Luminescence Properties of (Y, Gd)Al_3(BO_3)_4∶Eu ^(3+) under VUV excitation

Y, Gd)Al 3(BO 3) 4∶Eu 3+ samples were prepared by the conventional solid state reaction. The XRD results indicate that the crystal symmetry is low. The excitation spectrum is composed of two broad bands centered at about 170 and 250 nm respectively. In the emission spectra, the peak wavelength is about 616 nm under 147 nm VUV excitation. The luminescent chromaticity coordinate and the relative intensity change along with Gd 3+ mole concentration in the range of 0.15 to 0.85 mol (and Eu 3+ mole concentration, 0.02 to 0.1 mol). The correlative data show that the concentration quenching occurs when the Eu 3+ mole concentration ranges from 0.02 to 0.1 mol, and the Gd 3+→Gd 3+, Gd 3+→Eu 3+ and host→Eu 3+, Gd 3+ energy transfers exist, and Gd 3+ mole concentration influences Eu 3+ emission.

Synthesis, Composition Optimization, and VUV Photoluminescence Characterization of (Y,Gd)(V,P)O_4∶Eu^(3+) as A Potential Red-Emitting Plasma-Display Panel Phosphor

The synthesis, composition optimization, VUV Photoluminescence (PL) spectra, and optical properties, of (Y,Gd)(V,P)O4∶Eu3+ phosphors were investigated by synchrotron radiation. The VUV PLE spectra and the correlation among VUV PL intensity, λem, and Eu3+, Gd3+, and P-content were established. The PLE spectral studies showed that (Y,Gd)(V,P)O4∶Eu3+ exhibited significant absorption in the VUV range. The VUV PL intensity was found to enhance with PO43- and Gd3+-doping. Furthermore, the chromaticity characteristics of (Y,Gd)(V,P)O4∶Eu3+ were also found to be (0.6614, 0.3286) and compared against (Y, Gd)BO3∶Eu3+ as a reference. Based on the characterization results, we are currently improving and evaluating the potential application of (Y,Gd)(V,P)O4∶Eu3+ as a new red-emitting PDP phosphor.

Vacuum Ultraviolet Spectral Investigations on Green-Emitting Ca(La,Gd)_4Si_3O_(13):Tb^(3+) Phosphors for PDP Applications

In an effort to develop new green-emitting PDP phosphors with high efficiency, investigated were the synthesis, VUV photoluminescence (PL) spectra, optical properties, and chromaticity of Ca(La1-x-yTbxGdy. )4Si3O13 phosphors by using synchrotron radiation. Upon analysis of the VUV spectroscopic and chromaticity investigations on the new greenemitting VUV phosphors, were an optimized composition achieved. The PLE spectral studies show that Ca ( La1-x-y TbxGdy)4Si3O13 exhibit significant absorption in the VUV range. The VUV PL intensity was found to enhance with Gd3+-doping. Furthermore, the 1931 CIE chromaticity coordinates of Ca(La,Gd)4Si3O13:Tb were found to be (0.286, 0.548), as compared to (0.230, 0.712) for Zn2SiP4:Mn2+ as a reference. The potential application of Ca(La,Gd)4Si3O13:Tb as a new green-emitting PDP phosphor are being currently improving and evaluating.

White-light emission of ZnO nanoparticles prepared by sol-gel method

In：ZnO nanoparticles are prepared by the sol-gel process. The ratios of In/（Zn＋In） are 0%, 5%, 8%, 10%, and 15%, respectively. Crystal phase structures and optoelectronic properties of these samples are characterized and the chromaticity coordinates of different samples are also calculated in CIE-XYZ colour system. The results show that preferred growth direction of ZnO changes from （002） plane to （001） plane and interplanar distance becomes shorter. When the doping amount of In is 5%, Zn atoms are completely replaced by In atoms. The resistivities of the samples first decrease, then increase afterwards with the increase of the amount of In. With the increase of In, the ultraviolet emission is redshifted and new peaks occur at 465 nm, 535 nm, and 630 nm. The sample with 10% indium has white-light emission. The band structures of samples with 0% and 12.5% indium are investigated by the first principle method. The mechanism of white emission is discussed from the viewpoint of additional energy levels.

