Effect of electron traps on long afterglow behavior of Sr3Al2O6:Eu0.012+,Dy0.02-x3+,Hox3+

The long persistent phosphors Sr3Al2O6:Eu0.012+,Dy0.02-x3+,Hox3+ (x=0, 0.01, 0.02) were prepared by a high temperature solid state reaction. All samples showed a broad band emission peaking at ~510 nm, which could be ascribed to Eu2+ transition between 4f65d1 and 4f7 electron configurations. With the increase of substitution of Ho3+ ions for the Dy3+ ions in the as-prepared phosphors Sr3Al2O6:Eu0.012+,Dy0.02-x3+,Hox3+ (x=0, 0.01, 0.02), the initial intensity of the afterglow obviously decreased. From the thermoluminescence (TL) curves of the samples, we concluded that codoped Ho3+ ions led to a decline of the trap depth and redistribution of the trap. This may be responsible for the change of afterglow of Sr3Al2O6:Eu0.012+,Dy0.02-x3+,Hox3+ (x=0, 0.01, 0.02).     

SrAl2O4 :Eu2+, Dy3+ Long Afterglow Phosphors Prepared by Chemical Coprecipitation Method

SrAl2 O4: Eu2 , Dy3 long afterglow phosphors were prepared by chemical coprecipitation method. Ammonium carbonate and ammonium hydrogen carbonate were used as the precipitants. The preparation of the SrAl2 O4: Eu2 ,Dy3 precursor was completed at room temperature by controlling the concentration of the metal-salt solution, pH value of the system, etc. The phosphors were prepared by sintering the precursor at 1000 ～ 1200 ℃ in a weak reducing atmosphere for 2 h. The XRD, SEM, excitation spectra, emission spectra and afterglow decay of the samples were tested and the optimal synthesis conditions of the SrAl2O4: Eu2 , Dy3 long afterglow phosphors prepared by precipitation method were determined. The phosphor which had good luminescent properties is prepared and its persistent time can reach more than 1600 min. In the coprecipitation process, a small amount of glucose operates to refe the luminescent powders. The particle size of the phosphor can be less than 1 μm. The sintering temperature of the sample prepared by the coprecipitation method is much lower than that of the one prepared by the high temperature solid state method.Compared with the high temperature solid state method, a clear blue shift occurs in the excitation and emission spectra of the samples.     

A novel long lasting phosphor Sr5 （PO4）3FxCll_x：Eu2＋,Gd3＋ prepared in air condition

A series of blue long afterglow mixed halide-phosphate phosphors Sr5 （PO4）3 FxCll-x：Eu2＋,Gd3＋ were synthesized in air by traditional solid-state reaction routte. The crystal structures, photoluminescence, thermolurninescenee properties and afterglow proper- ties of the phosphors were characterized systematically using X-ray diffraction （XRD）, luminescence spectrophotometer, microcom- puter thermoluminescence dosimeter and single photon counter, respectively. Under 280 nm excitation, the broadband emissions of Eu2＋ ions were observed at 445 nm （blue） due to the 4f7→4f65d transition. It was demonstrated that there existed the self-reduction of the Eu3＋ to Eu2＋ ions in this special halide-phosphate matrix in air condition. The addition of Gd3＋ ions obviously enhanced the after- glow properties of the single doped Eu2＋ ions in the halide-phosphate phosphors. And the content of the fluoride anions also had sig- nificant influence on the afterglow properties. All results indicated that Srs （PO4）3 FxCI1-x：Eu2＋,Gd3＋ might be potential phosphors for long lasting phosphorescence （LLP） materials.     

