A dual-mode optical thermometer based on dual-excitation Bi^(3+),Sm^(3+)co-doped Y_(4)GeO_(8) phosphors

Dual-excitation and dual-emission Y_(4)GeO_(8):Bi^(3+),Sm^(3+)phosphors were manufactured by traditional solidphase sintering technique.The X-ray diffraction,morphology,photoluminescence,energy transfer process and temperature sensing properties of Y_(4)GeO_(8):Bi^(3+),Sm^(3+)samples were comprehensively evaluated.The Y4GeO_(8):Bi^(3+),Sm^(3+)phosphors exhibit characteristic emissions of Bi^(3+)(^(3)P_(1)→^(1)S_(0)) and Sm^(3+)(^(4)G_(5/2)→^(6)H)under both 290 and 347 nm excitations.In fluorescence intensity ratio and Commission International de L'Eclairage coordinates modes,Y_(4)GeO_(8):Bi^(3+),Sm^(3+)samples present excellent temperature measurement performance.The maximum relative sensitivity(S_(r-max)) values of the former are 1.55%/K(460 K,290 nm excitation) and 0.82%/K(506 K,347 nm excitation).The S_(r-max)(x) values of the latter are 0.21 %/K(437 K,290 nm excitation) and 0.15%/K(513 K,347 nm excitation).These results illustrate that Y_(4)GeO_(8):Bi^(3+),Sm^(3+)phospho rs can be used as a candidate material for a dual-mode optical thermometer under dual-excitation.

Quenching Study on Iron Impurity in Eu^(2+), Dy^(3+) Doped Strontium Aluminate Phosphor Prepared by Nano-Coating Process

A series of long afterglow phosphors, Eu2+, Dy3+, with different iron content were prepared by nano-coating process. The resulted precursors were characterized by Transmission Electron Microscope (TEM), which suggested that the precursor particles had nanometer size distribution. The optical quenching of iron impurity on the phosphor powders were investigated by X-Ray powder Diffraction (XRD) and photoluminescence methods. The XRD indicates that a pure monoclinic SrAl2O4∶Eu2+, Dy3+ was formed at 1200 ℃ and iron impurity up to 296.36×10-4% had no effect on the SrAl2O4∶Eu2+, Dy3+ phase structure. However, the luminescence intensity were strongly dependent on the trace iron impurity, which might be explained that iron displace the aluminium and form Fe-O bond, which competed energy with Eu2+ and transfer red them to infrared sites.

稀土离子掺杂CaY_(1-x)AlO_(4):xRE^(3+)(RE=Dy,Ho,Sm,Tm)荧光材料的发光性能

采用溶胶凝胶法合成稀土离子掺杂Ca Y_(1-x)Al O_4∶xRE^(3+)(RE=Dy,Ho,Sm,Tm)荧光粉。采用X射线粉末衍射仪(XRD)、高分辨率透射电镜(TEM)和荧光分光光度计(PL)分别对荧光粉的物相结构、形貌以及荧光性能进行表征。研究结果表明,所合成样品为四方晶系结构的纳米级材料,在紫外光激发下,掺杂离子均表现出特征的f-f电子跃迁发射,当Dy^(3+)、Ho^(3+)、Sm^(3+)和Tm^(3+)的掺杂摩尔分数分别为0.03,0.015,0.015,0.02时,样品发光强度最大,分别发射出白光、绿光、橙光和蓝光。

Preparation and characterization of flower-like SrAl_2O_4:Eu^(2+),Dy^(3+) phosphors by sol-gel process

A flower-like Eu^2＋ and Dy^3＋ co-doped SrAl2O4 long-lasting phosphorescent （LLP） phosphor was synthesized via the inorganic- salt-based sol-gel method. The crystal structure, morphology and optical properties of the composite were characterized. X-ray diffraction diffusion （XRD） data and DSC-TG curves of the phosphor revealed that the SrAl2O4 crystallites have been formed after the precursor was calcined at 900 ℃ and to be single-phase SrA1204 at 1100 ℃. The SEM photographs indicated that the sample exhibited a universal flower-like morphology with crystallite size of about l-2μm. After being irradiated with ultraviolet （UV） light, the flower-like phosphor emitted long-lasting green phosphorescence with an excitation peak at 365 nm and emission peak at 500 nm which was ascribed to the characteristic 5d-4f transition of Eu^2＋. Both the PL spectra and the luminance decay curve revealed that this phosphor exhibited efficient luminescence and long lasting properties.

