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.     

Effect of light conversion agent on luminous properties of a new down-converting material SrAl_2O_4:Eu~(2+),Dy~(3+)/light conversion agent

A new luminous material SrAl_2O_4:Eu~(2+),Dy~(3+)/light conversion agent that can emit red light in the darkness after being excited was fabricated by combining light conversion agent on to SrAl_2O_4:Eu~(2+),Dy~(3+) particles through YsiX3.The morphology of the luminous materials was analyzed by scan electron microscopy(SEM).The emission behavior was evaluated by fluorescence spectrophotometric analysis and the results demonstrated that the emission spectra of samples had a redshift compared to SrAl_2O_4:Eu~(2+),Dy~(3+) and the emission intensity rose dramatically at first and then decreased when the ratio of light conversion agent doping was over 1.4 wt.%.And the emission color of SrAl_2O_4:Eu~(2+),Dy~(3+)/light conversion agent was tuned from green(SrAl_2O_4:Eu~(2+),Dy~(3+))to orange-red.Furthermore,the afterglow property was also investigated,and the results indicated that the afterglow brightness reached 6.5 cd/m~2,and as the light conversion agent concentration increased the brightness intensity decreased.     

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%.     

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+).     

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.     

Structural characterization and optical properties of long-lasting CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors synthesized by microwave-assisted chemical co-precipitation

The present paper reported the structural and luminescent properties of Eu~(2+) and Nd~(3+) doped CaAl_2O_4 phosphor. The samples were prepared by microwave-assisted chemical co-precipitation(MA-CCP), a synthesis technique which is suitable for small and uniform particle that could be used directly without grinding. The effects of different microwave temperatures on structure and photoluminescence behavior were studied. Formation of a phosphor and phase purity were confirmed by X-ray diffraction technique(XRD) with variable microwave temperatures. XRD analysis showed that the phosphors prepared by MA-CCP method at the temperature of 750, 900oC, respectively and solid-state reaction(SSR) method at 1300oC consisted of impurities. Commission Internationale de L'Eclairage(CIE) color coordinates of CaAl_2O_4:Eu~(2+),Nd~(3+) were suitable as blue light emitting phosphor. Excitation and emission peaks of the samples prepared by different methods in this study were almost the same. The images of SEM showed that the size of the phosphors prepared by MA-CCP method reached a submicrometer.     

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.     

Luminescent properties of Dy~(3+)/Eu~(3+) doped fluorescent glass for white LED based on oxyfluoride matrix

Rare earth ion-doped fluorescent glass has become a hotspot due to its characteristics.This work shows that the prepared Dy~(3+)and Dy~(3+)/Eu~(3+)doped glasses have white light emission under ultraviolet excitation.There is a higher yellow light/blue light(Y/B) value,indicating an increase in the covalentity of Dy-O,and decrease in the symmetry with the increasing concentration of dopants(Dy~(3+)).The correlated color temperature(CCT) can be effectively reduced by the red light emission of Eu~(3+),and the order of influence of excitation wavelength on CCT is 395 nm 382 nm 365 nm.The delay curve demonstrates the energy transfer from Dy~(3+)to Eu~(3+).The glass has the characteristics of anti-blue light damage and wide tunable color temperature,which illustrates that it has potential application in the field of white LED.     

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.     

A single-phased white-emitting Ca_2Ga_2GeO_7:Dy~(3+) phosphor with different charge compensation ions

A novel white-emitting Ca_2Ga_2GeO_7:Dy~(3+) phosphor was synthesized via a high-temperature solid-state reaction.The crystal phase was analyzed by X-ray diffraction(XRD),and the photoluminescence(PL) properties were studied by luminescence spectra and fluorescence decay curves.Under the excitation of 347 nm,the obtained phosphor exhibited strong emission in the blue region peaked at 478 nm,yellow at 574 nm and a weak red emission band at 665 nm,corresponding to the characteristic transitions of ~4F_(9/2)to ~6H_(15/2),~6H_(13/2) and ~6H_(11/2) of Dy~(3+),respectively.By varying the doping concentration of Dy~(3+),tunable colors from blue-white to yellow-white were obtained in the phosphors.Besides,by codoping charge compensators(Li~+,Na~+,K~+ and Ga~(3+)) in Ca_2Ga_2GeO_7:Dy~(3+),the optimum CE color coordinate and PL intensity were obtained in Ca_2Ga_2GeO_7:Dy~(3+),K~+.Accordingly,the PL mechanism of Ca_2Ga_2GeO_7:Dy~(3+) was discussed briefly.     

