Luminescence characteristics of Eu^(3+) activated borate phosphor for white light emitting diode

In this paper, the Sr3Y2 （BO3）4 ：Eu^3＋ phosphor was synthesized by high temperature solid-state reaction method and the luminescence characteristics were investigated. The emission spectrum exhibits one strong red emission at 613 nm corresponding to the electric dipole 5^Do-7^F2 transition of Eu^3＋ under 365 nm excitation, this is because Eu^3＋ substituted for Y^3＋ occupied the non-centrosymmetric position in the crystal structure of Sr3Y2（BO3）4. The excitation spectrum indicates that the phosphor can be effectively excited by ultraviolet （254 nm, 365 nm and 400 nm） and blue （470 nm） light. The effect of Eu^3＋ concentration on the red emission of Sr3Y2（BO3）4 ：Eu^3＋ was measured, the result shows that the emission intensities increase with increasing Eu^3＋ concentration, then decrease. The Commission Internationale del＇Eclairage chromaticity （x, y） of Sr3Y2（BO3）4 ：Eu^3＋ phosphor is （0.640, 0.355） at 15 mol% Eu^3＋.

A novel yellow phosphor for white light emitting diodes

This paper reports that a novel yellow phosphor, LiSrBO3：Eu2＋, was synthesized by the solid-state reaction. Thc excitation and emission spectra indicate that this phosphor can be effectively excited by ultraviolet （360 and 400 nm） and blue （425 and 460 nm） light, and exhibits a satisfactory yellow performance （565 nm）. The role of concentration of Eu2＋ on the emission intensity in LiSrBO3 is studied, and it is found that the critical concentration is 3 mol%, and the concentration self-quenching mechanism is the dipole-dipole interaction according to the Dexter theory. White light emitting diodes were generated by using an InGaN chip （460 nm or 400 nm） with LiSrBO3：Eu2＋ phosphor, the CIE chromaticity is （x = 0.341, y =0.321） and （x = 0.324, y = 0.318）, respectively. Therefore, LiSrBOa：Eu^2＋ is a promising yellow phosphor for white light emitting diodes.

Fabrication of High Color Rendering Index White Light Emitting Diodes from Gold Nanoclusters

We demonstrated gold nanoclusters as color tunable emissive light converters for the application of white light emitting diodes (WLEDs). A blue LED providing 460 nm to excite gold nanoclusters mixed with UV curable material generates broad bandwidth emission at the visible range. Increasing the amount of gold nanoclusters, the correlated color temperature of WLEDs tuned from cold white to warm white, and also results in the variation of color rendering index (CRI). The highest CRI in the experiment is 92.

Realization of warm white light emitting in single phase Gd(P_(x)V_(1−x))O_(4):y at% Sm^(3+),1 at% Bi^(3+) phosphor

A series of single phase,warm white light emitting phosphors,Gd(P_(x)V_(1−x))O_(4):y at%Sm^(3+),with 1 at%Bi^(3+) doping concentration were synthesized by high temperature solid state method in this work.The experimental results indicate broadband cyan emission of Bi^(3+)and characteristic orange-red emission of Sm^(3+)can be effectively tuned by changing the ratios of PO^(3−)_(4)/VO^(3−)_(4) in Gd(P_(x)V_(1−x))O_(4):1 at%Sm^(3+),1 at%Bi^(3+),and the energy transfer process among VO^(3−)_(4),Sm^(3+),Bi^(3+) also can be adjusted.Based on this,warm white light emitting can be realized by further optimizing the doping concentration of Sm^(3+) in the phosphors.At 423 K,the PL intensity of Gd(P_(0.7)V_(0.3))O_(4):2 at%Sm^(3+),1 at%Bi^(3+) remains~84.3%of the initial value at 293 K,while the measured quantum efficiency is 67.8%.EL spectrum analysis results of the fabricated white light emitting diode(wLED)based on a 310 nm UV-chip and Gd(P_(0.7)V_(0.3))O4:2 at%Sm^(3+),1 at%Bi^(3+)phosphors imply low correlated color temperature(3132 K)and appropriate color-rending index(R_(a)=82.7).These results demonstrate that Gd(P_(0.7)V_(0.3))O4:2 at%Sm^(3+),1 at%Bi^(3+)is a good candidate for manufacturing UV-activated warm white light emitting diodes.