Effect of Eu^(3+) doping on luminescence properties of a KAlSiO_(4):Sm^(3+) phosphor

This study presents the photoluminescence characteristic analysis of a series of red phosphors of KAlSiO_(4):1.5 mol%Sm^(3+),x mol%Eu^(3+)(x=2,3,4,5,6,7)prepared via high-temperature solid-phase reaction.The results show that the X-ray diffraction(XRD)refinement results are reliable.The unit cell parameters and volume gradually decrease as the Eu^(3+) concentration increases,resulting in a grain size reduction of 10.22%.When x=6,the emission peaks of Sm^(3+) at 564,601,and 651 nm disappear completely,and the corresponding full width at half maximum becomes 0.At 610 nm,the emission peak intensity of Eu^(3+) is increased by a factor of 4.8.The resonant non-radiative energy transfer effect is greater than the co-excitation effect.A maximum energy transfer efficiency of 97.8%is achieved.The integral area at 610 nm is as high as 85%.The color purity of the phosphor is as high as 92.97%,and the internal quantum yield gradually changes from 32%to 51%.Ultimately,these results confirm that the silicate phosphor is suitable for the red component in the three primary color phosphors of white light-emitting diodes.

Luminescence properties of phosphate phosphors Ba3Gd1-x(PO4)3：xSm^3＋

A series of reddish orange phosphors Ba3Gd1-x（PO4）3：xSm^3＋ （x = 0.02, 0.04 0.12） were prepared by the high-temperature solid-state reaction. X-ray powder diffraction （XRD） and diffuse reflectance and photoluminescence spectra were utilized to characterize the structure and spectral properties of the phosphors. The phosphors have strong absorption in the near-UV region. CIE chromaticity coordinates of the phosphors are located in the reddish orange region since the strongest emission band is around 598 nm and related to the 4G5/2 - 6H7/2 transition of Sm^3＋. Optimal concentration of Sm^3＋ in the phosphors is about 6.0 at%. The quantum yield of the Ba3Gdo.94（PO4）3：0.06Sm^3＋ under excitation at 403 nm is about 52.07%. Temperature dependent photoluminescence spectra of the Ba3Gdo.94（PO4）3：0.06Sm^3＋ were measured and the phosphor exhibits high thermal stability of emission. All the results show that the Ba3Gd（PO4）3：Sm^3＋ phosphor may be a potential red phosphor for near-UV based white LEDs.

Photoluminescence properties and energy transfer of novel orange–red emitting phosphors:Ba_(3)Bi_(2)(PO_(4))_(4):Sm^(3+),Eu^(3+) for white light-emitting diodes

Sm^(3+), Eu^(3+)co-coped Ba_(3)Bi_(2)(PO_(4))_(4) phosphors,as potential phosphors for white light-emitting diode applications, were synthesized through the solid-state reaction method for the first time. The crystal structure,absorption spectra, photoluminescence properties, decay time, energy transfer mechanism, temperature-dependent properties, and Commission International De L’Eclairage(CIE) chromaticity coordinates were investigated systematically. The pure eulytite-type Ba_(3)Bi_(2)(PO_(4))_(4) phase was obtained after heating at 980 ℃ for 5 h. A notably enhanced absorption efficiency at 393 nm was observed when Sm^(3+), as a sensitizer, was doped into Ba_(3)Bi_(1.82)(PO_(4))_(4): 0.18 Eu^(3+)and the band gap of the Ba_(3)Bi_(2)(PO_(4))_(4) host was estimated to be 4.19 eV. The emission intensity of Ba_(3)Bi_(1.82)(PO_(4))_(4): 0.18 Eu^(3+)was significantly enhanced when Sm^(3+)was co-doped. The existence and mechanism of energy transfer from Sm^(3+) to Eu^(3+)were evaluated by photoluminescence spectra and decay time measurements. The CIE chromaticity coordinate of Ba3 Bi1.75(PO4)4: 0.07 Sm^(3+), 0.18 Eu^(3+) phosphor was calculated to be(0.5746, 0.4197), respectively.

