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.     

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.     

Enhancement of structure stability and luminescence intensity of LiYF_4:Ln~(3+) nanocrystals

LiYF_4 nanocrystals with tetragonal structure were adopted as the host materials for the phosphors and scintillators owing to the low phonon energy and high optical transparency. LiYF_4:Ln~(3+)(Ce~(3+),Eu~(3+)) nanocrystals were fabricated by solvothermal method. Under UV excitation, they could emit visible light. In order to improve the luminescence intensity, the method of co-doping LiYF_4 nanocrystals with Sc was adopted. Sc~(3+) ions could reduce the lattice expansion caused by the doping of Ce~(3+) or Eu~(3+) whose ionic radius was larger than Y~(3+). Crystal structure of Li(Y,Sc)F_4:Ln~(3+) kept much more stable and the luminescence intensity could be significantly enhanced when the concentration of Sc was a moderate value. Thermoluminescence was employed to analyze the electron traps in Li(Y,Sc)F_4:Ce~(3+). Results suggested that the suppression of the generation of electron traps with the co-doping of Sc contributed to the enhancement of luminescence intensity of LiYF_4:Ce~(3+).     

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.     

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.     

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.     

Photostimulated Luminescence and F-centers of Sr_3Ca_2(PO_4)_3X:Eu~(2+)(X=F,Cl,Br)

This paper reports the F-centers and photostimulated luminescence of Eu~(2+)-activated Sr_3Ca_2(PO_4)_3Xcrystals.The influence of various halide ions on the F-centers and their energy level is discussed.The mechanismfor the photostimulated luminescence and valence change of Eu ion in that process have been investigated.     

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.     

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.     

Tunable luminescence,energy transfer and excellent thermal stability of SrMg_2(PO_4)_2:Ce~(3+),Tb~(3+) phosphors for LEDs

A series of novel SrMg_2(PO_4)_2:Ce~(3+),Tb~(3+)(SMP:Ce~(3+),Tb~(3+)) phosphors with tunable emission spectra were produced via high temperature solid phase method.XRD,fluorescence spectrum and fluorescence lifetime for SMP:Ce~(3+),Tb~(3+)were studied in detail.Under the excitation at 308 nm,SMP:Ce~(3+),Tb~(3+) samples can emit high efficiency tunable blue-green light by controlling the proportion of dopant concentration.Through the spectral overlap and the regular change of fluorescence lifetime,it is proved that there is a significant energy transfer between Ce~(3+) and Tb~(3+) in SMP matrix and the energy transfer mechanism is determined to be an electric dipole-dipole interaction with energy transmission efficiency of 55%.In additional,Commission International de L'Eclairage(CIE) color coordinates and thermal stability were studied.All above findings suggest that SMP:Ce~(3+),Tb~(3+)can be regarded as the potential bluish green phosphor for LED applications.     

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.     

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.     

Na_2WO_4:Eu~(3+),Tb~(3+)光致发光材料的发光性质和能量传递

利用溶胶-凝胶法,将激活离子Eu~(3+)和Tb~(3+)以单一或混合的形式掺入体系得到了光致发光材料.分别研究了材料中激活离子Eu~(3+)和Tb~(3+)的含量及其离子之间的能量传递关系.主要利用材料的三维荧光光谱,激发光谱和发射光谱对其的发光性质进行了分析;结果发现,材料中有两个发光中心,分别为Eu~(3+)和Tb~(3+),在不同的波长光的激发下得到的材料的红绿色发光强度不同,而且Eu~(3+)和Tb~(3+)的掺杂浓度比对发光色度影响很大.所以可以根据选择最适合的Eu~(3+)和Tb~(3+)的浓度比来控制材料的发光色,也可以通过不同的激发波长对材料的色度进行微调.     

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.     

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.     

Emission Spectra and Crystallographic Sites of Eu~(2+) in Ca_8Zn(SiO_4)_4Cl_2

The fluorescent characteristic and emission spectra of Eu~(2+) in the cubic structureCa_8Zn(SiO_4)_4Cl_2 with three kinds of cation sites is reported.The influence of temperature,Eu~(2+) concentra-tion and excitation conditions on fluorescent properties of Eu~(2+) are studied at 77 and 298 K.Thecoordination number of Eu~(2+) at different sites is obtained.The green and red emission bands arise fromEu_(2+) ions locating on eight- and six- coordinated inequivalent sites respectively.     

Synthesis and photoluminescent characteristics of Eu~(3+)-doped MMoO_4(M=Sr,Ba) nanophosphors by a hydrothermal method

The europium ions doped MMoO_4(M=Sr,Ba)nanophosphors were successfully synthesized via a facile hydrothermal method using isopropanol.The relationship between phosphor crystalline phase,morphology,photoluminescent properties and hexadecyl trimethyl ammonium bromide(CTAB)concentration,pH value in precursor solution was investigated.The results indicated that the morphology and photoluminescent properties were strongly influenced by CTAB concentration and pH value in precursor solution.In SrMoO_4:Eu~(3+) hosts,the phosphor surface tended to become smoother as the concentration of CTAB was increased;while particles tended to agglomerate as increasing pH value.The relative intensity ratio of charge transfer band to Eu~(3+) characteristic emission peaks of MMoO_4:Eu~(3+)(M=Sr,Ba)was changed as CTAB concentration and pH value changed.The emission spectra of MMoO_4:Eu~(3+)(M=Sr,Ba)could be adjusted by CTAB concentration and pH value due to their impacts on the structure.It was important that the different morphologies and photoluminescent properties of MMoO_4:Eu~(3+)(M=Sr,Ba)could be obtained by the facile hydrothermal method and modulated by changing CTAB concentration and pH value.     

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.