Improving the UV-light stability of silicon heterojunction solar cells through plasmon-enhanced luminescence downshifting of YVO_(4):Eu^(3+),Bi^(3+)nanophosphors decorated with Ag nanoparticles

The ultraviolet(UV)light stability of silicon heterojunction(SHJ)solar cells should be addressed before large-scale production and applications.Introducing downshifting(DS)nanophosphors on top of solar cells that can convert UV light to visible light may reduce UV-induced degradation(UVID)without sacrificing the power conversion efficiency(PCE).Herein,a novel composite DS nanomaterial composed of YVO_(4):Eu^(3+),Bi^(3+)nanoparticles(NPs)and AgNPs was synthesized and introduced onto the incident light side of industrial SHJ solar cells to achieve UV shielding.The YVO_(4):Eu^(3+),Bi^(3+)NPs and Ag NPs were synthesized via a sol-gel method and a wet chemical reduction method,respectively.Then,a composite structure of the YVO_(4):Eu^(3+),Bi^(3+)NPs decorated with Ag NPs was synthesized by an ultrasonic method.The emission intensities of the YVO_(4):Eu^(3+),Bi^(3+)nanophosphors were significantly enhanced upon decoration with an appropriate amount of~20 nm Ag NPs due to the localized surface plasmon resonance(LSPR)effect.Upon the introduction of LSPR-enhanced downshifting,the SHJ solar cells exhibited an~0.54%relative decrease in PCE degradation under UV irradiation with a cumulative dose of 45 k W h compared to their counterparts,suggesting excellent potential for application in UV-light stability enhancement of solar cells or modules.

Lanthanide-based downshifting layers tested in a solar car race

The mismatch between the AM1.5G spectrum and the photovoltaic (PV) cells absorption is one of the most limiting factors for PV performance.To overcome this constraint through the enhancement of solar energy harvesting,luminescent downshifting (LDS) layers are very promising to shape the incident sunlight and,thus,we report here the use of Tb^3+- and Eu^3+-doped organic-inorganic hybrid materials as LDS layers on Si PV cells.Electrical measurements on the PV cell,done before and after the deposition of the LDS layers,confirm the positive effect of the coatings on the cell’s performance in the UV spectral region.The maximum delivered power and the maximum absolute external quantum efficiency increased 14% and 27%,respectively.Moreover,a solar powered car race was organized in which the small vehicle containing the coated PV cells presented a relative increase of 9% in the velocity,when compared to that with the uncoated one.

ZnSe quantum dots downshifting layer for perovskite solar cells

To date, the instability of organometal halide perovskite solar cells（PSCs） has become the focus issue that limits the development and long-term application of PSCs. Both the ultraviolet（UV） rays in sunlight and moisture in air can significantly accelerate the disintegration of the perovskite. Here, we introduced a Zn Se quantum dots layer as downshifting materials, which was spin-coated onto the backside of PSCs.This layer converted the UV rays into visible light to prevent the destruction of PSCs as well as increase the light harvesting of the perovskite layer. Under the UV irradiation in the moisture ambient（40%）, the destruction speed of the unencapsulated perovskite films were also delayed evidently. In addition, the power conversion efficiency（PCE） of the PSCs was increased from 16.6% to 17.3% due to the increase of the visible light absorbance of the perovskite.

On the Downshift of Wave Frequency for Bragg Resonance

For surface gravity waves propagating over a horizontal bottom that consists of a patch of sinusoidal ripples,strong wave reflection occurs under the Bragg resonance condition.The critical wave frequency,at which the peak reflection coefficient is obtained,has been observed in both physical experiments and direct numerical simulations to be downshifted from the well-known theoretical prediction.It has long been speculated that the downshift may be attributed to higher-order rippled bottom and free-surface boundary effects,but the intrinsic mechanism remains unclear.By a regular perturbation analysis,we derive the theoretical solution of frequency downshift due to third-order nonlinear effects of both bottom and free-surface boundaries.It is found that the bottom nonlinearity plays the dominant role in frequency downshift while the free-surface nonlinearity actually causes frequency upshift.The frequency downshift/upshift has a quadratic dependence in the bottom/free-surface steepness.Polychromatic bottom leads to a larger frequency downshift relative to the monochromatic bottom.In addition,direct numerical simulations based on the high-order spectral method are conducted to validate the present theory.The theoretical solution of frequency downshift compares well with the numerical simulations and available experimental data.

Microwave frequency downshift in the time-varying collision plasma

Microwave frequency downshift in the time-varying collision plasma has been demonstrated by particle-in-cell simulations.The simulation results are consistent with the theoretical analysis,and the preconditions for microwave frequency downshift are that the collision frequency needs to be greater than the incident wave frequency,and the plasma frequency is two times greater than the incident wave frequency.Finally,the simulation results are compared with the reported experimental results indicating good agreement.

Emission colour tuning in KLnF_(4):Yb^(3+),Er^(3+)/Ho^(3+)phosphor

KLnF_(4):Yb^(3+),Er^(3+)/Ho^(3+)(Ln=Y,Yb,Gd)phosphors were prepared by solid-state reaction technique.For each of the Yb^(3+)/Er^(3+)and Yb^(3+)/Ho^(3+)co-doped phosphors independently,phase confirmation and morphological examination were accomplished using the X-ray diffraction technique and scanning electron microscope analysis.X-ray photoelectron spectroscopy analysis shows the charge state and existence of lanthanides and dopants.Upconversion luminescence emissions of green and red colour were detected for the synthesized phosphors.The changes in the upconverted emission intensities and colour output pertaining to the change of the lanthanide host matrix along with dopants were investigated for the prepared phosphors.In the upconversion luminescence,erbium-doped samples exhibit a predominance of red emission while holmium-doped samples display a prevalence of green emission.The rare-earth Er/Ho doped KYbF4shows strong red emission compared to other hosts.KYF_(4):Yb,Er/Ho exhibits relatively significant green upconve rsion emissions,while Yb,Er-doped KGdF_(4)host displays a 10-fold increase in green/red emission ratio with an increase in the input power of 20-780 mW.Downshifting photoluminescence studies and decay curve analysis were carried out using UV light excitation for the developed phosphors.A higher lifetime of 2.2 ms was measured for the downshifting red emission in the Ho doped KYbF_(4)sample.This study suggests a potential for colour tunability in the upconversion and downshifting emissions through host modifications to the fluoride phosphor.