Long afterglow yellow luminescence from Pr3+ doped SrSc2O4

A yellow emitting long afterglow luminescence material SrSc₂O₄:Pr³⁺ was successfully prepared by solid state reaction method. SrSc₂O₄:Pr³⁺ phosphor shows a long afterglow luminescence peak at about 495, 545, 621, 630 and 657 nm, respectively, corresponding to the f–f transitions of Pr³⁺. The afterglow chromaticity coordinates of SrSc₂O₄:1 at%Pr³⁺ were calculated to be (0.35, 0.41), indicating that the afterglow emission is close to the light of yellow region. And, the afterglow luminescence of the optimal sample doped by 1 at%Pr³⁺ can persist for over 3 h. The thermoluminescence results suggest that there are three types of traps with depth of 0.61, 0.69 and 0.78 eV exiting for all the samples, which are produced by the addition of Pr³⁺ ions. The trap density of SrSc₂O₄:1 at%Pr³⁺ is the maximum when the incorporation of Pr³⁺ ions reaches 1 at%, which thus results in the longest afterglow luminescence. All the results indicate that SrSc₂O₄:Pr³⁺ can be a potential candidate of novel long afterglow phosphors.     

Effect of mixing process on the luminescent properties of SrAl_2O_4:Eu~(2+),Dy~(3+) long afterglow phosphors

A new mixing method was developed for solid-state reaction synthesis of SrAl2O4:Eu2+,Dy3+ long afterglow phosphors.The morphology and crystal structure of the phosphors were analyzed with scanning electron microscope(SEM) and X-ray diffractometer(XRD).The excitation and emission spectra of the long afterglow phosphors were measured,and the main emission band was around 514 nm.The decay time of the product was measured and compared with the phosphors prepared using dry-mixing method and wet-mixing method.It ...     

稀土长余辉发光材料的开发应用与改性处理

介绍了以铝酸盐为基质以铝酸盐为基质稀土为激活剂或主激活剂的新型光致长余辉的特点、开发现状、应用领域及蓄光机理。重点综述了将蓄光体制成性能优良的发光树脂、发光陶瓷、着色蓄光性复合体及用作灯粉时的改性处理工艺、产品特点和用途。     

Synthesis of Long Afterglow Phosphors MAl2O4:Eu2+, Dy3+(M=Ca, Sr, Ba) by Microemulsion Method and Their Luminescent Properties

Long afterglow phosphors MAl2O4:Eu2 , Dy3 (M=Ca, Sr, Ba) were synthesized by microemulsion method, and their crystal structure and luminescent properties were compared and investigated. XRD patterns of samples indicate that phosphors CaAl2O4:Eu2 , Dy3 and SrAl2O4:Eu2 , Dy3 are with monoclinic crystal structure and phosphor BaAl2O4:Eu2 , Dy3 is with hexagonal crystal structure. The wide range of excitation spectrum of phosphors MAl2O4:Eu2 , Dy3 (M=Ca,Sr,Ba) indicates that the luminescent materials can be excited by light from ultraviolet ray to visible light and the maximum emission wavelength of phosphors MAl2O4:Eu2 , Dy3 (M=Ca, Sr, Ba) is found mainly at λem of 440 nm (M=Ca), 520 nm (M=Sr) and 496 nm (M=Ba) respectively, the corresponding colors of emission light are blue, green and cyna-green respectively. The afterglow decay tendency of phosphors can be summarized as three processes: initial rapid decay, intermediate transitional decay and very long slow decay. Afterglow decay curves coincide with formula I=At-n, and the sequence of afterglow intensity and time is Sr＞Ca＞Ba.     

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.     

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.     

Luminescent properties of blue long-lasting phosphorescence phosphors Sr6Al18Si2O37：Eu2＋,RE3＋

A series of novel blue long-lasting phosphorescence phosphors Sr6A118Si2037：Eu^2＋,RE^3＋ （RE3＋=Ho^3＋, Gd^3＋, Dy^3＋ and Pr^3＋） were prepared by the conventional high-temperature solid-state reaction in a reductive atmosphere. Their properties were systemati- cally investigated utilizing X-ray diffraction （XRD）, photoluminescence, phosphorescence and thermoluminescence （TL） spectra. The phosphors emitted blue light that was related to the emission of E~＋ due to 5d-4f transition. Bright blue long-lasting phosphorescence （LLP） could be observed after the excitation source was switched off. For the optimized sample, the blue long-lasting phosphores- cence could last for nearly 4 h in the light perception of the dark-adapted human eye （0.32 mcd/m2）. The effects of RE3＋ ions on phosphorescence properties of the phosphors were studied, and the results showed that the co-doping of RE^3＋ ions greatly enhanced the intensity of the peak around 315 K which was related to the long lasting phosphorescence of the phosphors at room temperature and consequently improved the performance of the blue phosphorescence such as intensity and persistent time.     

