Longer Afterglow Time Research Articles

Preparation of Zn3Ga2Ge2O10:Cr3+, Al3+ nanometer phosphors via sol-gel method

In this paper, the near-infrared luminescence Zn3Ga2Ge2O10:Cr3+, Al3+ prepared by citrate sol-gel method is studied. When the Cr3+ doping amount is 0.01% and the Al3+ doping amount is 0.2, the prepared Zn3Ga2Ge2O10: The afterglow properties of Cr3+, Al3+ afterglow nanomaterials are the best. The sample has the least heterogeneous phase, the highest crystallinity, the longest afterglow time, the excitation peak at 267 nm and the emission peak at 745 nm. The light produced belongs to the wavelength range of near-infrared light. After excitation with an ultraviolet lamp, the material can see deep cherry red light in the dark.

Novel white-emitting afterglow phosphor Na2CaSn2Ge3O12:Dy3+: Preparation, photoluminescence, and phosphorescence properties

Afterglow was found in germanate (Na2CaSn2Ge3O12) doped with Dy3+ phosphor, which was prepared at 1250 °C through the traditional solid-state reaction in air. Na2CaSn2Ge3O12:Dy3+ phosphors were comprehensively characterized by XRD, photoluminescence excitation and emission spectra, thermo-luminescence and long persistent phosphorescence decay curves to study the effects of the Dy3+ concentration on their properties. The XRD results indicates that a single phase of Na2CaSn2Ge3O12 can be obtained. Upon excitation by 248-nm UV light, all samples emit white light, which is composed of yellow and blue originating from the Dy3+ (4F9/2→6HH/2, H = 11, 13, 15 transition). The Na2CaSn2Ge3O12:Dy3+ phosphor exhibited the perfect luminescent property and longest afterglow time when the Dy3+ concentration was 0.6 mol%. The CIE chromaticity coordinates for Na2CaSn2Ge3O12:Dy3+ were (0.3916, 0.3914). From the long persistent phosphorescence decay curve of the Na2CaSn2Ge3O12:Dy3+ phosphor, it was concluded that this process contains a fast and a slow decay. The afterglow luminescence from the Na2CaSn2Ge3O12:Dy3+ phosphor persisted for more than 7.8 h after irradiation with ultraviolet lamp. The Na2CaSn2Ge3O12:Dy3+ phosphor is deemed to be a potential storage phosphor that can be applied in the field of practical application. After incorporation of Dy3+ into the Na2CaSn2Ge3O12 matrix, new foreign traps (DyCa°, DyNa°°) were produced, and the concentration of internal traps (VCa″, VNa′) increased approximately 10 times. The luminous mechanism of the Na2CaSn2Ge3O12:Dy3+ phosphor was studied.

Luminescence decay evaluation of long-afterglow phosphors

In the current study, the phosphorescence decays of the long-afterglow materials of SrAl2O4:Eu, Dy, Sr4Al14O25:Eu, Dy, Sr2MgSi2O7:Eu, Dy, and ZnS:Cu, Co have been measured over long time (15h to 16h). The evaluation methods of luminescence decay are analyzed and summarized. The existing formulas are in accordance with the experimental decay data in the initial fast decay stage. However, the deviation is much larger and the accuracy is much lower in the slow decay stage. Therefore, the existing formulas cannot be used to accurately describe the luminescence decay of the samples with much longer afterglow time (>80min). Moreover, certain formulas do not match the actual decay situation of long-afterglow luminescence. We suggest our solutions for this problem.

Effect of RE<sup>3+</sup> Codopant on Afterglow Time of SrS:Eu<sup>2+</sup>,RE<sup>3+</sup><sup></sup>

