Effect of RE~(3+) electronegativities on luminescence property of Ba_5Si_8O_(21):Eu~(2+) persistent phosphor

A series of Ba_5Si_8O_(21):0.02Eu~(2+),0.09RE~(3+) persistent phosphors were synthesized by the solid-state reaction method.The measurement results of photoluminescence(PL),phosphorescence and thermoluminescence(TL)were analysed and discussed.The XRD results showed that samples codoped with different RE~(3+) were Ba_5Si_8O_(21) single pure phase.Under the excitation,all samples exhibited a broad Eu~(2+) characteristic emission,and the La~(3+) co-doped sample emitted the brightest photoluminescence even though its persistent luminescence property was the worst because of the weakest electronegativity.However,Nd~(3+) electronegativity was suitable,thus after activation,the Ba_5Si_8O_(21):Eu~(2+),Nd~(3+) sample had the best persistent luminescence performance with the highest phosphorescence intensity and the persistent luminescence decay time beyond 8 h.The Nd~(3+) co-doped sample also had the largest thermoluminescence integral area which proved effectively it had longer persistent luminescence time.The luminescence mechanism was also proposed to study the photoluminescence and persistent luminescence process.These results showed that RE~(3+) electronegativities were distinctly important for persistent phosphors and choosing suitable electronegativity codopant was conducive to enhancing the phosphorescent performance.     

CsBaB_3O_6:Eu~(3+) red-emitting phosphors for white LED and FED:Crystal structure,electronic structure and luminescent properties

Recently,borate compounds have received much attention in the field of rare earth doped phosphors due to their excellent luminescent performance.In this work,to explore the potential in LED and FED applications,the CsBaB_3 O_6:Eu~(3+) phosphor was investigated in detail by using Rietveld refinement,DFT calculations,photoluminescent and cathodoluminescent spectra.As a result,CsBaB_3 O_6 has a planar stacked three-dimensional layered structure.Under the excitation of 395 nm n-UV light and electron beam,CsBaB_3 O_6:Eu~(3+) phosphor exhibits a typical red emission of Eu~(3+).A good thermal stability and good resistance to saturation and degradation were observed in the CsBaB_3 O_6:Eu~(3+) phosphor.The related photoluminescent and cathodoluminescent mechanisms were studied.The results indicate that CsBaB_3 O_6:Eu~(3+) phosphor has potential in multifunctional applications.     

溶胶-凝胶法制备的BaMgAl10O17:Eu2+荧光性能研究

研究了柠檬酸为络合剂的溶胶-凝胶法制备的BaMgAl10O17Eu2+蓝色荧光粉的荧光性能,考察了Eu 2+掺杂量和晶化温度等因素对荧光粉的紫外和真空紫外波段激发的荧光性能的影响,并通过X射线衍射分析,探讨了Eu2+掺杂量引起的晶胞参数和荧光粉发射波长的变化.结果表明BaMgAl10O17Eu2+随着Eu2+掺杂量的增加,除荧光强度发生变化外,发射光谱的波长发生红移;真空紫外波段激发,Eu2+的最佳添加量为0.1,紫外波段激发下为0.12,发射峰波长均为450 nm;晶化时间2小时,温度在1300℃以上更好.     

Preparation and luminescence properties of rare-earth doped fiber with spectral blue-shift: SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors/triarylsulfonium hexafluoroantimonate based on polypropylene substrate

The rare-earth doped fiber with spectral blue-shift based on long afterglow luminescent materials SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors and an organic cationic photoinitiators-triarylsulfonium hexafluoroantimonate(TSHF) in the presence of polypropylene substrate(PP) was prepared by melt-spinning process. Scanning electron microscopy(SEM), infrared spectroscopy(IR), afterglow properties and luminescence properties were tested. The results of SEM and FTIR spectra showed that the fiber consisted of irregular particles and had independent structural constitution of SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors, TSHF and polypropylene. Furthermore, it was observed that there existed the highest afterglow initial intensity for the fiber with the TSHF concentration of 5 wt.%. More interestingly, the emission peak shifted to blue area gradually as the TSHF doping increased. The rare-earth doped fiber was distributed on blue light area in the CIE 1931 chromaticity diagram, which showed more obvious blue-shift phenomenon than the yellow-green light of SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors.     

