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.     

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+).     

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.     

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.     

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.     

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 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.     

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%.     

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.     

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.     

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.     

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.     

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.     

Luminescent Properties of Eu~(3+) and Bi~(3+) and Their Interaction in LaBO_3 and GdBO_3

Under the excitation of UV light and cathode ray,the dependence of the excitation and emission spectraand luminescent lifetime of Eu~(3+)and Bi~(3+)on composition and structure in LABO_3 and GdBO_3 has been stu-died.The results indicate that the emission spectra of Eu~(3+)in LaBO_3 with aragonite structure and in GdBO_3with YBO_3 structure are quite different.Under 254 nm excitation,Eu~(3+)emission is sensitized by Bi~(3+)inGdBO_3 matrix.In other case Eu~(3+)emission is quenched by Bi(3+).     

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.     

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.     

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.     

Controllable synthesis of Eu~(3+) ions doped Zn(OH)F and ZnO micro-structures:Phase,morphology and luminescence property

Eu~(3+) ions doped Zn(OH)F and ZnO micro-structures with specific morphologies were synthesized by a simple hydrothermal method only through altering the addition amount of NH_4F and hexamethylenetetramine(HMT). The phase structure, morphology and luminescence properties of the as-prepared samples were characterized by X-ray powder diffraction(XRD), scanning electron microscopy(SEM),transmission electron microscopy(TEM), photoluminescence(PL) spectra and lifetime. The results indicate that the obtained Zn(OH)F:Eu~(3+) samples possess net-like and dandelion-like morphologies,which have an identical orthorhombic phase structure. It is found that the addition amount of raw materials such as NH_4F and HMT plays a critical role for the formation of Zn(OH)F:Eu~(3+). If the addition amounts of NH_4F or HMT are reduced by half, the hexagonal ZnO:Eu~(3+) sample with peanut-like morphology can be obtained. Under the excitation of UV light, both the as-prepared Zn(OH)F:Eu~(3+)and ZnO:Eu~(3+) samples exhibit the characteristic emission of the doped Eu~(3+).     

Photoluminescence properties of Eu~(3+)-doped MgAl_2O_4 nanoparticles in various surrounding media

Eu~(3+)-doped MgAl_2O_4 nanoparticles were prepared by modified Pechini method.X-ray diffraction analysis shows pure tetragonal spinel phase without any impurities.The average size of synthesized nanoparticles was determined to be about 50-60 nm using scanning electron microscopy and static light scattering techniques.Emission and excitation spectra as well as lifetimes of MgAl_2O_4:Eu~(3+) nanophosphors were explored in surrounding media with different refractive indexes.Surrounding medium does not affect luminescence bands position,whereas ~5D_0 lifetime monotonically decreases along with increase of medium refractive index.Effect of surrounding media on radiative and nonradiative decay rates,which were calculated using 4f-4f intensity theory,was studied and discussed.Filling factor of prepared nanoparticles is defined using both radiative and observed lifetimes.