Temperature effects on output characteristics of quantum dot white light emitting diode

In this paper, we proposed quantum dot （QD） based structure for implementation of white light emitting diode （WLED） based on InGaN/GaN. The proposed structure included three layers of InGaN QD with box shapes and GaN barriers. By using of single band effective mass method and considering strain effect, piezoelectric and spontaneous polarizations internal fields, then solving Schr/Sdinger and Poisson equations self consistently, we obtained electron and hole eigen energies and wave functions. By evaluating dipole moment matrix elements for interband transitions, the output intensity was calcu- lated due to the interband transition between two energy levels with highest emission probability. We adjusted QDs dimensions and material compositions so that the output light can be close to the ideal white light in chromaticity diagrams. Finally, effects of temperature variations on output spectrum and chromaticity coordinates were studied. We demonstrated that temperature variations in the range of I00 to 400K decrease output intensity, broaden output spectral profile and cause a red shift in three main colors spectrums. This temperature variation deviates （x, y） are coordinated in the chromaticity diagram, but the output color still remains close to white.

Highly Efficient and Stable Hybrid White Organic Light Emitting Diodes with Controllable Exciton Behavior by a Mixed Bipolar Interlayer

Highly efficient and stable hybrid white organic light-emitting diodes （HWOLEDs） with a mixed bipolar interlayer between fluorescent blue and phosphorescent yellow emitting layers are demonstrated. The bipolar interlayer is a mixture of p-type diphenyl （l0-phenyl-lOH-spiro [acridine-9,9＇-fluoren]-3Lyl） phosphine oxide and n-type 2＇,2- （1,3,5-benzinetriyl）-tris（1-phenyl-l-H-benzimidazole）. The electroluminance and Commission Internationale de l＇Eclairage （CIE1931） coordinates＇ characteristics can be modulated easily by adjusting the ratio of the hole- predominated material to the electron-predominated material in the interlayer. The hybrid WOLED with a p-type：n-type ratio of 1：3 shows a maximum current efficiency and power efficiency of 61.1 ed/A and 55.8 lm/W, respectively, with warm white CIE coordinates of （0.34, 0.43）. The excellent efficiency and adaptive CIE coordi- nates are attributed to the mixed interlayer with improved charge carrier balance, optimized exciton distribution, and enhanced harvesting of singlet and triplet excitons.

High efficient and high color rendering index white organic light-emitting diodes

We have fabricated high-efficient white organic light-emitting diodes （WOLEDs） using two types of electron transport materials with different electron mobility. The effect of the electron mobility on the device performance is discussed. In addition, to generate the desired white emission and high color rendering index, we perform the structure design of OLED, in which the functions of co-host of blue and green dopants on chromatic-stability are investigated. Experimental results find that the maximum color rendering index reaches as high as 91 at the voltage of 8 V.

White emission from Tm^(3+)/Tb^(3+)/Eu^(3+) co-doped fluoride zirconate under ultraviolet excitation

We synthesize Tm3＋/Tb3＋/Eu3＋ triply-doped ZrF4-BaF2-LaF3-A1F3-NaF （ZBLAN） transparent glass by using a melt-quenching method. Under excitation of 365 nm, the white emission with Commission internationale deL＇Eclairage （CIE） coordinates of （0.33, 0.33） is achieved at the Eu3＋ concentration of 1.1 mol%. The mechanisms for white emission and the energy transfer process of Tb3＋→ Eu3＋ are discussed in terms of the photoluminescence, photoluminescence excitation spectra, and the light emission decay curves. The nature for the Tb3＋ → Eu3＋ energy transfer is described with the aid of an energy level diagram.

Hydrothermal preparation and photoluminescent property of LiY(MoO_4)_2:Pr^(3+) red phosphors for white light-emitting diodes

Praseodymium doped lithium yttrium molybdate Li Y1-8x Pr x（Mo O4）2（x=0.005-0.025） phosphors were successfully prepared by the hydrothermal method. The phase, morphology, and luminescent property of the prepared phosphors were investigated by X-ray diffraction and scanning electron microscopy. The results indicated that doping of Pr^3＋ ions did not change the main phase of the phosphors. The samples emitted red luminescence upon excitation at 453 nm and the strongest emission peak corresponding to the characteristic transition of the Pr3＋ ion： 3P0→3F2 was observed at 657 nm. Li Y（Mo O4）2：Pr^3＋ red phosphors could be effectively excited by blue light emitting-diodes to emit red light; thus, acting as potential candidates for compensating the red light deficiency of cerium doped yttrium aluminum garnet yellow phosphor.

Annealing Temperature-Dependent Luminescence Color Coordination in Eu-Doped AlN Thin Films

AlN was used as a host material and doped with Eu grown on Si substrate by pulsed laser deposition (PLD) with low substrate temperature. The X-ray diffraction (XRD) data revealed the orientation and the composition of the thin film. The surface morphology was studied by scanning electron microscope (SEM). While raising the annealing temperatures from 300˚C to 900˚C, the emission was observed from AlN: Eu under excitation of 260 nm excitation. The photoluminescence (PL) was integrated over the visible light wavelength shifted from the blue to the red zone in the CIE 1931 chromaticity coordinates. The luminescence color coordination of AlN: Eu depending on the annealing temperatures guides the further study of Eu-doped nitrides manufacturing on white light emitting diode (LED) and full color LED devices.

