Luminescent properties of Eu3+-doped BaZrO3 phosphor for UV white light emitting diode

A novel orange phosphor Eu³⁺ doped barium zirconate (BaZrO₃) was synthesized by conventional solid state reaction method and its crystal structure and luminescent properties were investigated in this paper. The X-ray diffraction patterns (XRD) showed that simple BaZrO₃ phase was obtained. Monitoring at 596 nm, the excitation spectrum consisted of a broad band and a series of narrow bands and the stronger excitation peaks located at 275 and 393 nm, respectively. The emission spectrum excited by 393 nm UV light was composed of four narrow bands. The strongest emission was located at 596 nm. The appropriate concentration of Eu³⁺ was 0.025 (molar fraction) for the highest emission intensity at 596 nm. The H₃BO₃ and ammonium were added as flux and the results showed that 2 wt.% NH₄F ions was the optimal flux for BaZrO₃:Eu³⁺.     

Electrospinning synthesis and luminescent properties of Lu₂O₃:Eu³⁺ nanofibers

One-dimensional Lu2O3:Eu3+ nanofibers were prepared by electrospinning followed by high-temperature calcinations.Thermogravimetric and differential thermal analysis,X-ray powder diffraction,Fourier transform infrared spectroscopy,scanning electron microscopy,photoluminescent spectra and decay curves were used to characterize the samples.Results showed that samples began to crystallize at ～500 oC and crystallized completely around 1000 oC.The average diameter of nanofibers(1000 oC annealed) was about 55 nm and the particle size of Lu2O3:Eu3+ increased with increasing annealing temperature.Under ultraviolet excitation,nanofibers exhibited typical red emission of Eu3+ in Lu2O3.The effect of heat-treatment temperature on luminescent properties of nanofibers was also discussed.     

Luminescence properties of BaAl₁₂O₁₉:Tb,Ce and energy transfer between Ce³⁺,Tb³⁺

BaAl12O19:Tb,Ce phosphors were prepared by sol-gel technique,the crystalline structures of samples characterized by XRD,and the luminescence properties and energy transfer between Ce3+ and Tb3+ were investigated.The results indicated that the emission intensity and the excitation wavelength range of Tb3+ increased when Ce3+ was doped.It demonstrated that the Ce3+ added in the BaAl12O19:Tb could deliver energy to Tb3+,and Ce3+ was not luminous by itself.The relative emission intensity of Tb3+ at wavelength of 548 nm was the strongest by Tb3+/Ce3+ ratio of 2:1,when excited at 310 nm,which was the characteristic adsorption wavelength of Ce3+.     

Re-determination of the crystal structure of Ca₂Y₈Si₆O₂₆ and study on the luminescent properties of Ca₂Y₈Si₆O₂₆:Tb³⁺

The crystal structure of silicate oxyapatite Ca2Y8Si6O26 was indexed as hexagonal,space group P63/m,a=0.93515 nm,c=0.67872 nm,α=β=90°,γ=120°,V=0.5138692 nm3.Three strong peaks located at 32.079o,32.595o,and 50.104o with d=2.7903,2.74649,1.8194 was in accordance with,(112),and(213) planes.The optimum concentration of Tb3+ in Ca2Y8Si6O26 to yield highest photoluminescence intensity was 10 mol.% of Y3+.The corresponding excitation spectrum consisted of an intense broad band from 220 to 260 nm.The photoluminescence measurements showed that the green emission originated from 5D4-7F5 was predominant in the measured range with strong doublet lines at 543 and 549 nm.     

Photoluminescence study of SiO₂ coated Eu³⁺:Y₂O₃ core-shells under high pressure

Uniform core-shell Eu3+:Y2O3/SiO2 spheres were synthesized via precipitation and the Stber method.The structural transition of core-shell Eu3+:Y2O3/SiO2 was studied by using high pressure photoluminescence spectra.With pressure increasing,the emission intensities of 5D0→7F0,1,2 transitions of Eu3+ ions decreased and the transition lines showed a red shift.The relative luminescence intensity ratio of 5D0→7F2 to 5D0→7F1 transitions decreased with increasing pressure,indicating lowering asymmetry around Eu3+ ions.During compression,structural transformation for cores in the present core-shell Eu3+:Y2O3/SiO2 sample from cubic to monoclinic took place at 7.5 GPa,and then the monoclinic structure turned into hexagonal above 15.2 GPa.After the pressure was released,the hexagonal structure transformed back to monoclinic and the monoclinic structure was kept stable to ambient pressure.     