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.     

Synthesis and photoluminescent properties of Eu~(3+)/Dy~(3+) doped SrO-Al_2O_3-SiO_2 glass-ceramics

Eu~(3+)/Dy~(3+) single-doped and co-doped 6SrO-3Al_2O_3-91SiO_2 and 12SrO-6Al_2O_3-82SiO_2 glass and glass-ceramics were synthesized successfully by a sol-gel method. The prepared samples were characterized by the X-ray diffraction, high-resolution transmission electron microscopy, photoluminescent spectra and X-ray photoelectron spectroscopy. The effect of annealing temperature, doped ions and matrix component on the structure and the photoluminescent characteristics was systematically studied. The higher temperature was helpful to form nanocrystals and the amount of SrO and Al_2O_3 could better disperse the rare earth ions in matrix at suitable temperature, and both of them could improve the luminescent intensity. Meanwhile, the doped ions could change the luminescent color by single, codoped and energy transfer. The Sr_2SiO_4 nanocrystals were observed in silicates glasses and became larger with the increase of the annealing temperature and the luminous efficiency of rare-earth(RE) ions could be enhanced when the samples changed from glass state to glass-ceramic state. The results indicated that the photoluminescent properties could be changed through controlling the doped ions, annealing temperature and matrix component.     

Hydrothermal synthesis of uniform CdWO_4:Eu~(3+) microrods as single component for UV-based WLEDs

A series of single-composition emission-tunable CdWO_4:Eu~(3+) uniform size nanorods were synthesized by polyvinylpyrrolidone(PVP) assisted hydrothermal process. The products were measured by powder X-ray diffraction(PXRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), photoluminescence, and fluorescent decay test. The results showed that reaction time, temperature, p H values and Eu~(3+) doped concentration played important roles in determining the morphologies and photoluminescent properties. And we also investigated its use in Ga N LED, warm-white-light could be obtained by the combination of the bright blue light originated from the charge transfer transition in the tungstate groups and the near UV light from LED chip with the red emission from 4f-4f transition of Eu~(3+), respectively. By properly tuning the doping concentration of Eu~(3+), chromaticity coordinates(0.30 0.22) could be achieved under the 380 nm excitation and its color rendering index was 80.6. So it has potential application in warm-WLED and replacing the commercial YAG:Ce phosphor which absence of red band emission.     

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.     

Synthesis and spectroscopic studies of Zn_4B_6O_(13) and Eu/Tb single-doped Zn_4B_6O_(13) phosphors

In this study, Zn_4B_6O_(13), Eu-and Tb-doped Zn_4B_6O_(13) phosphors were prepared by conventional solid state reaction method and the samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and photoluminescence spectroscopy(PL). The doped rare-earth ions had little influence on the crystal structure of Zn_4B_6O_(13), but obviously affected the morphology of Zn_4B_6O_(13) particles. The PL results indicated that the 5% Eu-doped sample and 1% Tb-doped sample had the highest intensity in their respective different concentrations doped samples. The CIE chromaticity coordinates indicated that Zn_4B_6O_(13), Zn_4B_6O_(13):Eu and Zn_4B_6O_(13):Tb showed the three basic colors of blue, red and green, respectively. Evidently, the white light could appear only at appropriate intensity of blue, red and green components.     

Luminescence of halophosphate solid-solution Ca5(PO4)3(F0.8Cl0.2):Eu2+,Mn2+ for WLED

Solid-solution based luminescent materials have been widely explored due to their tunable optical properties in recent years. In this work, instead of more common cation-substitution approach, we investigated the luminescence properties of Eu~(2+) and Mn~(2+) co-doped halophosphate solid solution Ca_5(PO_4)_3(F_(0.8)Cl_(0.2)) via anion substitution synthesized by high temperature solid state reaction method.The formation of the solid solution was confirmed by X-ray diffraction(XRD) characterization, which indicates that the introduction of certain proportion of Cl~-will not make significant change on the Ca_5(PO_4)_3F lattice. We also studied the energy transfer from Eu~(2+) to Mn~(2+) in the host so as to obtain white light emission via adjusting the doping concentrations of Eu~(2+) and Mn~(2+). The white light emission was achieved through combination of Eu~(2+) blue emission and Mn~(2+) red-orange emission with appropriate proportions. The results suggest that Ca_5(PO_4)_3(F_(0.8)Cl_(0.2)):0.01Eu~(2+),0.18 Mn~(2+) could be a potential WLED phosphor working under ultraviolet excitation.     

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.