Effect of fluxes on structure and luminescence properties of Y_3Al_5O_(12):Ce^(3+) phosphors

Ce3＋-activated yttrium aluminum garnet （YAG） was prepared by the solid-state reaction, in which H3BO3, LiF, NaF, KF and BaF2 were used as the fluxes. The effect of fluxes on optical properties of phosphors was studied in detail, especially the fluxes of alkali fluorides, which could enhance the emission intensity and change the wavelength of emission peaks. Among these YAG：Ce phosphors, the phosphor sintered with H3BO3 and NaF exhibited the strongest emission. The emission peaks of phosphors prepared with fluxes from LiF to KF were shifted to long wavelength. The effect of NaF concentration on the emission intensity of YAG：Ce was also investigated. The value of emission intensity reached the maximum when the concentration of NaF was 0.5%.

Synthesis and Properties of Eu_(3+) Activated Strontium Molybdate Phosphor

In order to prepare fluorescent material for white Light Emitting Diodes （LEDs）, a new Eu^3＋ activated molybdate phosphor SrMoO4 was fabricated with solid-state method. X-ray diffraction （XRD） showed that the doping of trivalent europium ion reduced the lattice parameters. The excitation and emission spectra indicated that this phosphor could be excited effectively by the visible light, and then emitted red light with the peaks located at 616 and 624 nm. The influence of Eu^3＋ concentration on the luminescent properties of Eu^3＋ doped SrMoO4 was investigated and the 25% （mole fraction） was the appropriate molar concentration. The reaction time and temperature had obvious effect on the luminescent properties. The luminescent intensity reached the strongest when it was sintered at 800 ℃ for 3 h.

A novel white emitting phosphor Ca_2PO_4Cl:Dy^(3+): luminescence, concentration quenching and thermal stability

A novel white emitting phosphor Ca2PO4Cl：Dy^3＋ was synthesized by a solid state method. The luminescence, concentration quenching and thermal stability of Ca2PO4Cl：Dy^3＋ were investigated. Ca2PO4Cl：Dy^3＋ showed three emission peaks, which were located at 483, 575 and 660 nm. Though the ratio of yellow to blue emission intensities showed a similar value, the intensities of yellow and blue peaks were influenced by Dy^3＋ concentration, and the concentration quenching effect was observed. The emission intensity of Ca2PO4Cl：Dy^3＋ as a function of temperature was explored and the emission intensity（at 150 °C） of Ca2PO4Cl：Dy^3＋ was 90.0% of the value at 25 °C, and activation energy was 0.18 eV. The results indicated that Ca2PO4Cl：Dy^3＋ might be conducive to development of white LEDs.

Enhancement and recovery of photoluminescence and stability by multifunctional etching ligands treatment for perovskite nanocrystals

Perovskite nanocrystals(PNCs)have recently become promising optoelectronic materials due to their excellent photophysical properties.However,the highly dynamic binding state between ligands and the surface of PNCs has severely restricted their luminescent properties and stabilities.In this work,1,3-bisbenzyl-2-oxoimidazolidine-4,5-dicarboxylic acid(cycle acid,CA)is introduced as both an etchant and a ligand upon post-synthetic surface treatment of PNCs.By removing the imperfect octahedrons[Pb X_(6)]^(4-)and passivating the surface defects synergistically,this treatment improves photoluminescence quantum yields from 76%to 95%and enhances the stability of PNCs against polar solvent,moisture,heat,and illumination.Meanwhile,CA can effectively and instantly recover the luminescence emission for aged PNCs.As a result,the CA-Cs Pb Br_(3)PNCs and CA-Cs Pb IxBr_(3-x)PNCs are applied as color-converting layers on a blue LED chip for warm white light-emitting diodes(WLEDs)with a color coordinate of(0.41,0.40).Importantly,the CA-based WLED device exhibits superior stability in operational conditions.

Fabrication and temperature-dependent photoluminescence spectra of Zn–Cu–In–S quaternary nanocrystals

A series of Zn-Cu-In-S nanocrystals （ZCIS NCs） are prepared and the optical properties of the ZCIS NCs are tuned by adjusting the reaction time. It is interesting to observe that the temperature-dependent photoluminescence （PL） spectra of the ZCIS NCs show a redshift with decreasing intensity at low temperature （50-280 K） and a blueshift at high temperature （318--403 K）. The blueshift can be explained by the thermally active phonon-assisted tunneling from the excited states of the low-energy emission band to the excited states of the high-energy emission band.