Synthesis and optical properties of novel apatite-type NaCa_(3)Bi(PO_(4))_(3)F:Dy^(3+)yellow-emitting fluorophosphate phosphors for white LEDs

In this study,novel yellow-emitting fluorophosphate NaCa_(3)Bi(PO_(4))_(3)F phosphors doped with different concentrations of Dy^(3+)ions were first obtained via high-temperature solid-state reaction.The crystal structure,phase purity,particle morphology,photoluminescence(PL)properties,thermal stability,and luminescence decay curves of the resulting phosphors were then characterized in detail.Under the excitation of 349 nm,the three dominant peaks of the NaCa_(3)Bi(PO_(4))_(3)F:Dy^(3+)are centered at 480 nm(^(4)F_(9/2)-^(6)H_(15/2)),577 nm(^(4)F_(9/2)-^(6)H_(13/2)),and 662 nm(^(4)F_(9/2)-^(6)H_(11/2)).The optimal doping concentration of Dy^(3+)ions in the NaCa_(3)Bi(PO_(4))_(3)F:xDy^(3+)phosphors is x=5 mol%.The phosphors show excellent thermal stability with high activation energy(Ea=0.32 eV).Eventually,the synthesized white lightemitting diode(w-LED)demonstrates the Commission International de L’Eclairage(CIE)chromaticity coordinates of(0.341,0.334),a good correlated color temperature(CCT)of 5083 K,and a high color rendering index(Ra)of 92.Revealing its potential as yellow-emitting phosphors,the feasibility of the fabricated apatite-type NaCa_(3)Bi(PO_(4))_(3)F:Dy^(3+)fluorophosphate phosphors was confirmed for wLEDs.

Photoluminescence properties and energy transfer of a single-phased white-emitting NaAlSiO_4:Ce^(3+),Sm^(3+)phosphor

A series of tunable phosphors NaAlSiO_4：Ce^（3＋）,Sm^（3＋） were synthesized using a conventional high-temperature, solid-state method. Crystal structure, photoluminescence excitation, and emission spectra with fluorescence decay curves were investigated. Under UV excitation（325 nm）, NaAlSiO_4：Ce^（3＋）,Sm^（3＋） showed strong blue emission located at 444 nm and orange-reddish emission centered at 563, 601, 648 and 712 nm, stemming from the characteristic emission for 4f-5d transition of Ce^（3＋） and ~4G_（5/2）→~6H_J（J=5/2, 7/2, 9/2, 11/2） transition of Sm^（3＋）, respectively. In addition, we studied the detailed energy transfer process between Ce^（3＋） and Sm^（3＋） and found that it belonged to dipole-dipole resonance energy transfer. Furthermore, we noted that the white light emitting from the Ce^（3＋）, Sm^（3＋） co-doped phosphors with the color coordinate（x=0.313, y=0.283） could be observed under 325 nm excitation, which was close to the ideal white light（x=0.33, y=0.33）. The results indicated that this phosphor has a potential application as a single-phased alumino-silicate phosphor for ultraviolet white light-emitting diodes（UV-WLEDs）.