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.     

Enhancement of luminescence and afterglow in Ca0.8Zn0.2TiO3:Pr3+ by Nb5+ substitution for Ti4+

Nb5+ doped Ca0.8Zn0.2TiO3:Pr3+ red long afterglow phosphors were synthesized by solid-state reaction methods. X-ray diffraction, photoluminescence spectroscopy and thermally stimulated spectrometry were used to investigate the effects of Nb5+ content on the crystal characteristics and luminescent properties of Ca0.8Zn0.2Ti1-xNbxO3:Pr3+ phosphors. The results showed that the addition of a small quantity of Nb5+ had negligible effect on the crystal characteristics of Ca0.8Zn0.2Ti1-xNbxO3:Pr3+, but it could change the trapping parameters (the depth of trap, frequency factors and the concentration of trapped charges at t=0) of Ca0.8Zn0.2Ti1-xNbxO3:Pr3+ phosphors, and then led to the enhance-ment of red fluorescence and phosphorescence at 612 nm originating from 1D2→3H4 transition of Pr3+. Both of the red fluorescence intensity and afterglow time reached the largest values in the sample of Ca0.8Zn0.2Ti1-xNbxO3:Pr3+ with x=0.05. The afterglow time of Ca0.8Zn0.2Ti0.95Nb0.05O3:Pr3+ phosphors lasted for over 24 min (≥1 mcd/m2) when the excited source was cut off.     

Co-Precipitation Synthesis and Spectral Characteristics of Long Afterglow Phosphor Y2O2 S： Sm^3＋, Mg^2＋ , Ti^4＋

Y2O2S：Sm^3＋, Mg^2＋, Ti^4＋ phosphor was synthesized by co-precipitation method. The crystalline structure of all synthesized phosphors was investigated by XRD. The result showed that all synthesized phosphors had a hexagonal crystal structure, which was the same as Y2O2S. The emission spectrum and excitation spectrum were measured, and the effect of Sm^3 ＋ molar ratio on the spectra was discussed. The emission spectra of the phosphors showed three emission peaks due to typical transitions of Sm^3 ＋ （4G5/2→6HJ ,J = 5/2, 7/2, 9/2）, and the emission peaks at 606 nm was stronger than others. With the increase of Sm^3 ＋ molar ratio, the emission intensity was strengthened. The excitation peaks were ascribed to the representative energy transition 4f→4f of Ti^4＋ phosphor prepared by co-precipitation method was Sm^3＋ ions. The results indicated that the Y2O2S ： Sm^3＋ , Mg^2＋ , an efficient long afterglow phosphor.     

Synthesis of Long Afterglow Phosphor CaAl2Si2O8:Eu2+, Dy3+ via Sol-Gel Technique and Its Optical Properties

The long afterglow phosphor CaAl2Si2O8:Eu2 , Dy3 was prepared by a sol-gel method. The sol-gel process and the structure of the phosphor were investigated by means of X-ray diffraction analysis (XRD). It is found that the single anorthite phase formed at about 1000 ℃, which is 300 ℃ lower than that required for the conventional solid state reaction. The obtained phosphor powders are easier to grind than those of solid state method and the partical size of phosphor has a relative narrow distribution of 200 to 500 nm. The photoluminescence and afterglow properties of the phosphor were also characterized. An obvious blue shift occurs in the excitation and emission spectra of phosphors obtained by sol-gel and solid state reaction methods. The change of the fluorescence spectra can be attributed to the sharp decrease of the crystalline grain size of the phosphor resulted from the sol-gel technique.     

Preparation and Luminescence Properties of the New Long Phosphorescent Phosphors Ba1-xCaxAl2O4∶Eu2+,Dy3+

New long phosphorescent phosphors Ba1-xCaxAl2O4∶Eu2 , Dy3 with tunable color emission were prepared and studied. The emission spectra show that the tuning range of the color emission of the phosphors is between 498 and 440 nm, which is dependent on x, under the excitation of UV. The wavelength of the afterglow increases with the increasing of x until x equals 0.6. The XRD patterns show that the single phase limit in the phosphors is below x value of 0.4. The Thermoluminescence spectra were measured to investigate the traps created by the doping of Dy3 .     