Multicolor emission from lanthanide ions doped lead-free Cs_(3)Sb_(2)Cl_(9) perovskite nanocrystals

The toxicity of lead ions has become the severe challenge for the all-inorganic lead halide p erovskite materials,although some works have rep orted the lead-free perovskite nanocrystals(NCs),the photoluminescence quantum yield(PLQY)of these materials is still unsatisfactory.Meanwhile,because the halogen ions can be easily exchanged,the controllable multicolor emission in perovskite NCs is difficult to realize in current reports.In this work,we introduced lanthanide ions into lead-free Cs_(3)Sb_(2)Cl_(9) perovskite NCs.Benefitting from the energy transfer between Cs_(3)Sb_(2)Cl_(9) perovskite NC host and lanthanide ions,the multicolor emission was realized.Based on controlling the doping concentration of Tb^(3+)and Eu^(3+)ions,the white light emission under UV excitation would be turned easily in the Tb^(3+)/Eu^(3+)codoped NCs.In addition,efficient energy transfer from perovskite NCs to Tb^(3+)or Eu^(3+)ions is beneficial to improving the optical properties of lead-free perovskite NCs,resulting in maximum PLQYs of red,green and white light emission of 22.6%,19.7%and 28.5%,respectively.Finally,a white light emitting device(WLED)was fabricated with a power efficiency of 18.5 lm/W,which presents the Commission Internationale de l'Eclairage(CIE)of(0.33,0.35).

Large scale synthesis of full-color emissive carbon dots from a single carbon source by a solvent-free method

Full-color emissive carbon dots(CDs)hold a great promise for various applications,especially in light emitting diodes(LEDs).However,the existing synthetic routes for CDs are carried out in solutions,which suffer from low yields,high pressures,various byproducts,large amounts of waste solvents,and complicated photoluminescence(PL)origins.Therefore,it is necessary to explore large scale synthesis of CDs with high quantum yield(QY)across the entire visible range from a single carbon source by a solvent-free method.In this work,a series of CDs with tunable PL emission from 442 to 621 nm,QY of 23%-56%,and production yield within 34%-72%,are obtained by heating o-phenylenediamine with the catalysis of KCl.Detailed characterizations identify that,the differences between these CDs with respect to the graphitization degree,graphitic nitrogen content,and oxygen-containing functional groups,are responsible for their distinct optical properties,which can be modulated by controlling the deamination and dehydrogenation processes during reactions.Blue,green,yellow,red emissive films,and LEDs are prepared by dispersing the corresponding CDs into polyvinyl alcohol(PVA).All types of white LEDs(WLEDs)with high colorrendering-index(CRI),including warm WLEDs,standard WLEDs,and cool WLEDs,are also fabricated by mixing the red,green,and blue emissive CDs into PVA matrix by the appropriate ratios.

Preparation and luminescence properties of Ce^(3+)/Dy^(3+)-codoped fluorosilicate glass ceramics

The Ce^3＋and Dy3＋ co-doped fluorosilicate glass and glass ceramics containing SrF2 or CeF3 nanocrystals were prepared under reducing atmosphere. The precipitated nano-crystalline phase shifted from cubic SrF2 to hexagonal CeF3 gradually with the heat treatment temperature increasing flom 620 to 680 ℃. The glass and glass ceramics emitted white light, deriving from a combination of the Ce3＋ blue and the Dy3＋ yellow light. The CIE coordinates could be tuned by adjusting the ratio of Ce3＋/Dy3＋ concentration. The luminescence could be enhanced significantly by annealing the samples at the temperatures lower than 640℃.

Role of oxygen vacancy in rare-earth-free LiCa_(3)Mg(VO_(4))_(3) phosphor: Enhancing photoluminescence by heat-treatment in oxygen flow

As a kind of white light emitting diode(w-LED)with many advantages,rare-earth-free vanadate phosphor has attracted more and more attention.The oxygen vacancies and other surface defects in vanadate oxide have obvious effects on its structure and properties.In order to reveal the specific effects,we heat-treat the original LiCa_(3)Mg(VO_(4))_(3)(LCMV)in an oxygen flow with different time to decrease oxygen vacancies,and find that the lattice distortion of[VO_(4)]tetrahedron caused by oxygen vacancy is effectively reduced.Meanwhile,the crystallinity of the treated samples increases,the surface defects decreases,and the fluorescence intensity increases.The variation of photoluminescence quantum yield(PLQY)with oxygen treatment time is as follows:the enhancement effect firstly reaches the strongest(69.34%)within one hour,then begins to decline after two hours,and finally reaches the platform after three hours and remains basically unchanged.The reason for the enhancement of PLQY is the decrease of oxygen vacancy after one-hour treatment,and the reason for the decrease of PLQY after a further increased treatment time is that the absorption of oxygen and water in air caused by excessive surface defects introduced by oxygen treatment.