to their well studied optical performance and state of the art industrial flexibility in fabrication and integration. Here, we review the optical and optoelectronic properties and growth methods of general SPEs. Subsequently, a brief summary of the latest advantages in Ⅲ-Ⅴ compound SPEs and the research progress achieved in the past few years will be discussed. We finally describe frontier challenges and conclude with the latest SPE fabrication science and technology that can open new possibilities for quantum information applications.

Brightening single-photon emitters by combining an ultrathin metallic antenna and a silicon quasi-BIC antenna

Bright single-photon emitters(SPEs)are fundamental components in many quantum applications.However,it is difficult to simultaneously get large Purcell enhancements and quantum yields in metallic nanostructures because of the huge losses in the metallic nanostructures.Herein,we propose to combine an ultrathin metallic bowtie antenna with a silicon antenna above a metallic substrate to simultaneously get large Purcell enhancements,quantum yields,and collection efficiencies.As a result,the brightness of SPEs in the hybrid nanostructure is greatly increased.Due to the deep subwavelength field confinement(mode size<10 nm)of surface plasmons in the ultrathin metallic film(thickness<4 nm),the Purcell enhancement of the metallic bowtie antenna improves by more than 25 times when the metal thickness decreases from 20 nm to 2 nm.In the hybrid nanostructures by combining an ultrathin metallic bowtie antenna with a silicon antenna,the Purcell enhancement(Fp≈2.6×10^(6))in the hybrid nanostructures is 63 times greater than those(≤4.1×10^(4))in the previous metallic and hybrid nanostructures.Because of the reduced ratio of electromagnetic fields in the ultrathin metallic bowtie antenna when the high-index silicon antenna is under the quasi-BIC state,a high quantum yield(QY≈0.70)is obtained.Moreover,the good radiation directivity of the quasi-BIC(bound state in the continuum)mode of the silicon antenna and the reflection of the metallic substrate result in a high collection efficiency(CE≈0.71).Consequently,the overall enhancement factor of brightness of a SPE in the hybrid nanostructure is EF∗≈Fp×QY×CE≈1.3×10^(6),which is 5.6×10^(2) times greater than those(EF∗≤2.2×103)in the previous metallic and hybrid nanostructures.

Platinum complexes as phosphorescent emitters in highly efficient organic light-emitting diodes

Applications of platinum complexes as phosphorescent emitters in high efficiency organic light-emitting diodes （OLEDs） were shortly discussed in this paper. Key recent studies on highly efficient blue, green, red and white-phosphorescent OLEDs based on Pt complexes are presented in terms of efficiency and color quality.

Polarization-switchable plasmonic emitters based on laser-induced bubbles

Owing to weak light-matter interactions in natural materials,it is difficult to dynamically tune and switch emission polariza-tion states of plasmonic emitters(or antennas)at nanometer scales.Here,by using a control laser beam to induce a bubble(n=1.0)in water(n=1.333)to obtain a large index variation as high as|Δn|=0.333,the emission polarization of an ultra-small plasmonic emitter(~0.4λ^(2))is experimentally switched at nanometer scales.The plasmonic emitter consists of two orthogonal subwavelength metallic nanogroove antennas on a metal surface,and the separation of the two anten-nas is only s_(x)=120 nm.The emission polarization state of the plasmonic emitter is related to the phase difference between the emission light from the two antennas.Because of a large refractive index variation(|Δn|=0.333),the phase difference is greatly changed when a microbubble emerges in water under a low-intensity control laser.As a result,the emission polarization of the ultra-small plasmonic emitter is dynamically switched from an elliptical polarization state to a linear polarization state,and the change of the degree of linear polarization is as high asΔγ≈0.66.

Photon pair source via two coupling single quantum emitters

We study the two coupling two-level single molecules driven by an external field as a photon pair source. The probability of emitting two photons, P2, is employed to describe the photon pair source quality in a short time, and the correlation coefficient RAB is employed to describe the photon pair source quality in a long time limit. The results demonstrate that the coupling single quantum emitters can be considered as a stable photon pair source.

Biofilm structure and its influence on clogging in drip irrigation emitters distributing reclaimed wastewater

Using reclaimed wastewater for crop irrigation is a practical alternative to discharge wastewater treatment plant effluents into surface waters.However,biofouling has been identified as a major contributor to emitter clogging in drip irrigation systems distributing reclaimed wastewater.Little is known about the biofilm structure and its influence on clogging in the drip emitter flow path.This study was first to investigate the microbial characteristics of mature biofilms present in the emitters and the effect of flow path structures on the biofilm microbial communities.The analysis of biofilm matrix structure using a scanning electron microscopy（SEM） revealed that particles in the matrix of the biofilm coupled extracellular polysaccharides（EPS） and formed sediment in the emitter flow path.Analysis of biofilm mass including protein,polysaccharide,and phospholipid fatty acids（PLFAs） showed that emitter flow path style influenced biofilm community structure and diversity.The correlations of biofilm biomass and discharge reduction after 360 h irrigation were computed and suggest that PFLAs provide the best correlation coeffcient.Comparatively,the emitter with the unsymmetrical dentate structure and shorter flow path（Emitter C） had the best anti-clogging capability.By optimizing the dentate structure,the internal flow pattern within the flow path could be enhanced as an important method to control the biofilm within emitter flow path.This study established electron microscope techniques and biochemical microbial analysis methods that may provide a framework for future emitter biofilm studies.

