The study of estimation method of broadband emissivity from EOS/MODIS data

The broadband emissivity is an important parameter for estimating the energy balance of the Earth. This study focuses on estimating the window （8 -12 μm） emissivity from the MODIS （mod- erate-resolution imaging spectroradiometer） data, and two methods are built. The regression method obtains the broadband emissivity from MODllB1 - 5KM product, whose coefficient is developed by using 128 spectra, and the standard deviation of error is about 0.0118 and the mean error is about O. 0084. Although the estimation accuracy is very high while the broadband emissivity is estimated from the emissivity of bands 29, 31 and 32 obtained from MOD11B1 _ 5KM product, the standard deviations of errors of single emissivity in bands 29, 31, 32 are about 0.009 for MOD11B1 5KM product, so the total error is about O. 02 and resolution is about 5km × 5km. A combined radiative transfer model with dynamic learning neural network method is used to estimate the broadband emis- sivity from MODIS 1B data. The standard deviation of error is about 0.016, the mean error is about 0.01, and the resolution is about 1 km x 1 km. The validation and application analysis indicates that the regression is simpler and more practical, and estimation accuracy of the dynamic learning neural network method is higher. Considering the needs for accuracy and practicalities in application, one of them can be chosen to estimate the broadband emissivity from MODIS data.

Field validation of the GLASS land surface broadband emissivitydatabase using pseudo-invariant sand dune sites in northern China

The land surface broadband emissivity (LSBE) is a key parameter for estimatingsurface radiation, and there have been many studies of the LSBE at global orlocal scales. However, few studies have validated the surface emissivity databasewith multi-point field measurement data using infrared radiometry, especially inChina. In this study, we focus on the validation of the emissivity product of theglobal land surface satellite (GLASS) LSBE database for northern China for theperiod from 2006 to 2011. Specifically, we have employed an eight-day averaged,gridded emissivity product in the 813.5 mm spectral range produced at a spatialresolution of 1000 m from the Moderate Resolution Imaging Spectrometeralbedo product using a new algorithm. The GLASS LSBE database was validatedover bare surfaces with field measurement data from sand samples collected atmany pseudo-invariant sand dune sites located in western and northwesternChina. By comparing measured emissivity for different land surface types atdifferent sites and different times, it was shown that the results were consistentand that the accuracy of the field measurements was reliable. The results of thevalidation of GLASS LSBE with these field emissivity data showed very goodagreement.

Integrating ASTER and GLASS broadband emissivity products using a multi-resolution Kalman filter

In this study,the multi-resolution Kalman filter(MKF)algorithm,which can handle multi-resolution problems with high computational efficiency,was used to blend two emissivity products:the Global LAnd Surface Satellite(GLASS)(BBE)product and the Advanced Spaceborne Thermal Emission and Reflection Radiometer(ASTER)narrowband emissivity(NBE)product.The ASTER NBE product was first converted into a BBE product.A new detrending method was used to transfer the BBEs into a process suitable for the MKF.The new detrending method was superior to the two existing methods.Finally,both the de-trended GLASS and ASTER BBE products were incorporated into the MKF framework to obtain the optimal estimation at each scale.Field measurements collected in North America were used to validate the integrated BBEs.Visually,the fusion map showed good continuity,with the exception of the border areas,and the quality of the fusion map was better than that of the original maps.The validation results indicate that the MKF improved the BBE product accuracy at the coarse scale.In addition,the MKF was capable of recovering missing pixels at a finer scale.

A disaggregation approach for estimating high spatial resolution broadband emissivity for bare soils from Landsat surface reflectance

High spatial resolution land surface broadband emissivity(BBE)is not only useful for surface energy balance studies at local scales,but also can bridge the gap between existing coarser resolution BBE products and point-based field measurements.This study proposes a disaggregation approach that utilizes the established BBE–reflectance relationship for estimating high spatial resolution BBE for bare soils from Landsat surface reflectance data.The disaggregated BBE is compared to the BBE calculated from spatial–temporal matched Advanced Spaceborne Thermal Emission and Reflectance Radiometer emissivity product.Comparison results show that better agreement is achieved over relative homogeneous areas,but deteriorated over heterogeneous and cloud-contaminated areas.In addition,field-measured emissivity data over large homogeneous desert were also used to validate the disaggregated BBE,and the bias is 0.005.The comparison and validation results indicated that the disaggregation approach can obtain high spatial resolution BBE with better accuracy for homogeneous area.