"Chameleon-like" optical behavior of lanthanide-doped fluoride nanoplates for multilevel anti-counterfeiting applications

Lanthanide-based luminescent anti-counterfeiting materials are widely used in various kinds of products.However,the emission color of traditional lanthanide-based luminescent materials usually remains nearly unaltered upon different excitation lights,which may only work for single-level anti-counterfeiting.Herein,the NaYbF4∶2%Er@NaYF4 core/shell nanoplates (NPs) with "chameleon-like" optical behavior are developed.These NPs display single-band red or green downshifting (DS) emission upon excitation at 377 or 490 nm,respectively.Upon 980 nm excitation,the color of upconversion (UC) emission can be finely tuned from green to yellow,and to red with increasing the excitation power density from 0.1 to 4.0 W/cm^2.The proposed materials readily integrate the advantages of excitation wavelength-dependent DS single-band emissions and sensitive excitation power-dependent UC multicolor emissions in one and the same material,which has never been reported before.Particularly,the proposed NPs exhibit excellent performance as security labels on trademark tag and security ink on painting,thus revealing the great potential of these lanthanide-doped fluoride NPs in multilevel anti-counterfeiting applications.

Emissions of Er3+ and Yb3+ co-doped SrZrO3 nanocrystals under near-infrared and near-ultraviolet excitations

In this study,the upconversion(UC)emissions of Er3+and Yb3+co-doped SrZrO3 nanocrystals(NCs)were investigated in terms of the thermal annealing temperature and concentration of Er3+ions and compared with the emissions under a near-ultraviolet(near-UV)excitation.The NCs were synthesized by the combustion method,and the as-synthesized NCs were post-annealed at high temperatures.The X-ray diffraction patterns revealed that the grain sizes and crystallinity degrees of the samples increased with increasing annealing temperatures.The photoluminescence spectra of our samples exhibited strong green and very weak red emissions with the near-UV excitation,originating from the f-f transitions in the Er3+ions.Interestingly,under near-infrared(near-IR)excitation,we identified sizable visible emissions at 525,547,and 660 nm in our NCs,which indicated that the UC process successfully occurred in our NCs.These UC emissions were maximized in the NCs with an Er3+concentration of 0.02 and thermal annealing at 1000°C.We found that the intensity ratios of red to green emissions increased with increasing annealing temperatures.We discussed the differences in the emissions between near-UV and near-IR excitations.

In vivo optical bioimaging by using Nd-doped LaF3 luminescent nanorods in the second near-infrared window

Fluorescent imaging in the second near-infrared(NIR-Ⅱ,1000-1700 nm)region has attracted enormous research interest due to its advantages of unprecedentedly improved imaging sensitivity and spatial resolution.Herein,high quality NIR-Ⅱemissive LaF3:Nd3+nanorods(NRs)with hexagonal phase structure and controlled size were synthesized by a hydrothermal method.And the Nd^3+doping induced NIRⅡluminescent intensity evolution was studied,In vivo NIR-Ⅱbioimaging and real-time tracking reveal that these LaF3:Nd^3+NRs are mainly accumulated in liver and spleen.Moreover,in vivo toxicity assessment demonstrates that LaF3:Nd^3+NRs feature low biotoxicity and good biocompatibility in living animals.Therefore,the NIR-Ⅱemitting hexagonal phase LaF3 NRs with controlled size are promising probes for optical bioimaging.

Governing of down-shifting processes in LiLaP_4O_(12):Tb^(3+),Yb^(3+) for enhancement of its near-infrared emission

Downshifting behavior of the Tb3＋-gb3＋ co-doped nanocrystalline LiLaP4012 powders synthesized by co-precipitation method was presented and discussed. The structural phase purity of obtained material was confirmed by X-ray diffraction （XRD） measurements. Strong enhancement of ytterbium 2 2 - 3＋ F5/2- F7/2 emission intensity was observed with decreasing Tb concentration un- der UV excitation. Dependence of efficiency of energy transfer between dopants on pumping wavelength was investigated due to bet- ter understanding of down-shifting mechanism. It was found that luminescence intensity of Yb3＋ decreased above 10 tool.% dopant con- tent, what was caused by concentration quenching. The power dependence measurements were carried out at 77 and 300 K. The re- sulting slopes had the same value of 1, what indicated the existence of linear down-shifting process, independent of the temperature.

MPC-Based Downshift Control of Automated Manual Transmissions

Automated manual transmissions,which usually adopt synchronizers to complete the gear shift process,have many advantageous features.However,the torque interruption and the challenging control objectives during the gear shift process limit its industrial application,especially for the power-on gear downshift.This paper proposes a model predic-tive control(MPC)method to control the clutch engagement process and effectively shorten the torque interruption,consequently enhancing the gear downshift quality.During the control law deduction,the proposed MPC also accounts for time-domain constraints explicitly.After the control law was deduced,it was validated through simulations under two typical power-on gear downshift working scenarios.Both of the simulation results demonstrate that the controller proposed in this paper can shorten the torque interruption time during power-on gear downshifts while minimizing vehicle jerk for overall satisfactory drivability.