Improving reverse intersystem crossing of MR-TADF emitters for OLEDs

Thermally activated delayed fluorescence(TADF)emitter is a promising organic light-emitting diode(OLED)material due to low cost,wide luminous color gamut and 100%exciton utilization efficiency[1].To achieve high TADF performance,a feasible strategy is to construct a twisted donor–acceptor(D–A)unit,decreasing the overlap between the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO),and minimizing the energy gap(∆E_(ST))between the lowest singlet(S_(1))and triplet(T_(1))states[2,3].However,this long-range charge transfer feature is often disadvantageous for achieving high oscillator strengths(f)and radiative transition rates(k_(r))[4](Fig.1(a)).

Status of Selective Emitters for p-Type c-Si Solar Cells

Crystalline silicon (c-Si) solar cells have the lion share in world PV market. Solar cells made from crystalline silicon have lower conversion efficiency, hence optimization of each process steps are very important. Achieving low-cost photovoltaic energy in the coming years will depend on the development of third-generation solar cells. Given the trend towards these Si materials, the most promising selective emitter methods are identified to date. Current industrial monocrystalline Cz Si solar cells based on screen-printing technology for contact formation and homogeneous emitter have an efficiency potential of around 18.4%. Limitations at the rear side by the fully covering Al-BSF can be changed by selective emitter designs allowing a decoupling and separate optimization of the metallised and non-metallised areas. Several selective emitter concepts that are already in industrial mass production or close to it are presented, and their specialties and status concerning cell performance are demonstrated. Key issues that are considered here are the cost-effectiveness, added complexity, additional benefits, reliability and efficiency potential of each selective emitter tech- niques.

Thermophotovoltaic Emitters Based on a One-Dimensional Metallic-Dielectric Multilayer Nanostructures

In this paper, a one-dimensional multilayer is optimized for potential applications as thermophotovoltaic (TPV) selective emitter. The proposed TPV emitter was fabricated through a magnetron sputtering process by using the radio frequency (RF) magnetron sputtering system. The spectral emittance of the proposed TPV emitter is measured by using spectral transmittance and reflectance measurement system at wavelength from 0.3 μm to 2.5 μm at near-normal incident 8。. The bidirectional reflectance distribution function BRDF is measured by three axis automated scatterometer (TAAS). The effect of the diffraction orders and plane of incidence on the spectral emittance of the proposed TPV emitter is calculated numerically by using the rigorous coupled-wave analysis (RCWA). The emittance spectrum of the proposed TPV selective emitter shows three close to unity emission peaks which are explained by the surface plasmon polariton (SPP), gap plasmon polariton (GPP) and magnetic polariton (MP) excitation. The results show that the proposed emitter has high emittance value in the spectral range of 0.69 emitter, if used as a selective emitter with a low band gap photovoltaic cell (GaSb), would lead to high TPV overall efficiency and high electrical output power.

Epitaxial n- and p-type Emitters for High Efficiency Solar Cell Concepts

Reducing the module prices by increasing the efficiency of solar cells is one of the major challenges in today＇s photovoltaic research. The emitter formation by epitaxial growth offers a cost-efficient and faster alternative to the standard furnace diffusion process. The efficiency potential of epitaxial emitters 〉 22% has already been proven using a single wafer, low pressure, chemical vapour deposition tool. The purpose of this work is to show the potential of epitaxially grown emitters by APCVD （atmospheric pressure chemical vapour deposition） compared to diffused emitters. The APCVD formation of epitaxial emitters at 1,050 ~C can be realised as high throughput inline process and only takes 1-2 min, whereas the diffusion process using POCI3 takes up to 60 min. Simulations show an increase in voltage of AVoc = ＋10 mV and a reduction in saturation current ,1o of 30% for the epitaxial emitter. The lifetime experiments of solar cells with epitaxial emitter exhibit a diffusion length Leff〉 750μm and an emitter saturation current of Joe 〈 50 fA/cm2 on a planar 10 Ω2cm p-type FZ wafer. Another important aim of this work is to evaluate the limitations of epitaxial emitters due to high thermal budget, interface recombination and the change of reflective properties on textured wafers due to the deposition process. Solar cell efficiencies up to 18.4% on p-type and 20.0% on n-type wafers presented in this paper underline that the emitter epitaxy by APCVD is a competitive process for the emitter formation.