Photoluminescence properties and thermal stability of Eu~(3+)-activated La_7Ta_3W_4O_(30) red-emitting phosphors for near-UV-excited w-LEDs

Novel trivalent europium(Eu~(3+))-activated La_7 Ta_3 W_4 O_(30):xEu~(3+)(x=0.5 mol%-40 mol%) red-emitting phosphors were synthesized by means of a high-temperature solid-state reaction.The structure,morphology,photoluminescence,thermal-stability properties,lifetime,and color-rendering of the prepared phosphors were investigated in detail.The La_7 Ta_3 W_4 O_(30):Eu~(3+) phosphors show five emission peaks under near-ultraviolet(n-UV) at 397 nm,and these peaks are ascribed to the transitions of ~5 D_0-~7 F_j(j=0,1,2,3 and 4) by Eu~(3+) ions.The optimal doping concentration of Eu~(3+) is 20 mol%,and the critical distance of the energy transfer between the Eu3+ions was calculated to be 1.768 nm.The quenching temperature(T_(0.5)) of La_7 Ta_3 W_4 O_(30):20 mol%Eu~(3+) is about 440 K.The quantum yield(QY) was measured to be 85.85%.The fabricated white-light-emitting diodes(w-LEDs) possess high color-rendering index(R_a) of 90,and high correlated color temperature(CCT) of 5810 K,respectively.The Commission Internationale de L'Eclairage(CIE) coordinates are(0.311,0.322).Therefore,the prepared phosphor has a promising application for w-LEDs.     

Tunable luminescence and energy transfer in Y_2BaAl_4SiO_(12):Tb~(3+),Eu~(3+)phosphors for solid-state lighting

Single-phase Y₂BaAl₄SiO₁₂:Tb³⁺,Eu³⁺phosphors with adjustable luminescence were successfully prepared by high-temperature solid-state reaction method.The structural,luminescent properties and ene rgy transfer(ET) process of Y₂BaAl₄SiO₁₂:Tb^(³⁺),Eu³⁺phosphors were syste matically analyzed with the help of X-ray diffraction(XRD),scanning electron microscopy(SEM),excitation spectra,emission spectra and photoluminescence decay curves.Tunable luminescence ranging from green through yellow and definitively to red can be achieved by elevating amounts of Eu³⁺ions in Tb³⁺,Eu³⁺co-doped samples.Besides,the ET mechanism and efficiency were also analyzed and the maximum ET efficiency is 67%.All the results show that Y₂BaAl₄SiO₁₂:Tb³⁺,Eu³⁺phosphors can be used in solid-state lighting.     

Luminescence and energy transfer of color-tunable Lu_2MgAl_4SiO_(12):Eu~(2+),Ce~(3+),Mn~(2+) phosphors

Energy transfer among the co-doped activators is an efficient route to achieve color-tunable emission in inorganic phosphors.Herein,photoluminescence tuning from blue to cyan has been achieved in the Lu_2MgAl_4 SiO_(12);Eu~(2+),Ce~(3+)phosphors by varying the Ce~(3+) concentration with a fixed Eu~(2+)content.With the further introduction of a Mn~(2+)-Si4+couple into the host lattice,the emission color can be tuned to red through the energy transfer of Eu~(2+)and Mn~(2+).The luminescence properties and the energy transfer mechanism were studied in detail.The energy transfer from Eu~(2+)to Ce~(3+)is certified as a dipolequadrupole interaction with the energy transfer efficiency of 41.4% and Eu~(2+)to Mn~(2+)belongs to a dipole-dipole interaction with the energy transfer efficiency of 94.3%.The results imply that this singlephased Lu_2MgAl4 SiO_(12):Eu~(2+),Ce~(3+),Mn~(2+)phosphor has a potential prospect for application in near-UV chip pumped white light emitting diodes.     