The longest afterglow time of an orange-red- emitting SrS:Eu2+,Pr3+ afterglow phosphor by visible light irradiation was about 1010 minutes was previously achieved by varying the synthetic conditions such as amount of Li+ added, reduction temperature, reduction time, and initial Eu/Sr and Pr/Sr atomic ratios in previous paper. Therefore, this study reports on the effect of the RE3+ codopants on the afterglow time of an orange-red-emitting SrS phosphor by visible light irradiation. SrSO4:Eu3+,RE3+(RE3+ = Tm3+, Er3+, Tb3+, Nd3+, Pr3+, Ce3+, and La3+), which was the precursor for SrS phosphors, was synthesized via a liquid-phase reaction. SrSO4:Eu3+,RE3+ was pressurized at 10 MPa for a few minutes to form a compact, which was then heated under a H2S or Ar-H2 (5 mol%) reductive atmosphere at 1400 °C for 2.5 h to generate the SrS:Eu3+,RE3+ afterglow phosphor. The emission color of the SrS:Eu2+,RE3+ afterglow phosphor was orange-red and its emission peak was observed around 610 nm. The excited band of the phosphor was in the range of visible light more than 440 nm. The emission and excitation spectra of the SrS:Eu2+,RE3+ afterglow phosphor were not dependent on the RE3+ codopants. However, the afterglow time of SrS:Eu2+,RE3+ phosphor was increased with the increase of ionic radius of the coactivator. The longest afterglow time of SrS:Eu2+,Ce3+ phosphor by irradiating for 5 minutes at 1000 lx which was created from a D65 lamp was 1376 minutes. This was 9.5 times longer than that of a commercial available phosphor (CaS:Eu2+,Tm3+).

Efficient Luminescence of Long Persistent Phosphor Combined with Photonic Crystal

In this paper, the luminescence properties of the long persistent phosphor (LPP) were apparently improved by combining with photonic crystal (PC). An optimized PC can double the afterglow intensity and prolong 1.7 times of the afterglow time of SrAl2O4: Eu, a commercially available LPP, without any dopants. These results were ascribed to the stopband effect of the PC. The PC combined LPP structure was beneficial for the applications of LPP in emergency indication which called for brighter afterglow intensity and longer afterglow time.

Preparation and Properties of CdSiO<sub>3</sub>: Mn<sup>2+</sup>, Er<sup>3+</sup> Phosphor

CdSiO3: Mn2+, Er3+ long-lasting phosphor was prepared by the conventional high temperature solid-state method. Effects of the concentration of Mn2+ and Er3+ on the luminescent properties of phosphor CdSiO3: Mn2+, Er3+ were investigated by means of photoluminescence (PL) spectra and the afterglow intensity decay curves. It was found that when the Mn2+ and Er3+ dopant-concentrations were 0.2 mol% and 0.8 mol% of Cd2+ ions in CdSiO3, respectively, the luminescence of phosphor prepared had better luminescent property and longer afterglow time. The phosphorescence for it could be seen with the naked eye for more than 60 min in the dark after the removal of the 254 nm UV light. Role of Er3+ co-doped into CdSiO3: Mn2+ matrix was discussed in this paper.

Fabrication and Characterization of Calcium Silicate Phosphors - Ca<sub>2</sub>SiO<sub>4</sub> and Ca<sub>2</sub>MgSi<sub>2</sub>O<sub>7</sub> -

Calcium silicate phosphors, Ca2-xSiO4(CS):Eu3+x, CS:Eu2+x and Ca2-y-zMgSi2O7 (CMS):Eu2+y,Dy3+z were prepared by the solid state reaction. The phases in CS:Eu3+ system were β- and αL’ -types. The fluorescent color under a black-light irradiation was red and the emission spectrum consisted of 590nm(αL’), 615nm(β) and 625nm(αL’) peaks. The emission intensity took a maximum value at x=0.2. The addition of B3+ accelerated the solid solution of Eu3+. The phase in CS:Eu2+ system was β-type only. The fluorescent color was yellow-green(520nm). The emission intensity took a maximum value at x=0.01. The CMS product showed the akermanite phase. The lattice constants of CMS:Eu2+ increased with increasing Eu content, but those became constant at y>0.05. The fluorescent color of CMS:Eu2+ was yellow-green and the emission intensity took a maximum value at y=0.03. In the case of CMS:Eu2+0.03,Dy3+z, the fluorescent color and the afterglow color were same, yellow-green. The emission intensity took a maximum value at z=0.06. The longest afterglow time, 23min., was obtained at z=0.09. The trap depth were 0.64-0.69 eV.