Combustion synthesis of Ce~（3＋）, Eu~（3＋） and Dy~（3＋） activated NaCaPO_4 phosphors

The preparation of NaCaPO4 doped with rare earth (RE) ions Ce3+, Eu3+ and Dy3+ by combustion method was described. Under UV excitation (251 nm) of NaCaPO4:Ce3+ showsd emission (367 nm) in UV range. When NaCaPO4:Dy3+ phosphor was excited at 349 nm, the emission spectrum showed intense bands at 482 nm (blue) and 576 nm (yellow). In Eu activated NaCaPO4 phosphor, the emission spectrum showed a dominant peak at 594 nm (orange) while others were at 614 and 621 nm (red) when excited at 393 nm. The prepared phosph...     

Intense blue-emitting Ca₂PO₄Cl:Eu²⁺ phosphor for near-ultraviolet converting white light-emitting diodes

A blue phosphor Ca2PO4Cl:Eu2+(CAP:Eu2+) was synthesized by solid state reaction.The Ca2PO4Cl:Eu2+ exhibited high quantum efficiency and excellent thermal stability.The luminescent intensity of Ca2PO4Cl:Eu2+ was found to be 128% under excitation at 380 nm,149% under 400 nm,and 247% under 420 nm as high as that of BaMgAl10O17:Eu2+.The optimal doping concentration was observed to 11 mol.% of CAP:Eu2+.The energy transfer between Eu2+ ions in CAP were occurred via electric multipolar interaction,and the critical transfer distance was estimated to be 1.26 nm.A mixture of blue-emitting Ca2PO4Cl:Eu2+,green-emitting(Ba,Sr)2SiO4:Eu2+ and red-emitting CaAlSiN3:Eu2+ phosphors were selected in conjunction with 400 nm chip to fabricate white LED devices.The average color-rendering index Ra and correlated color temperature(Tc) of the white LEDs were found to be 93.4 and 4590 K,respectively.The results indicated that it was a promising candidate as a blue-emitting phosphor for the near-UV white light-emitting diodes.     

Luminescent properties of Ca2SiO4:Eu3+ red phosphor for trichromatic white light emitting diodes

The luminescent properties of Eu3 doped Ca2SiO4 red phosphors synthesized by the flux fusion reaction method were investigated. It was found that the excitation spectrum included two regions: the weak excitation band below 325 nm and strong narrow peaks above 325 nm. The main peak of the excitation band was located at 400 nm. The peaks located at 290 nm were assigned to the combination of the charge transfer transition of O-Eu, peaks above 325 nm (325, 385, 400, 470, 511, and 539 nm) were assigned to the f–f transitions of Eu3 . The emission spectrum was dominated by the red peak located at 612 nm due to the electric dipole transition of 5D0–7F2. In addition, the ef- fects of the Eu3 content and charge compensators of Li , Na , K , and Cl– ions on the emission intensity were investigated. The experiment results suggested that the strongest emission was obtained when the concentration of the Eu3 ions was 0.3 mol–1, and Li ions gave the best improvement to enhance the emission intensity. Ca2SiO4:Eu3 , Li was thus suitable for low-cost trichromatic white light emitting diodes (WLED) based on UV InGaN chip.     

Energy transfer from Tb³⁺ to Eu³⁺ in zinc lead borate glass

In order to sensitize the luminescence of Eu3+ ions in heavy metal glass,zinc lead borate glass samples containing various concentrations of Eu3+ and Tb3+ ions were prepared to study the Tb3+ to Eu3+ non-radiative energy transfer phenomena.Energy level structures of Tb3+ and Eu3+ ions were plotted to show the excitation and energy transfer routes.Efficient energy transfer from Tb3+ to Eu3+ was observed and studied qualitatively in terms of doping concentrations.The sensitization turned out to be less effective than expected.Further studies to characterize the oxidation of Tb3+ into tetravalent state and to examine the mechanism of energy transfer are proposed.     

Size dependence of up-conversion luminescence of NaYF₄:Yb³⁺/Tm³⁺

Tm3+/Yb3+ codoped NaYF4 microcrystals were synthesized using a hydrothermal method.The bright upconversion light was observed under 980 nm excitation.The upconversion luminescence was systematically investigated at different Yb3+ concentrations and different reaction temperatures and time.The sample with 60% Yb3+ concentration and reacting at 180 oC for 24 h possessed the highest luminescent efficiency.The higher luminescent efficiency was contributed to a large surface area.The large surface area induced the large vibration mode by absorbed H2O and CO2.The larger vibration mode could enhance the energy transfer efficiency from the excited Yb3+ to Tm3+ by the process of phonon assisted energy transfer.     