Escape probability for isotropic emitters near Kerr black hole with astrometric

The paper investigates the escape probability for isotropic emitters near a Kerr black hole.We propose a new approach to obtain the escape probability in a general manner,going beyond previous case-by-case studies.This approach is based on studies of the black hole shadow with astrometric observable and can be applied to emitters with an arbitrary 4-velocities and locations,even to the emitters outside of the equatorial plane.We also consider representative examples illustrating how escape probabilities vary with distance,velocity,and inclination angle.Overall,this new approach provides an effective method for studying escape probabilities near Kerr black holes.

Vibronic coupling effect on intersystem crossing rates of TADF emitters

To take advantage of all the singlet and triplet excitons and then achieve 100%internal quantum efficiency in OLED devices,the scientists have proposed the thermally activated delayed fluorescence(TADF)strategy which tries to achieve"delayed"fluorescence by converting triplet excitons to singlet excitons through a reverse intersystem crossing(ISC/RISC)process with the help of thermal activation[1].In the early days,the efficient RISC processes were facilitated by a negligible energy gap(△E_(ST))and a large spin-orbit coupling(SOC)matrix element(SOCME)between the first singlet(S_(1))and triplet(T_(1))excited states.

Constructing multifunctional deep-blue emitters with weak charge transfer excited state for high-performance non-doped blue OLEDs and single-emissive-layer hybrid white OLEDs

Deep-blue emitter with high photoluminescence efficiency(PLQY)is highly desirable in ultra-high definition displays and white solid-state lightings.In this work,two deep-blue phenanthro[9,10]imidazole derivatives,PPIS and PPPIS,with hot exciton property are successfully developed.Compared to PPIS,the embedded phenyl bridge in PPPIS is able to effectively increase the overlap of frontier molecular orbitals.In consequence,PPPIS shows higher oscillator strength and significantly enhanced PLQY.PPPIS also achieves better electroluminescence performance in non-doped device,showing deep-blue emission with Commission International de l’Eclairage(CIE)coordinates of(0.153,0.087)and the maximum external quantum efficiency(EQEmax)of 8.5%with minuscule efficiency roll-off.Meanwhile,when PPPIS serves as the host for phosphor PO-01,high-efficiency orange phosphorescent device is obtained with high EQEmax of 29.8%and negligible efficiency roll-off at 1000 cd/m^(2).Further,efficient single-emissive-layer white device is assembled via utilizing PPPIS as a blue emitter as well as the host for PO-01 simultaneously,providing warm-white emission with CIE coordinates of(0.429,0.433)at 1000 cd/m^(2),the forward-viewing EQEmaxof 27.2%and maximum power efficiency(PEmax)of 80.1 lm/W,respectively.Our studies can establish a viable design strategy for deep-blue emitters in high-performance non-doped blue OLEDs and hybrid WOLEDs.

Multiband metamaterial emitters for infrared and laser compatible stealth with thermal management based on dissipative dielectrics

The modulation of thermal radiation in the infrared region is a highly anticipated method to achieve infrared sensing and camouflage. Here, a multiband metamaterial emitter based on the Al∕SiO_(2)∕Al nanosandwich structure is proposed to provide new ideas for effective infrared and laser-compatible camouflage. By virtue of the intrinsic absorption and magnetic resonance property of lossy materials, the thermal radiation in the infrared region can be rationally modulated. The fabricated samples generally present low emissivity(ε_(3–5μm)= 0.21,ε_(8–14μm)= 0.19) in the atmospheric windows to evade infrared detection as well as high emissivity(ε_(5–8μm)= 0.43) in the undetected band for energy dissipation. Additionally, the laser camouflage is also realized by introducing a strong absorption at 10.6 μm through the nonlocalized plasmon resonance of the SiO_(2)layer.Moreover, the fabricated emitter shows promising prospects in thermal management due to the good radiative cooling property that is comparable to the metallic Al material. This work demonstrates a multiband emitter based on the metasurface structure with compatible infrared-laser camouflage as well as radiative cooling properties, which is expected to pave new routes for the design of thermal radiation devices.

Focus on perovskite emitters in blue light-emitting diodes

Blue perovskite light-emitting diodes(PeLEDs)are essential in pixels of perovskite displays,while their progress lags far behind their red and green counterparts.Here,we focus on recent advances of blue PeLEDs and systematically review the noteworthy strategies,which are categorized into compositional engineering,dimensional control,and size confinement,on optimizing microstructures,energy landscapes,and charge behaviors of wide-bandgap perovskite emitters(bandgap>2.5 eV).Moreover,the stability of perovskite blue emitters and related devices is discussed.In the end,we propose a technical roadmap for the fabrication of state-of-the-art blue PeLEDs to chase and achieve comparable performance with the other two primary-color devices.