Optical performance study of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+) ternary luminous fiber

In this study, down-conversion fluorescent powder of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+), which were the common three primary colors materials with long afterglow, were synthesized by high temperature solid state method. The blends of rare earth(RE) luminescent materials have been of interest to reinvest the luminescent characteristics of polyethylene terephtahalate(PET) luminous fiber. The scanning electron microscopy(SEM) and an inversion fluorescence microscope were used to characterize the surface morphology and the dispersion of inclusion. Through analysis of microcosmic morphology, three typical dispersions of luminescent particles were summarized. The X-ray diffraction indicated that the phase structure of fiber samples and crystal structure of luminescence materials kept complete after prilling and spinning. From the fluorescence spectra and CIE 1931 coordinates, it could be found that different combinations of luminous fibers were desired to obtain divers colors emission luminous fiber. And the fiber samples were a light sensation which could induct different excitation wavelengths and convert it down to different colors. The afterglow decay curve and its differential curve were summarized indicating the three decay stages. The decay curve and decay rate curve showed that the contents of Sr_2ZnSi_2O_7:Eu~(2+),Dy~(3+), SrAl_2O_4:Eu~(2+),Dy~(3+) and Y_2O_2S:Eu~(3+),Mg~(2+),Ti~(4+) had obvious influence on the afterglow of fiber samples.     

Luminescent and thermometric properties of dual emitting Eu~(2+)/Sm~(3+) co-doped Sr_4La(PO_4)_3O phosphor based on energy transfer

Eu²⁺/Sm³⁺co-doped dual-emitting Sr₄La(PO₄)₃O phosphors were synthesized through a convenient high temperature solid state reaction in reductive atmosphere.The structure,luminescence,energy transfer and temperature-dependent luminescence properties of Eu²⁺/Sm³⁺co-doped Sr₄La(PO₄)₃O phosphors were researched and analyzed in detail.The blue emission of Eu²⁺and the red emission of Sm³⁺can work together as FIR signals.Based on the different response characteristics of these two ion emissions to temperature,Sr₄La(PO₄)₃O:Eu²⁺/Sm^(³⁺)phosphor achieves the relative sensitivity of0.48384%/K and a wide range of temperature measurements from room temperature to 573 K.The results reveal that the Sr₄La(PO₄)₃O:Eu²⁺/Sm³⁺phosphor has application prospect in the field of high temperature optical thermometry.The energy transfer mechanism is proved to be the dipole-dipole interaction between Eu²⁺and Sm³⁺ions.     

Significant enhancement of blue photoluminescence intensity of Dy~(3+) modified Sr_6Ca_4(PO_4)_6F_2:Eu~(2+) phosphors

Blue-emitting phosphors Sr_6 Ca_4(PO_4)_6 F_2:Eu~(2+)(SCPF:Eu~(2+)),Sr_6 Ca_4(PO_4)_6 F_2:Eu~(2+),Dy~(3+)(SCPF:Eu~(2+),Dy~(3+))and Sr_6 Ca_4(PO_4)_6 F_2:Eu~(2+),Dy~(3+),Si~(4+)(SCPF:Eu~(2+),Dy~(3+),Si~(4+)) with apatite structure were successfully synthesized by traditional solid-state reaction under reducing atmosphere.Eu~(2+),Dy~(3+) and Si4+ions occupy the corresponding sites of Sr~(2+),Ca~(2+) and P~(5+).Strong broad blue photo luminescence band is exhibited in SCPF:Eu~(2+),Dy~(3+) phosphor ranging from 400 to 550 nm centered at 455 nm and Dy~(3+) ions are vital in creating traps.Emission intensity of Eu~(2+),Dy~(3+) co-doped SCPF:0.02 Eu~(2+),0.02 Dy~(3+) is about 1.8 times that of SCPF:0.02 Eu~(2+) and electron trap centers serve as energy transporting media.To further elucidate the formation and effect of the specific defect on the luminescence of SCPF:0.02 Eu~(2+),0.02 Dy~(3+) phosphor,the thermoluminescence properties,decay curves and thermal stability studies were performed while the Si~(4+)-P~(5+) charge compensated pho sphor SCPF:0.02 Eu~(2+),0.02 Dy~(3+),0.02 Si~(4+) was prepared as a contrast.All the results of present work indicate that Dy~(3+) co-doping can obviously enhance photoluminescence intensity of SCPF:0.02 Eu~(2+) by the electron traps generated by non-equivalence replacement of Dy~(3+)-Ca~(2+).     