A novel white emitting phosphor Ca_2PO_4Cl:Dy^(3+): luminescence, concentration quenching and thermal stability

A novel white emitting phosphor Ca2PO4Cl：Dy^3＋ was synthesized by a solid state method. The luminescence, concentration quenching and thermal stability of Ca2PO4Cl：Dy^3＋ were investigated. Ca2PO4Cl：Dy^3＋ showed three emission peaks, which were located at 483, 575 and 660 nm. Though the ratio of yellow to blue emission intensities showed a similar value, the intensities of yellow and blue peaks were influenced by Dy^3＋ concentration, and the concentration quenching effect was observed. The emission intensity of Ca2PO4Cl：Dy^3＋ as a function of temperature was explored and the emission intensity（at 150 °C） of Ca2PO4Cl：Dy^3＋ was 90.0% of the value at 25 °C, and activation energy was 0.18 eV. The results indicated that Ca2PO4Cl：Dy^3＋ might be conducive to development of white LEDs.

KAlSiO_(4)∶Re^(3+)(Re=Dy/Sm)荧光粉的能量传递机理

采用高温固相法制备了一系列Dy^(3+),Sm^(3+)共掺杂的KAlSiO_(4)荧光粉材料。实验结果表明,少量Dy^(3+),Sm^(3+)的掺入没有改变KAlSiO_(4)的晶体结构。当用Dy^(3+)的特征激发波长激发KAlSiO_(4)∶1%Dy^(3+),w%Sm^(3+)时,发射光谱显示,样品中存在从Dy^(3+)到Sm^(3+)的共振非辐射能量传递,同时色坐标移动很小,并发生了528 nm处的红移和713 nm处的蓝移现象;当用Sm^(3+)的特征激发波长激发KAlSiO_(4)∶1.5%Sm^(3+),v%Dy^(3+)时,发射光谱与KAlSiO_(4)∶1.5%Sm^(3+)发射光谱相似,没有出现Dy^(3+)的特征发射峰,但Sm^(3+)在651 nm处的发光强度提高了6.5倍。这说明没有发生从Sm^(3+)到Dy^(3+)的能量回传,Dy^(3+)的引入促进了晶格的匹配,使得Sm^(3+)的发光强度得到大幅增强。通过理论计算得出从Dy^(3+)到Sm^(3+)的能量传递效率最高可达52%,能量传递相互作用是电四级-电四级相互作用。荧光粉的色坐标均在(0.41,0.51)附近,位于黄绿色区域。386 nm激发下的内量子产率从25.8%逐渐提高到42.6%。

Samarium doped apatite-type orange-red emitting phosphor Ca5（PO4）2SiO4 with satisfactory thermal properties for n-UV w-LEDs

A novel single-phase Sm^3+activated Ca5(PO4)2SiO4 phosphor was successfully fabricated via a conventional solid-state method,which can be e fficie ntly excited by near ultraviolet(n-UV)light-emitting chips.The crystal structure and luminescence properties were characterized and analyzed systematically by using relevant instruments.The Ca5(PO4)2SiO4:Sm^3+phosphor shows an orange-red emission peaking at600 nm under the excitation of 403 nm and the optimal doping concentration of Sm^3+is determined to be 0.08,The critical distance of Ca5(PO4)2SiO4:0.08 Sm^3+is calculated to be 1.849 nm and concentration quenching mechanism of the Sm^3+in Ca5(PO4)2SiO4 host is ascribed to energy transfer between nearestneighbor activators.The decay time of Ca5(PO4)2 SiO4:0,08 Sm^3+is determined to be 1.1957 ms.In addition,the effect of temperature on the emission intensity was also studied,72.4%of the initial intensity is still preserved at 250℃,better thermal stability compared to commercial phosphor YAG:Ce^3+indicates that Ca5(PO4)2SiO4:0.08 Sm^3+has excellent thermal stability and active energy is deduced to be 0.130 eV.All the results demonstrate that orange-red emitting Ca5(PO4)2SiO4:0.08 Sm3+phosphor exhibits good luminescent properties.Owing to the excellent thermal quenching luminescence property,Ca5(PO4)2SiO4:0.08 Sm^3+phosphor can be applied in n-UV white light emitting diodes and serve as the warm part of white light.