The dawn−dusk asymmetry in mesosphere and lower thermosphere temperature disturbances during geomagnetic storms at high latitude

Utilizing observations by the Sounding of the Atmosphere using Broadband Emission Radiometry(SABER)instrument,we quantitatively assessed the dawn-dusk asymmetry in temperature disturbances within the high-latitude mesosphere and lower thermosphere(MLT)during the main phase of geomagnetic storms in this study.An analysis of five geomagnetic superstorm events indicated that during the main phase,negative temperature disturbances were more prevalent on the dawn side than on the dusk side in the high-latitude MLT region.Results of a statistical analysis of 54 geomagnetic storm events also revealed a notable disparity in temperature disturbances between the dawn and dusk sides.At high latitudes,38.2%of the observational points on the dawn side exhibited negative temperature disturbances(less than−5 K),whereas on the dusk side,this percentage was only 29.5%.In contrast,at mid-latitudes,these proportions were 34.1%and 36.5%,respectively,showing no significant difference.We also conducted a statistical analysis of temperature disturbances at different altitudes,which revealed an increase in the proportion of warming disturbances with altitude.Conversely,the proportion of cooling disturbances initially rose with altitude,reaching a peak around 105 km,and subsequently decreased.These temperature disturbance differences could be explained by the day-night asymmetry in vertical wind disturbances during storm conditions.

A Temperature-Insensitive Amplified Spontaneous Emission Broadband Source Based on Er-Doped Fiber

To obtain a stable amplified spontaneous emission（ASE） source for complex environment applications, we design an ASE source and study the output power and spectral characteristics under different ambient temperatures.We optimize the structure of the ASE source to flatten the ASE spectrum, and study the output characteristics in terms of output power and optical spectrum under different pump powers. Then the performance of the ASE source is investigated in the temperature range from-18.9°C to 50°C. A stable-power and flat-spectrum ASE source can be obtained by structural optimization and pump control.

Achieving broadband near-infrared luminescence in Cr^(3+)-Activated Y_(2)Mg_(2)Al_(2)Si_(2)O_(12)phosphors via multi-site occupancy

Cr^(3+)-activated near-infrared(NIR)phosphors are key for NIR phosphor-converted light emitting diodes(NIR pc-LED).While,the site occupancy of Cr^(3+)is one of the debates that have plagued researchers.Herein,Y2Mg2Al2-Si_(2)O1_(2)(YMAS)with multiple cationic sites is chosen as host of Cr^(3+)to synthesize YMAS:xCr^(3+)phosphors.In YMAS,Cr^(3+)ions occupy simultaneously Al/SiO4 tetrahedral,Mg/AlO6 octahedral,and Y/MgO8 dodecahedral sites which form three luminescent centers named as Cr1,Cr2,and Cr3,respectively.Cr1 and Cr2 relate to an intermediate crystal field,with transitions of^(2)E→^(4)A_(2)and^(4)T_(2)→^(4)A_(2)occurring simultaneously.As Cr^(3+)concentration increases,the^(4)T_(2)→^(4)A_(2)transition becomes more pronounced in Cr1 and Cr2,resulting in a red-shift and broadband emission.Cr3 consistently behaves a weak crystal field and exhibits the broad and long-wavelength emission.Wide-range NIR emission centering at 745 nm is realized in YMAS:0.03Cr^(3+)phosphor.This phosphor has high internal quantum efficiency(IQE?86%)and satisfying luminescence thermal stability(I423 K?70.2%).Using this phosphor,NIR pc-LEDs with 56.6 mW@320 mA optical output power is packaged and applied.Present study not only demonstrates the Cr^(3+)multi-site occupancy in a certain oxide but also provides a reliable approach via choosing a host with diverse cationic sites and local environments for Cr^(3+)to achieve broadband NIR phosphors.

Estimating global land surface broadband thermal-infrared emissivityusing advanced very high resolution radiometer optical data

An algorithm for retrieving global eight-day 5 km broadband emissivity (BBE)from advanced very high resolution radiometer (AVHRR) visible and nearinfrared data from 1981 through 1999 was presented. Land surface was dividedinto three types according to its normalized difference vegetation index (NDVI)values: bare soil, vegetated area, and transition zone. For each type, BBE at813.5 mm was formulated as a nonlinear function of AVHRR reflectance forChannels 1 and 2. Given difficulties in validating coarse emissivity products withground measurements, the algorithm was cross-validated by comparing retrievedBBE with BBE derived through different methods. Retrieved BBE was initiallycompared with BBE derived from moderate-resolution imaging spectroradiometer (MODIS) albedos. Respective absolute bias and root-mean-square errorwere less than 0.003 and 0.014 for bare soil, less than 0.002 and 0.011 fortransition zones, and 0.002 and 0.005 for vegetated areas. Retrieved BBE wasalso compared with BBE obtained through the NDVI threshold method. Theproposed algorithm was better than the NDVI threshold method, particularly forbare soil. Finally, retrieved BBE and BBE derived from MODIS data wereconsistent, as were the two BBE values.