Luminescence properties of Eu~(3+):NaGd(WO_4_)2 nanoparticles and nanorods

The NaGd(WO_4)_2:Eu~(3+) phosphors were prepared by the microemulsion mediated hydrothermal method. The morphology and size of the samples could be dependent on the p H in the initial solution. These phosphors obtained had a strong absorption at 395 nm matching with the popular emission of near-UV LED chips, and could emit intense red light at 616 nm. The small ellipsoid-like particles or short rods were provided with large parameters of oscillator strength ?_2 and asymmetry ratio. Compared to the ellipsoid-like phosphors, the rod-like phosphors took on stronger emission, longer lifetime and larger quantum efficiency. This work demonstrated that the one-dimension Na Gd(WO_4)_2:Eu~(3+) phosphors might be a more favorable device than zero-dimension ones for photoluminescence.     

Synthesis and characterization of CaAl_xO_y:Eu²⁺ phosphors prepared using solution-combustion method

Europium-doped calcium aluminate(CaAlxOy:Eu2+) phosphors were obtained at low temperatures(500 oC) by the solution-combustion of corresponding metal nitrate-urea solution mixtures.The particle size and morphology and the structural and luminescent properties of the as-synthesized phosphors were examined by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),Auger spectroscopy,transmission electron spectroscopy(TEM) and photoluminescence(PL).It was found that the Ca:Al molar ratios showed greatly influence not only on the particle size and morphology,but also on their PL spectra and structure.With the Ca:Al molar ratios increasing from 6:100 to 26:100,the structure of as-synthesized phosphor changed from CaAl12O19 to monoclinic CaAl2O4 and the dominant emitting light from red to blue,implying that the oxidation state of doped europium ions changed from trivalent to divalent due to the structure variation of host lattice.A blue phosphor with almost pure phase can be easily prepared by solution combustion method with suitable Ca:Al molar ratio.     

Ultraviolet to near-infrared energy transfer in NaYF_4:Nd~(3+),Yb~(3+) crystals

To convert ultraviolet(UV) light into near-infrared(NIR) light in phosphors is demanded for the development of solar cells.A series of NaYF_4:Nd~(3+),Yb~(3+) white powder samples were prepared via the hydrothermal method.The crystal structure and photoluminescence properties of the samples were carefully studied using X-ray diffractometry(XRD) and photoluminescence spectra.The excitation and emission spectra of NaYF_4:Nd~(3+),Yb~(3+) samples and the luminescence decay curves of Nd~(3+) and Yb~(3+) revealed an efficient energy transfer process from Nd~(3+) to Yb~(3+).This process resulted in the Yb~(3+) NIR fluorescent emission at 980 nm.Moreover,the lifetime of the Nd~(3+4)F_(3/2) level decreased with the increase of Yb~(3+) doping concentration.The build-up time of the decay curves of the Yb~(3+2)F_(5/2) level further verified the energy transfer process.Meanwhile,energy transfer efficiency based on different Yb~(3+) doping concentrations was achieved.     

Origin of the red luminescence in Sr_3Al_2O_6:Eu phosphor ——From the synergetic effects of Eu~(2+) and Eu~(3+)