EFFECT OF REDUCING ATMOSPHERE ON THE AFTERGLOW PROPERTIES OF RED-EMITTING CaS:Eu2+,Pr3+ PHOSPHORS

The afterglow time of typical red-emitting phosphors is much shorter than those of green- or blue-emitting phosphors which afterglow time were longer than 1000 min. CaS has been used as an effective host material for afterglow phosphors because trapping centers can be easily created in the host by doping with an activator. This study reports on the effect of a reducing atmosphere on the afterglow properties of a red-emitting CaS:Eu2+,Pr3+ phosphor. The phosphor was prepared by reduction under an Ar-H2 (5%) or H2S atmosphere from a CaSO4:Eu3+,Pr3+ phosphor prepared using a liquid phase method. Heating the CaSO4:Eu3+,Pr3+ phosphor for 2 h under an Ar-H2 (5%) atmosphere at 1050°C gave CaO as by-product in addition to CaS . The resulting phosphor exhibited red-emission at 646 nm originating from Eu2+ ions upon visible light irradiation, and gave some afterglow after cessation of visible light irradiation. Addition of Li+ ions extended the afterglow time of the phosphor as a result of a slight change in the CaS host structure. For preparation of a CaSO4:Eu3+,Pr3+ phosphor under a H2S atmosphere, a CaS monophase was obtained. The emission and afterglow of the phosphor were similar to that prepared under the Ar-H2 (5%) atmosphere, but the afterglow time resulting from the CaS monophase was longer. The longest afterglow time obtained was about 60 min for a phosphor prepared under a H2S atmosphere with an initial Li/Ca atomic ratio of 0.04.

Preparation and properties of CdSiO3: Mn2+, Tb3+ phosphor

CdSiO3: Mn2+, Tb3+ long-lasting phosphor was prepared by the conventional high temperature solid-state method. Effects of the content of Mn2+ and Tb3+ on the luminescent properties of phosphor CdSiO3: Mn2+, Tb3+ were investigated by means of photoluminescence (PL) spectra, the afterglow intensity decay curves and the thermoluminescence (TL) spectra. It was found that when the Mn2+ and Tb3+ dopant-concentrations were 0.4mol% and 0.8mol% of Cd2+ ions in CdSiO3, respectively, the luminescence of phosphor prepared had better luminescent property and longer afterglow time. Role of Tb3+ co-doped into CdSiO3: Mn2+ matrix was discussed in this paper.

Preparation and long-afterglow luminescence research of Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu, Dy

The Ca and Ba co-doped long afterglow phosphors Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+0.01, Dy3+0.02 and only Ba doped phosphors Sr0.6Ba0.4Al2O4 ∶Eu2+0.01, Dy3+0.02 are synthesized by a high temperature solid-state reaction method. The phase structures of the phosphors are characterized by x-ray diffraction, showing that the crystal structures of samples are hexagonal. Photoluminescence spectra show that Eu2+ ion acts as the only luminescence center in sample,and Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+, Dy3+ display higher luminescent intensities due to the higher concentration of Eu2+ ions in the host crystal lattice. The decay characteristics of phosphors show that Sr0.6Ba0.2Ca0.2Al2O4 ∶Eu2+, Dy3+exhibit higher intensities in the initial afterglow process and longer afterglow time. The measurement of thermoluminescence reveals that the concentrations and depth of traps can be increased by Ca and Ba co-doping in Sr0.6Ba0.4Al2O4 ∶Eu2+, Dy3+ phosphor.

The structure and luminescence properties of long afterglow phosphor Y3−xMnxAl5−xSixO12

A series of phosphors with the composition Y3−xMnxAl5−xSixO12 (x=0, 0.025, 0.050, 0.075, 0.150, 0.225, 0.300) were prepared with solid state reactions. The X-ray powder diffraction analysis of samples shows that the substitution of Mn2+ and Si4+ does not change the garnet structure of phosphors, but makes the interplanar distance decrease to a certain extent. The emission spectra show that Mn2+ in Y3Al5O12 emits yellow–orange light in a broad band. With the increment of substitution content, the emission intensity of the phosphors increases firstly then decreases subsequently, and the emission peak moves to longer wavelength. Afterglow spectra and decay curves show that all the Mn2+ and Si4+ co-doped samples emit yellow–orange light with long afterglow after the irradiation of ultraviolet light. The longest afterglow time is 18min. Thermoluminescence measurement shows that there exist two kinds of traps with different depth of energy level and their depth decreases with the increment of substitution content.