Crystal Growth,Spectroscopic Properties and Energy Levels of Cr^(3+):Li_2Mg_2(MoO_4)_3

This paper reported the crystal growth and spectroscopy characters of Cr^3＋：Li2Mg2（MoO4）3. The refractive index of Cr^3＋：Li2Mg2（MoO4）3 crystal is 1.87 and the hardness is 270 I-IV. This crystal shows broadband absorption property with peak wavelength at about 495 and 699 nm. The absorption crosssection is 14.75 × 10^-20 cm^2 at 495 nm and 9.63 ×10^-20 cm^2 at 699 nm, respectively. The crystal field strength and energy levels of Cr^3＋ ion were calculated based on the spectroscopic data. The Cr^3＋：Li2Mg2（MoO4）3 crystal shows broadband emission extending from 750 to 1300 nm even excited at 10 K. The room temperature emission cross section is 72×10^-20 cm^2 at 926 nm. A discussion of the relation between the spectroscopic properties and crystal field parameters of Cr^3＋：Li2Mg2（MoO4）3 crystal was presented based on the solid state spectroscopytheory.

发射峰为875 nm的高热稳定性立方相Sc(PO_(3))_(3):Cr^(3+)荧光粉

近红外(NIR)荧光粉转换型发光二极管(pc-LED)具有尺寸小、效率高以及光谱易于调节的特点,在特种照明、传感、微型近红外光谱仪等各领域有很好的应用前景.目前,已报道的发射波长超过850 nm的近红外荧光粉的荧光热稳定性较差.在本项研究中,我们合成了一种立方相结构的Sc(PO_(3))_(3):xCr^(3+)(x=0,1,5,10,12,14,16,18 at%)荧光粉,其具有725–1150 nm的宽发射带,发射峰为875 nm,与之前报道的发射峰超过850 nm的荧光粉相比,其表现出优异的热稳定性,在423 K下,5 at%样品的积分发光强度保留了室温下的73.4%.通过对比研究立方相和单斜相Sc(PO_(3))_(3):Cr^(3+)荧光粉变温X射线衍射,发现立方相荧光粉优异的荧光热稳定性可能归因于高温下较小的键长和键角变化.利用该荧光粉制备的NIR pc-LED在150 mA电流驱动下,产生了26.62 mW的NIR辐射功率.驱动电流为10 mA时,最高电光转换效率为11.87%.这项工作为开发具有优异荧光热稳定性的Cr^(3+)离子掺杂近红外荧光粉提供了思路.

Development of Bi/Er co-doped optical fibers for ultra-broadband photonic applications

Targeting the huge unused bandwidth（BW）of modem telecommunication networks,Bi/Er co-doped silica optical fibers（BEDFs）have been proposed and developed for ultra-broadband,high-gain optical amplifiers covering the 1150-1700 nm wavelength range.Ultrabroadband luminescence has been demonstrated in both BEDFs and bismuth/erbium/ytterbium co-doped optical fibers（BEYDFs）fabricated with the modified chemical vapor deposition（MCVD）and in situ doping techniques.Several novel and sophisticated techniques have been developed for the fabrication and characterization of the new active fibers.For controlling the performance of the active fibers,post-treatment processes using high temperature,γ-radiation,and laser light have been introduced.Although many fundamental scientific and technological issues and challenges still remain,several photonic applications,such as fiber sensing,fiber gratings,fiber amplification,fiber lasers,etc.,have already been demonstrated.

PbS quantum dots and Ba F_(2):Tm^(3+) nanocrystals co-doped glass for ultra-broadband near-infrared emission [Invited]

With the rapid growth of optical communications traffic,the demand for broadband optical amplifiers continues to increase.It is necessary to develop a gain medium that covers more optical communication bands.We precipitated PbS quantum dots(QDs) and Ba F_(2):Tm^(3+) nanocrystals (NCs) in the same glass to form two independent emission centers.The Ba F_(2)NCs in the glass can provide a crystal field environment with low phonon energy for rare earth (RE) ions and prevent the energy transfer between RE ions and PbS QDs.By adjusting the heat treatment schedule,the emission of the two luminescence centers from PbS QDs and Tm^(3+) ions perfectly splices and covers the ultra-broadband near-infrared emission from 1200 nm to 2000 nm with bandwidth over 430 nm.Therefore,it is expected to be a promising broadband gain medium for fiber amplifiers.