Establishment of a metric to characterize retroreflector properties using a consumer-grade colour camera

The coefficients of retroreflection and chromaticity coordinates are critical metrics for determining the quality of a retroreflector.However,conventional retroreflection measurement techniques rely heavily on the night-time colour,size and characteristics of thesample being measured.This complicates the measurement process and leads to deviations in the test results.In addition,chromaticitycannot be determined using this approach.Therefore,it is necessary to improve the measurement accuracy,simplify themeasurement process and achieve themeasurement of the traffic sign RA and chromaticity coordinates simultaneously.In this study,an improved method for retroreflector characterization using imaging was proposed.This allowed for the measurement of the coefficientsof retroreflection and the chromaticity coordinates simultaneously,and only a white standard sample was required for calibration.The primary components of the proposed system included a lighting projector,a receiver,two motorized rotational stages,a retroreflective sample holder and customized software that using scaling factors to convert a digital signal into sample retroreflectioncoefficients and retroreflective chromaticity coordinates.The experimental results indicated that the raw data output from thecamera exhibited a positive correlation relationship with the luminous flux from the surface of the retroreflector.The maximummeasurementerrors for the retroreflection and chromaticity were−12.2 cd/(lx·m2)and−2.09%,respectively.Thismethod was inexpensiveand convenient,used a commercially available digital camera,could help to identify defects in retroreflection and chromaticity forretroreflective sheeting and led to increased accessibility for the quality control of retroreflective sheeting.

Synthesis and luminescence properties of KCaPO_4:Eu^(2+),Tb^(3+),Mn^(2+) for white-light-emitting diodes(WLED)

In order to obtain a single-host white-light phosphor, a series of KCaPO4 powder samples tri-doped with Eu2＋, Tb3＋ and Mn2＋ were synthesized via high-temperature solid-state reaction method. Their structural and luminescence properties were investigated. Under proper ultraviolet excitation （255-405 urn）, white light was obtained, consisting of blue, green and red emissions stemming from Eu2＋, Th3＋, Mn2＋ ions respectively. The temperature stability of our sample was analyzed by studying the variation tendeney of CIE chromaticity coordinates at different temperatures. The results indicated that this phosphor could yield good color stability when utilized in WLED.

A novel fluorescent sensor for Al^(3+)and Zn^(2+)based on a new europium complex with a 1,10-phenanthroline ligand

A new europium complex Eu(tta)_(3)Li(la)based on 1,10-phenanthroline derivative(Li=(2-(3,5-dimethoxyphenyl)-1 H-imidazo[4,5-f][1,10]phenanthroline),tta=2-thenoyItrifluoroacetone)was designed and synthesized.Its structure was characterized by^(1)H and^(13)C NMR,elemental analysis,UV-vis,fluorescence spectra and single crystal X-ray diffraction.The crystal of the complex la belongs to monoclinic system with the space group P2_(1/n).The europium complex la in the solid and in the solution displays the typical emission of Eu(III)ion centered at 612 nm as a result of the electric dipole transition(^(5)D_(0)-►^(7)F_(2)).It exhibits high quantum yield(20.42%),long lifetime(0.29 ms)and good CIE color coordinate(0.67,0.33)in solid.In addition,the complex shows high sensitivity and selectivity towards Al^(3+)and Zn^(2+)in methanol solution which can be attributed to the Al^(3+)/Zn^(2+)cation instead of Eu^(3+)in the complex la.The LODs for Al^(3+)and Zn^(2+)were calculated to be 5.880×10^(-7)and 7.678×10^(-8)mol/L,respectively.Besides,the additions of Al^(3+)and Zn^(2+)express remarkable color changes from red to bright blue and ivory that can be clearly observed by the naked eye respectively.