Pressure effect on optical properties and structure stability of LaPO₄:Eu³⁺ hollow spheres

Uniform monoclinic monazite structure LaPO4:Eu3+ hollow spheres were s ynthesized via an attractive hydrothermal method owing to the higher yield and s implicity.Photoluminescence and Raman spectra of the sample were investigated u nder high pressure up to 26 GPa using diamond anvil cells.At ambient pressure,the sample exhibited same luminescent properties with that of bulk monazite LaPO 4:Eu3+.With the increase of pressure,the emission intensity of Eu3+ decreased and the half-widths of transition lines increased,while emission peaks showed a red shift toward longer wavelengths due to increase in crystal-field strength.No phase transformation appeared before amorphization for monoclinic LaPO4:Eu3+ hollow spheres,which was confirmed based on the analysis of high pressure Raman spectra.The large surface energy of hollow spheres was proposed to prevent the occurrence of phase transformation.     

Controlled synthesis and tunable luminescence of NaYF₄:Eu³⁺

High quality NaYF4:Eu3+ luminescent materials were successfully synthesized via a facile template technique by hydrothermal method.The samples were characterized by X-ray powder diffraction(XRD),transmission electron microscopy(TEM) and fluorescence spectroscopy(FS).The incorporating of Eu3+ ions into NaYF4 crystal lattice influenced the symmetry types of NaYF4 crystals,resulting in phase transformation of NaYF4 crystals between α and β phase.The pure hexagonal phase of branched NaYF4:Eu3+ was obtained as the Eu3+ concentration reached 15 mol.%.In addition,the luminescence color was tuned by changing the doping concentration of Eu3+ ions.     

Optimization of BaMgAl₁₀O₁₇:Eu²⁺ phosphors by the substitution of Si-N bonds for Al-O bonds

We proposed a simple method to improve the thermal stability of BaMgAl10O17:Eu2+(BAM) phosphors by the substitution of Si-N bonds for Al-O bonds in the host lattice.Both photoluminescence properties and thermal stability under ultraviolet(UV) and vacuum ultraviolet(VUV) excitation could be significantly improved through Si-N incorporation.After thermal degradation at 600 °C for 1 h in air atmosphere,the Si-N doped sample(Ba0.88Eu0.12MgAl9.97Si0.03O16.97N0.03) had the highest emission intensity which was 22% and 40% stronger than that of as-received sample under UV and VUV excitation,respectively.This could be attributed to the stable local structure surrounding the Eu2+ ions and the lower electronegativity of nitrogen.     

Hydrothermal synthesis,structure study and luminescent properties of YbPO₄:Tb³⁺ nanoparticles

YbPO4:Tb3+ were synthesized by mild hydrothermal method.The luminescent properties,morphologies and structure of the obtained powders were characterized by photoluminescence(PL) spectra,FESEM,X-ray diffractometer(XRD) and FTIR.The results showed that the prepared YbPO4:Tb3+ nanoparticles were pure tetragonal phase and the average grain size varied with increasing of Tb3+ concentration.Hydrothermal temperature was revealed to be the key factor to enhance the emission intensity of YbPO4:Tb3+ phosphors.The spherical nanoparticles could be effectively excited by near UV(369 nm) light and exhibited green performance at 543 nm(5D4→7F5),489 nm(5D4→7F6) and 586 nm(5D4→7F4).The CIE chromaticity was calculated to be x=0.298,y=0.560.The YbPO4:Tb3+ nanoparticles exhibited potential to act as UV absorber for solar cells to enhance the conversion efficiency.     

Facile synthesis of visible light excited La_1-xGd_xF₃:Eu³⁺ micro-meter sphere using polyvinylpyrrolidone as a template

Lanthanide fluorides exhibited unique luminescent properties in terms of their low phonon energy can restrict the luminescence quenching and extend luminescent lifetimes.Here,a room-temperature co-precipitation method was used to synthesize europium(III) activated La1-xGdxF3 solid phosphors.X-ray diffraction(XRD) data confirmed the crystalline phases of synthesized sample belongs to orthorhombic system.All the as-derived materials exhibited red luminescence(5D0→7F1) under the excitation at longer wavelengths(394 and 466 nm).The powder with the most intense emission was achieved in terms of 10 mol.% doping concentration(Eu content,La/Gd=1/9) and sample sintered at 700 oC.Scanning electron microscopy(SEM) investigated the morphology and crystalline of the samples,showing that many regular and large balls(5-10 μmol/L) were dispersed within the micro-meter scale composites.We proved that the above crystal growth structures were controllable and predicable based on the surface functionalization by polyvinylpyrrolidone ligand.     