Two SbX_(5)-based isostructural polar 1D hybrid antimony halides with tunable broadband emission,nonlinear optics,and semiconductor properties

Metal halide perovskites based on MX6(M is metal and X is halogen)octahedra have developed into significant materials,extensively used in many fields,such as solid-state lighting,semiconductor,and nonlinear optics.However,the MX_(5)square pyramid-based hybrid metal halides beyond zero-dimensional(0D)polyhedrons and clusters are rarely reported.Herein,we reported two new isostructural hybrid antimony halides,namely(2cepyH)SbCl4(1-Cl)and(2cepyH)SbBr4(2-Br)(2cepy=1-(2-chloroethyl)pyrrolidine),characterized by 1D polar polyanionic chains formed by corner-sharing SbX_(5)tetragonal pyramid units.Upon photoexcitation at 340 nm,1-Cl shows broad,yellow phosphorescence emissions stemming from triplet self-trapped excitons,as proved by its long lifetime(6.85μs)and the temperature dependences of broadband emission.To our knowledge,this should be the first observation on the broadband emissive properties in the 1D hybrid metal halide constructed by MX_(5)tetragonal pyramid units.Moreover,second harmonic generation measurements show that the nonlinear optical properties of 2-Br(∼3.2×KDP)are superior to that of 1-Cl(∼1.8×KDP).Experimental and calculated data indicate that the bandgap of 1-Cl is larger than that of 2-Br and that the polar inorganic moieties determine their band structures.Our work opens up a new way for constructing broadband emission materials with novel polar frameworks.

Broadband 1.5-um emission of erbium-doped TeO_2-WO_3-Nb_2O_5 glass for potential WDM amplifier

Erbium-doped glass showing the wider 1.5-um emission band is reported in a novel oxide system TeO2-WO3-Nb2O5 and their thermal stability and optical properties such as absorption, emission spectra, cross-sections and fluorescence lifetime were investigated. Compared with other glass hosts, the gain bandwidth properties of Er3+ in TWN glass is close to that of bismuth glasses, and larger than those of tellurite, germanate, silicate and phosphate glasses. The broad and flat 4I13/2-4I15/2 emission and the large stimulated emission cross-section of Er3+ ions around 1.5um can be used as host material for potential broadband optical amplifier in the wavelength-division-multiplexing (WDM) network system.

Self-trapped excitons in two-dimensional perovskites

With strong electron-phonon coupling,the self-trapped excitons are usually formed in materials,which leads to the local lattice distortion and localized excitons.The self-trapping strongly depends on the dimensionality of the materials.In the three dimensional case,there is a potential barrier for self-trapping,whereas no such barrier is present for quasi-one-dimensional systems.Two-dimensional(2D)systems are marginal cases with a much lower potential barrier or nonex istent potential barrier for the self-trapping,leading to the easier formation of self-trapped states.Self-trapped excitons emission exhibits a broadband emission with a large Stokes shift below the bandgap.2D perovskites are a class of layered structure material with unique optical properties and would find potential promising optoelectronic.In particular,self-trapped excitons are present in 2D per-ovskites and can significantly influence the optical and electrical properties of 2D perovskites due to the soft characteristic and strong electron-phonon interaction.Here,we summarized the luminescence characteristics,origins,and characterizations of self-trapped excitons in 2D perovskites and finally gave an introduction to their applications in optoelectronics.

Highly Efficient Self-Trapped Bluish White-Light Emission from[Pb4Cl5]3+Nodes in a Moisture-Tolerant Metal–Organic Framework

Highly luminescent zero-dimensional(0D)metal halide clusters attract widespread attention owing to strong exciton confinement and populated self-trapped states but often exhibit narrow emission and are susceptible to hydrolysis.Herein,we demonstrate a moisture-resistant metal–organic framework(MOF)consisting of cationic 0D[Pb_(4)Cl_(5)]^(3+)nodes bridged by adamantanetetracarboxylate.Upon near-UV excitation,the material emits intrinsic broadband bluish white-light emission with high external quantum efficiency of 35%and a color rendering index of 76.Unlike organoammonium cations in lead perovskites,the Pb-carboxylate coordination affords the MOF to be chemically stable and photostable in high humidity.The photoemitter exhibits undiminished photoemissions under ambient conditions[∼60%relative humidity(RH)]upon continuous UV irradiation(143 mW/cm^(2),365 nm)for 7 days.The insertion of[Na_(4)Cl]^(3+)moieties will connect 0D units into two-dimensional(2D)metal halide layers to limit structural strain and decrease the quantum efficiency from 35%to 15%,confirming the key importance of 0D units for efficient emission.