A novel Gd-based phosphor NaGdGeO4:Bi3+,Li+ with super-long ultraviolet-A persistent luminescence

In very recent years,ultraviolet(UV) persistent luminescent materials(PLMs) have attracted widespread attention due to their potential biological applications.However,owing to the lack of suitable emitters and hosts,the design and development of excellent UV PLMs remain challenging.Here,we report a new Gd-based PLM NaGdGeO₄:Bi³⁺ with super-long UVA persistent luminescence(PersL).By further codoping Li⁺ ions to increase the concentration of traps,the UVA PersL int...     

The effect of phosphor persistence on image quality in digital x-ray scanning systems

A digital x-ray scanning system offers several advantages over conventional film-screen systems. However, there are sources of image degradation resulting from the scanning motion, such as motion blur due to the temporal response of the phosphor. This mechanism produces an asymmetrical blur, requiring the use of the complex optical transfer function (OTF) rather than the normal modulation transfer function (MTF) for correct characterization of image resolution. The luminescence response of eight phosphors was measured under pulsed x-ray excitation. A weighted exponential model was used to represent the primary luminescence. The dominant luminescence life-times ranged from 2.7 microseconds for Gd2O2S:Pr to 558 microseconds for Gd2O2S:Tb. The long term response was also measured, monitoring significant increases in a slow form of luminescence known as afterglow. Afterglow was modeled by an inverse power law equation. Afterglow was found to be strong in two of the phosphors studied (ZnCdS:Ag and YTaO4). In selecting a phosphor for a scanning system, it must satisfy several criteria, including a fast temporal response. Thus, a phosphor like Gd2O2S:Tb, which has a slow luminescence, but otherwise excellent imaging properties, may not be as useful as a more rapid phosphor like CsI:Tl.     

Enhanced afterglow performance of CaAl_2O_4:Eu~(2+),Nd~(3+) phosphors by co-doping Gd~(3+)

In order to effectively improve the afterglow properties of CaAl_2 O_4:Eu~(2+),Nd~(3+) phosphors,a series of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_2 O_4:0.012 Eu~(2+),0.006 Nd~(3+),xGd~(3+)phosphors belong to monoclinic CaAl_2 O_4,without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4 f~65 d→4 f~7 transition of Eu~(2+) ions.Doping with appropriate amount of Gd~(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd~(3+) induces the fluorescent quenching.The doping of moderate Gd3+changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.     

稀土纳米荧光粉显现潜指纹研究进展

稀土纳米荧光粉用于潜指纹可视化,利用了稀土荧光粉发光强度高和纳米粉体与潜指纹具有适宜的附着力特性,显示的潜指纹具有高对比度、高质量和高强度的荧光,特别是上转换纳米荧光粉和长余辉纳米荧光粉显示潜指纹能消除背景干扰,然而用紫外光激发的稀土荧光粉受到基底背景颜色和强背景自发荧光的干扰,在潜指纹显现方面应用具有局限性。本文综述了荧光粉合成方法、形貌、粒度和结构以及各种荧光粉对显示潜指纹特征脊细节级别的影响,特别是继续开发发光强度高、背景干扰小、适应各种基底表面显示潜指纹的稀土纳米荧光粉仍然是一个挑战。     

Effects of Host Doping on Spectral and Long-Lasting Properties of Sm^3＋ -Doped Y2O2S

Gd- or Lu-doped long afterglow red phosphor Y2O2S：Sm^3＋ was synthesized using the high temperature flux fusion method. The obtained phosphors were analyzed using X-ray diffraction to determine the crystal structure, and the phase analyses show that the product is in single phase. The luminescence spectra and decay curve were measured on a Hitachi F-4500 fluorescence spectrophotometer. The decay time was determined on an ST-900PM weak light photometer. The analyses show that host doping of Lu improves both luminescence and decay time of the materials. The concentration of doped Lu and Sm was varied in order to determine the optimal condition and to synthesize the product with the best properties. The mechanism of the long afterglow was also briefly discussed.