In order to uncover the real origin of red luminescence from Sr_3Al_2O_6:Eu and the physical mechanisms that were involved in the dynamical process of luminescence, variant amount of Eu and Dy activated Sr_3Al_2O_6 phosphors were synthesized with the solid-state reaction and the combustion-assisted solid-state reaction, respectively, using the fine graphite powder or the mixed H_~(2+)N_2gases as a reducing agent. The phase was examined with XRD analysis and the photoluminescence properties were characterized by a fluorescence spectrometer. Although the phosphors possessed the same Sr_3Al_2O_6 phase, different emission colors(red or green) were obtained, relying on synthesis conditions. The simultaneous existence of Eu~(2+) and Eu~(3+) was not only observed in the emission and excitation spectra, but also identified with the near edge X-ray absorption fine structure spectroscopy(NEXAFS).The mixed valence(higher than +2 and less than +3) of Eu may be related with the six different sites of Sr, whose effective valence ranged from +1.5058 to +2.2698, in the crystal lattice of Sr_3Al_2O_6 that could accommodate Eu. Moreover, the reduction of Eu~(3+) to forming Eu~(2+) depended on the amount of Eu~(3+) or Dy~(3+) doped, due to the different energy barrier in each site of Sr that Eu had to overcome. The residual Eu~(3+), similar to the doped Dy~(3+), played an important role in supplying the hole for Eu~(~(2+)) to form a bound trap(Eu~(2+))* after excitation. During electron returning to the 4f~7 ground state of Eu~(2+), the red luminescence was radiated. Therefore, the synergetic effects of Eu~(2+) and Eu~(3+)(Dy~(3+)) produce red luminescence.     

Broadband near-infrared luminescence and energy transfer of Cr~(3+),Ce~(3+) co-doped Ca_2LuHf_2Al_3O_(12) phosphors

Broadband near-infrared phosphors are highly desirable for food testing.Targeted Ca₂LuHf₂Al₃O₁₂:Cr³⁺(CLHA:Cr³⁺) and Ca₂LuHf₂Al₃O₁₂:Ce³⁺,Cr³⁺(CLHA:Ce³⁺,Cr^(³⁺)) phosphors were synthesized by the conventional high-temperature solid state reaction.The CLHA:Cr³⁺phosphor,with a good thermal stability,shows a red shift owing to radiation reabsorption and non-radiative transition with increasing Cr³⁺content.For co-doped sample,the emission intensity of Cr³⁺can be enhanced by three times due to the energy transfer from Ce³⁺to Cr³⁺,which can be evidenced by a significant overlap between the PLE of Cr³⁺single-doped phosphor and the PL of Ce³⁺single-doped phosphor.In addition,the mechanism of energy transfer is identified as a quadrupole-quadrupole interaction according to decay Lifetime and Dexter’s energy transfer formula.The broadband NIR emission peaked at 775 nm of CLHA:Cr³⁺,Ce³⁺phosphor shows a bright prospect in nondestructive quality-control analysis systems for food.     

Highly sensitive up-conversion phosphor for optical thermometry:CaLaAl_3O_7:Er~(3+)/Yb~(3+)

Herein, we reported Er~(3+)/Yb~(3+) co-doped CaLaAl_3O_7 up-conversion phosphors synthesized via solid state reaction, which was further explored as a new optical thermometry. The luminescent properties of Er~(3+) or Er~(3+)/Yb~(3+) doped CaLaAl_3O_7 phosphor was studied in detail. The two-photon process for the green emissions of Er~(3+) were confirmed by the power-dependent luminescence. The up-conversion optical temperature sensing performances of the Er~(3+)/Yb~(3+)-codoped CaLaAl_3O_7 phosphor were investigated based on the FIR technique. The maximum sensitivity of this phosphor can reach about 0.00345 K~(-1) at 453 K, which reveals this phosphor can be a promising candidate for optical thermometry devices.     

Spectroscopic properties and energy transfer of Nd3+/Ho3+-doped Ga2O3-GeO2 glass by codoping Yb3+ ion

This study presented the luminescence properties of Nd³⁺/Yb³⁺/Ho³⁺ dopant ions inside a host based on Ga₂O₃-GeO₂-Li₂O（GGL） glass. The measured differential scanning calorimetry result showed that GGL glass exhibited excellent stability against devitrification with ?T=135 oC. Obvious 543 and 657 nm emissions were observed in Nd³⁺/Ho³⁺-codoped sample. The incorporation of Yb³⁺ into Nd³⁺/Ho³⁺-codoped glass system had resulted in enhanced upconversion emission intensity under the excitation of 808 nm and/or 980 nm laser diode（LD）. The possible mechanisms and related discussions on this phenomenon were presented. It was noted that the presence of Yb³⁺ yielded an enhancement about 7 and 11 times in the 543 and 657 nm emission intensities respectively under 808 nm excitation due to the energy transfer from Nd³⁺ to Ho³⁺ via Yb³⁺ ion. Here Yb³⁺ played a major role as a bridging ion. While enhanced 543 and 657 nm emission intensities under the excitation of 980 nm LD originated from the sensitization effect of Yb³⁺. Our results showed that Nd³⁺/Ho³⁺/Yb³⁺ triply doped GGL glass might be a promising candidate for the development of visible-laser materials.     

