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 °C 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.     

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+.     

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.     

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.     

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.     

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.     

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+.     

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.     

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.     

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.     

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.     

Effects of Sr²⁺ on structure and luminescent properties of BaAl₁₂O₁₉:Eu phosphors

Ba0.9-ySryAl12O19:Eu0.1 phosphors were prepared by sol-gel technique,the crystalline structures of samples characterized by XRD,and the luminescence properties were investigated.The influence of crystallographic positions on the luminescent properties of Sr2+-doped BaAl12O19:Eu was investigated in detail.The results indicated that the crystal lattice of BaAl12O19:Eu was not influenced by the Sr2+ and doping Sr2+ in BaAl12O19:Eu enhanced the luminescent properties of the phosphors at the proper concentration of Sr2+.With the increasing of concentration of Sr2+ doped in BaAl12O19:Eu,the relative luminescent intensity of Ba0.9-ySryAl12O19:Eu0.1 strengthened and blue-shifted.     

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.     

Up-conversion luminescence of Tm3+/Yb3+ co-doped oxy-fluoride glasses

The oxy-fluorosilicate glasses co-doped with Yb3+/Tm3+ were prepared.The absorption spectra were recorded.The Tm3+ ion showed two absorption bands,with one at 774 nm due to 1G4→3H6 transition and the other at 667 nm due to 1G4→3F4 transition.The energy transfer between Tm3+ ion and Yb3+ ion and the up-conversion fluorescence of Tm3+ ion were investigated using 980 nm LD excitation.The results showed that the blue and red emissions were three-photon absorption processes corresponding with 1G4→3H6 and 1G4→3F4...     

Effects of aluminum co-doping on photoluminescence properties of Ce³⁺-doped SiO₂ glasses

SiO2 glasses co-doped with Al3+ ions were prepared by a sol-gel method by holding 0.5% of Ce3+ ions constant and varying the Al3+ ions concentrations.Thermal stability,the structural,chemical and the optical properties of the samples were studied by using differential scanning calorimetric(DSC),thermo gravimetric analysis(TGA),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),UV-vis spectroscopy and photoluminescence spectroscopy(PL).The DSC and TGA of samples depicted that the presence of dopant and co-dopant decreased the endothermic peak temperature and the yield respectively.SEM images showed that the particles were in the nano-range and spherical in shape.The XRD showed that all the samples were amorphous.The UV absorption measurements indicated that the presence of Al3+ ions significantly reduced the SiO2 absorption band,increased the absorbance intensity of SiO2 and decreased the transmittance as compared to the presence of the Ce3+ ions alone.The photoluminescence results displayed an optimum increase in luminescence intensity when the ratio of Al:Ce was 10:1 and further increase in aluminum content quenched the luminous intensity.     

Tm3+-doped tellurite glass with Yb3+ energy sensitized for broadband amplifier at 1400-1700 nm bands

A kind of novel experiment was disclosed as it possessed two bands of fluorescence emission at 1.4 and 1.6 μm, which were per-fectly complimentary to the current C band of optic communication. The fluorescence was based on energy transfer and up-conversion proc-esses between Tm3+ and Yb3+ under direct pumping of 975 nm LD. The spectra and lifetimes of Tm3+ fluorescence in the tellurite glass were described. The corresponding fluorescence characteristics and energy migration process were analyzed by the method of lifetime and inten-sity comparison. The mechanism of the up-conversion based IR fluorescence was presented upon analyzing the multi-photon pumping proc-ess. The potential advantages of Tm3+/Yb3+ co-doped tellurite glass as amplifier material were concluded.     

Energy transfer in Tb~（3＋）,Yb~（3＋） codoped Lu_2O_3 near-infrared downconversion nanophosphors

Tb3+ and Yb3+ codoped Lu2O3 nanophosphors were synthesized by the reverse-strike co-precipitation method. The obtained Lu2O3:Tb3+,Yb3+ nanophosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD results showed that all the prepared nanophosphors could be readily indexed to pure cubic phase of Lu2O3 and indicated good crystallinity. The Tb3+→Yb3+ energy transfer mechanisms in the UV-blue region in Lu2O3 nanophosphors were investigated. The experimental results showed that the strong visible emission around 543 nm from Tb3+ (5D4→7F5) and near-infrared (NIR) emission around 973 nm from Yb3+ (2F5/2→2F7/2) of Lu2O3:Tb3+,Yb3+ nanophosphors were observed under ultraviolet light excitation, respectively. Tb3+ could be effectively excited up to its 4f75d1 state and relaxed down to the 5D4 level, from which the energy was transferred cooperatively to two neighboring Yb3+. The Yb3+ concentration dependent luminescent properties and lifetimes of both the visible and NIR emissions were also studied. The lifetime of the visible emission decreased with the increase of Yb3+ concentration, verifying the efficient energy transfer from the Tb3+ to the Yb3+. Cooperative energy transfer (CET) from Tb3+ to Yb3+ was discussed as a possible mechanism for the near-infrared emission. When doped concentrations were 1 mol.% Tb3+ and 2 mol.% Yb3+, the intensity of NIR emission was the strongest.     

Photocatalytic degradation of pesticide residues with RE³⁺-doped nano-TiO₂

The photocatalytic degradation effects of carbofuran solution under concentration of 0.2,0.4,0.8 g/L Re3+-doped nano-TiO2 were studied.The highest degradation rate of 54.89% was obtained after 4 h degradation when the concentration of nano-TiO2 was 0.4 g/L.Then field trials of photocatalytic degradation with suspension nano-TiO2 were conducted.The photocatalytic degradation effect of organic phosphorus and carbamate pesticides in tomato leaves and soil with different concentratio catalyst(0,0.2,0.4,0.6,0.8 g/L) were studied.The results showed that nano-TiO2 could significantly increase photocatalytic degradation rate of pesticide residues in tomato leaves and soil.Pesticide residues degradation rate could be increased by 20%-30% on the tomato leaves and 15%-20% in soil,and the best concentration of photocatalytic degradation was 0.2-0.4 g/L.     

Upconversion luminescence of Yb3+/Ho3+/Er3+/Tm3+ co-doped KGd(WO4)2 powders

Different lanthanide ions (Yb3+/Ho3+/Er3+/Tm3+) codoped KGd(WO4)2 phosphors were prepared by high-temperature solid-state reaction. The upconversion luminescence properties of two-ion and three-ion co-doped KGd(WO4)2 phosphors were investigated in detail. The concentration quenching effect of the two-ion co-doped KGd(WO4)2 phosphors was studied, and the optimum concentration of Ho3+, Er3+ and Tm3+ are 2 mol.%, 2 mol.% and 3 mol.%, respectively. The Yb3+/Ho3+/Tm3+ co-doped KGd(WO4)2 sample is the best white ...     

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.