Warm white emission of LaSr_(2)F_(7):Dy^(3+)/Eu^(3+)NPs with excellent thermal stability for indoor illumination

The novel single Dy^(3+)-activated and Dy^(3+)/Eu^(3+)co-activated LaSr_(2)F_(7) NPs-based phosphors were successfully synthesized via a simple precipitation reaction method at room temperature.The phase formations and cell parameters of single Dy^(3+)-activated and Dy^(3+)/Eu^(3+)co-activated LaSr_(2)F_(7) NPs were verified in detail by the Rietveld refinement technique based on the recorded X-ray diffraction patterns.The doping concentration of single Dy^(3+)-activated LaSr_(2)F_(7) NPs was optimized to be 0.1 mol with the concentration quenching dominated by the electric dipole-dipole interaction.Meanwhile,a variety of Eu^(3+)-activated La_(0.9)Sr_(2)F_(7):0.1Dy^(3+)NPs exhibited tunable luminescent properties and emitted warm white light in close to standard warm white light under 363 nm excitation.The valid energy transfer(ET)efficiency from Dy^(3+) to Eu^(3+) ions was estimated to be about 86.02%based on the emission intensity while the electric dipole-quadrupole interaction dominated the concentration quenching mechanism in ET process.Eventually,the thermal quenching of the obtained samples was studied,showing the excellent thermal stability.All the results manifest that Eu^(3+)-activated LaSr_(2)F_(7):Dy^(3+)NPs could emit warm white light with excellent thermal stability for indoor illumination.

Photophysical Performance and Energy Transfer Mechanism of a 1-D Chain-like Complex

By means of solvothermal reactions,a novel lanthanide-mercury compound,{[Ho(IA)3(H3O)2]2n[2n(HgCl4)][n(HgCl5)]}·3nH3O·nH2O(1,HIA=isonicotinc acid)was prepared and structurally characterized by single-crystal X-ray diffraction.Complex 1 crystallizes in the C2/c space group of monoclinic system with a=24.2147(5),b=20.8106(4),c=15.3060(3)Å,β=128.326(2)°,V=6050.8(2)Å3,C36H45Cl13Hg3Ho2N6O20,Mr=2274.26,Z=4,Dc=2.497 g/cm^3,μ(MoKα)=10.817 mm-1 and F(000)=4232.It exhibits a one-dimensional(1-D)chain-like structure.Solid-state photoluminescence measurement shows that it displays brown light emission bands.These emission bands originate from the characteristic emissions of the 4f electrons intrashell transitions of 5S2→5I8 and 5F5→5I8 of the holmium(Ⅲ)ions in 1.The photoluminescence emission energy transfer mechanism is elucidated by the energy level diagrams of the holmium(Ⅲ)ions and isonicotinic acid ligand.Complex 1 has CIE chromaticity coordinates of(0.4361,0.4992).Solid-state UV/Vis diffuse reflectance spectra reveal that it possesses wide optical band gap of 4.94 eV.

Greenness Index from Phenocams Performs Well in Linking Climatic Factors and Monitoring Grass Phenology in a Temperate Prairie Ecosystem

Near-surface remote sensing(e.g.,digital cameras)has played an important role in capturing plant phenological metrics at either a focal or landscape scale.Exploring the relationship of the digital image-based greenness index(e.g.,Gcc,green chromatic coordinate)with that derived from satellites is critical for land surface process research.Moreover,our understanding of how well Gcc time series associate with environmental variables at field stations in North American prairies remains limited.This paper investigated the response of grass Gcc to daily environmental factors in 2018,such as soil moisture(temperature),air temperature,and solar radiation.Thereafter,using a derivative-based phenology extraction method,we evaluated the correspondence between key phenological events(mainly including start,end and length of growing season,and date with maximum greenness value)derived from Gcc,MODIS and VIIRS NDVI(EVI)for the period 2015–2018.The results showed that daily Gcc was in good agreement with ground-level environmental variables.Additionally,multivariate regression analysis identified that the grass growth in the study area was mainly affected by soil temperature and solar radiation,but not by air temperature.High frequency Gcc time series can respond immediately to precipitation events.In the same year,the phenological metrics retrieved from digital cameras and multiple satellites are similar,with spring phenology having a larger relative difference.There are distinct divergences between changing rates in the greenup and senescence stages.Gcc also shows a close relationship with growing degree days(GDD)derived from air temperature.This study evaluated the performance of a digital camera for monitoring vegetation phenological metrics and related climatic factors.This research will enable multiscale modeling of plant phenology and grassland resource management of temperate prairie ecosystems.