Preparation and properties of CdSiO 3:Mn 2+, Dy 3+ phosphor

CdSiO 3:Mn 2+, Dy 3+ long-lasting phosphor was prepared by the conventional high temperature solid-state method. Effects of the content of Mn 2+ and Dy 3+ on the luminescent properties of phosphor CdSiO 3:Mn 2+, Dy 3+ were investigated by means of photoluminescence (PL) spectra and the afterglow intensity decay curves. It was found that when the Mn 2+ and Dy 3+ dopant concentrations were 1 and 0.8 mol% of Cd 2+ ions in CdSiO 3, respectively, the luminescence of phosphor prepared had better luminescent property and longer afterglow time. Role of Dy 3+ co-doped into CdSiO 3:Mn 2+ matrix was discussed in this paper.

Luminescent properties of Sr3Al2O6: Eu, Pr prepared by sol–gel method

A new red-emitting long afterglow Sr3Al2O6: Eu2+, Pr3+ phosphor was synthesized by sol–gel methods using Sr(NO3)2, Al(NO3)3·9H2O, Eu(NO3)3 and Pr(NO3)3 as raw materials. The crystalline structure of the phosphor powders were characterized by X-ray diffraction. Luminescent properties of the phosphor powders were analyzed by the fluorescence spectrophotometer. Sr3Al2O6: Eu2+, Pr3+ phosphor powders with single Sr3Al2O6 phase were prepared at 1200 °C for 2 h in the reducing atmosphere. Pr3+ doped made the light intensity and the light-lasting time of Sr3Al2O6: Eu2+, Pr3+ phosphors improved. The emission peaks of the Sr3Al2O6: Eu2+, Pr3+ phosphor powders lay at 612 nm with the excitation of 472 nm and the longest afterglow time could last for about 15 min at Pr3+ content of 0.06.

Synthesis of Long Afterglow Phosphors Doped B SrAl 2O 4:Eu 2+, Dy 3+ and Its Luminescent Properties

The long afterglow luminescent material SrAl 2O 4: Eu 2+, Dy 3+ was prepared by high temperature solid-state method. Effects of doped B on the luminescent properties of phosphors SrAl 2O 4: Eu 2+, Dy 3+ were investigated by means of excitation spectra, emission spectra and X-ray diffraction analysis. As the result, the addition of H 3BO 3 as flux promotes the growth of crystalline and reduces the synthesizing temperature, but the wavelength of emission peak of photoluminescent material did not change with the variation of H 3BO 3 content. The effect of Dy 3+ concentration on the luminescent properties of material was investigated. It was found that the luminescence of phosphors prepared under the condition of the amount of H 3BO 3 5% and the mole ratio of Eu/Dy = 1/7(Eu = 0.02 mole) had better luminescent property and longer afterglow time.

Luminescence properties of a new red long-lasting phosphor: Mg 2SiO 4:Dy 3+, Mn 2+

The red long-lasting phosphor Mg 2SiO 4:Dy 3+, Mn 2+ was prepared by solid state reaction, the luminescence and afterglow properties of which were investigated. The emission spectrum of Mg 2SiO 4:Mn 2+ shows a broad band centered at about 650 nm, which is attributed to the 4T 1( 4G) → 6A 1( 6S) transitions of Mn 2+ ions occupying two nonequivalent Mg 2+ sites. The excitation bands of 650 nm emission in near ultraviolet and visible region were assigned. Mg 2SiO 4:Mn 2+ samples co-doped with Dy 3+ show higher initial phosphorescence intensity and longer afterglow time than Mn 2+ doped ones. Both of them represent red afterglow. In addition, investigation of the effects of Dy 3+ ions in co-doped samples was conducted, indicating that Dy 3+ ions serve as trap centers.