白光LED用LaPO4:Eu3+红色荧光粉的合成与表征

利用水热法制备了性能稳定的红色荧光粉LaPO4:Eu3+,同时研究了不同的Eu3+浓度、煅烧温度对荧光粉发光性能的影响.通过X射线粉末衍射(XRD)和扫描电子显微镜(SEM)来表征荧光粉的晶体结构和颗粒大小及形貌;用激发光谱和发射光谱以及荧光衰减曲线来表征荧光粉的荧光性能.结果表明:未煅烧时前躯体主要是六方晶相LaPO4·0.5H2O,煅烧温度在900℃时,所制备样品为单斜相LaPO4:Eu3+;SEM图像显示5 at.%Eu3+掺杂LaPO4呈椭球形,颗粒长约为500 nm,宽约为300 nm.最大发射波长和激发波长分别为592 nm和393 nm,发射光谱中592 nm和612 nm的发射峰对应的是Eu3+离子的5D0→7F1和5D0→7F2跃迁.其荧光寿命为3.32 ms.     

Synthesis of well oil-dispersible BaYF₅:Yb³⁺/Er³⁺ nanocrystals with green upconversion fluorescence

Nearly monodisperse,regular-shaped and well oil-dispersible tetragonal BaYF5:0.2Yb3+/0.02Er3+ nanocrystals(NCs) were synthesized in water-ethanol-oleic acid-sodium oleate system.The as-obtained NCs exhibited bright upconversion(UC) fluorescence under the 980 nm excitation.Blue(2H9/2-4I15/2),green((2H11/2,4S3/2)-4I15/2) and red(4F9/2-4I15/2) transitions were observed.The results indicated that the relative intensity of green to red increased gradually with increasing power density,which were seldom in the previous work.Therefore,the UC properties and mechanism were studied in detail.     

Luminescence properties of BaB8O13：Eu under UV and VUV excitation

The phosphor BaB8O13:Eu3+ were synthesized by solid-state reaction, and their luminescent properties were studied under 254 and 147 nm excitation. The excitation spectrum showed two broad bands in the range of 100-300 nm: one was the host lattice absorption with the maxima at 160 nm and the other was Ba-O absorption overlapped with the CT band of Eu3+, which indicated that the energy of the host lat-tice absorption could be efficiently transferred to the Eu3+. The overlapped bands were tended to separate when monitored by different wave-length, which indicated that at least two Ba2+ sites were available in BaB8O13. The emissions of Eu3+ (612 nm) and Eu2+ (405 nm) were both observed in the emission spectra of BaB8O13:Eu3+ under the excitation of either 254 or 147 nm. With the doping concentration of Eu3+ in-creasing, the 612 nm emission was enhanced while 405 nm emission was decreased under 254 nm excitation, which was due to the persistent energy transfer from Eu2+ to Eu3+. While under 147 nm excitation, the 612 nm emission was quenched and the 405 nm emission was en-hanced. It was concluded that the preferential excitation of Eu2+ under 147 nm excitation was one of the reasons for this facts.     

Vacuum ultraviolet excited photoluminescence properties of Gd2O2CO3:Eu3+ phosphor

The Gd2O2CO3:Eu3 with type-II structure phosphor was successfully synthesized via flux method at 400℃ and their photoluminescence properties in vacuum ultraviolet (VUV) region were examined. The broad and strong excitation bands in the range of 153-205 nm owing to the CO32- host absorption and charge transfer (CT) of Gd3 -O2- were observed for Gd2O2CO3:Eu3 . Under 172 nm excitation, Gd2O2CO3:Eu3 exhibited strong red emission with good color purity, indicating Eu3 ions located at low symmetry sites and the chromaticity coordination of luminescence for Gd2O2CO3:Eu3 was (x=0.652, y=0.345). The photoluminescence quenching concentration of Eu3 excited by 172 nm for Gd2O2CO3:Eu3 was about 5%. Gd2O2CO3:Eu3 would be a potential VUV-excited red phosphor applied in mercury-free fluorescent lamps.     

Photoluminescence Characteristics of Gd2Mo3O9 ： Eu Phosphor Particles by Solid State Reaction Method

Eu^3＋-doped Gd2Mo3O9 was prepared by solid-state reaction method using Na2CO3 as flux and characterized by powder X-ray diffractometry. According to X-ray diffraction, this material belonged to a tetragonal system with space group I41/α. The effects of flux content and sintering temperature on the luminescent properties were investigated with the emission and excitation spectra. The results showed that flux content and sintering temperature had effects on the luminescent properties, the optimized flux content and the best temperature was 3 % and 800 ℃ respectively. The excitation and emission spectra also showed that this phosphor could be effectively excited by C-T band （280 nm）, ultraviolet light 395 nm and blue light 465 nm. The wavelengths at 395 and 465 nm were nicely fitting in with the widely applied output wavelengths of ultraviolet or blue LED chips. Integrated emission intensity of Gd2Mo3O9 ： Eu was twice higher than that of Y2O2S ： Eu^3 ＋ under 395 nm excitation. The Eu^3＋ doped Gd2Mo309 phosphor may be a better candidate in solid-state lighting applications.