Effect of red emitting fluorescent pigment on fluorescent color of SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors

Green-blue fluorescence emitting SrAl_2O_4:Eu~(2+),Dy~(3+) phosphors(SAOED) were coated by SiO_2 and a coumarin type red-emitting fluorescent pigment(FP).The effects of the FP on the morphology,crystal structure,photoluminescence properties and fluorescent color of the SAOED phosphors were systematically investigated by scanning electron microscopy(SEM),FT-IR,X-ray diffraction(XRD),photoluminescence spectra and CIE-1931 chromaticity coordinates characterization.Even though the surface of the SAOED phosphors became rough after being coated with SiO_2 and FP,crystal lattice of SrAl_2O_4 did not have any obvious lattice distortions.The photoluminescence spectra indicated that the SAOED phosphors could be used as the excitation light source to excite the FP to emit red fluorescence.The emission spectrum of the FP-coated SAOED consisted of a broad band with two emission peaks at 520 and 610 nm,and its fluorescence emission color was a mixed color of the SAOED phosphors and FP.The fluorescence color of the SAOED/SiO_2/FP composites tended to transfer to red area with the increase of the FP content varying from 0.1%to 0.9%.     

Red long lasting phosphorescence of Eu~(3+) doped BiOCl semiconducting polycrystals

The exploration of novel long lasting red phosphors is still of importance due to expected commercial applications and scientific interests. In this work, we reported the red long lasting phosphorescence(LLP) from Eu~(3+) doped BiOCl semiconductor polycrystals. The LLP property of the red phosphor is relatively weak due to less trap density, but the excitation band of LLP stems from the energy gap transition of semiconductor, offering experimental evidence for energy transfer between BiOCl semiconductor and Eu~(3+) ions. Although the afterglow duration of Eu~(3+) doped BiOCl was short temporarily, this work may open a novel kind of red LLP phosphors.     

Sensitizing effect of Nd~(3+) on Tb~(3+) activated ZrP_2O_7 long persistent phosphor materials

The long persistent phosphors of Zr_(0.97)P_2 O_7:0.018 Tb~(3+),0.012 Nd3+with Nd~(3+)as sensitized ions and Tb~(3+)as emission centers were synthesized using high temperature solid state reaction.The crystal structure and defects,excitation and emission spectra,decay curves and thermoluminescence(TL) curves of the phosphors were investigated.The synthesized Zr_(0.97)P_2 O_7:0.018 Tb3+,0.012 Nd3+is essentially in line with the standard card PDF#49-1079.The emission band with main peak at 548 nm exhibits the characteristic transitions of ~5 D_3-~7 F_j(j=5,4) and ~5 D3-~7 F_j(j=6,5,4,3) of Tb~(3+).The analysis of excitation and emission spectra shows that there exists the overlap between the emission peaks of Nd~(3+)at 466 and 485 nm and the excitation of Tb3+at 443 and 485 nm,and the energy transfer from Nd3+to Tb3+plays an important role in the improvement of luminescence properties.The decay curves shows that Zr_(0.97)P_2 O_7:0.018 Tb3+,0.012 Nd3+has longer afterglow time than ZrP_2 O_7 and Zr_(0.982)P_2 O_7:0.018 Tb3+.Additionally,the TL curves indicate that the trap depth at 0.72 eV in Zr_(0.97)P_2 O_7:0.018 Tb~(3+),0.012 Nd3+is to the benefit of the afterglow time.The possible luminescence mechanism of ZrP_2 O_7:Tb~(3+),Nd3+is proposed on the basis of the XPS spectra,EPR spectra,excitation and emission spectra,decay curves,TL curves and the analysis of defect equations.