Long Afterglow Research Articles

Long afterglow (LAG) photoluminescence effect in ce-doped optical fiber

Ce-doped optical fibers were irradiated with various light sources, which are purple, blue, green, and red LEDs, for 30 minutes to investigate their long-after glow (LAG) characteristics. Photons were counted with a photo-multipliers tube (PMT) for 30 min, depending on the time immediately after irradiation. Depending on the wavelength of the LED, the maximum count was obtained as a result of excitation with a purple LED. The glow time was found to be about 90 minutes. The photon counting was performed for 30 minutes to characterize the irradiation time effect, depending on the irradiation time (2, 5, 10, and 30 minutes) with the purple LED. Consequently, the glow intensity and duration increased due to increased irradiation time. Additionally, the Ce-doped optical fibers were irradiated with a fluorescent lamp for 30 and 60 minutes and direct sunlight for 30 minutes. All results were fitted by a function that obtained decay time parameters. The decay times increase as the better LAG characteristics and the results confirm the decay times increase.

Albumin assisted sol-gel synthesized SrSnO3: Pr3+ red persistent phosphors for temperature sensing

SrSnO3: Pr3+ phosphors with red long afterglow (LAG)and temperature sensing were prepared by albumin assisted sol-gel method. The typical sample had cubic structure. The mean particle size was about 2.02 μm. The band gap values of samples were in the range of about 4.06–4.09 eV. The luminescent properties and LAG behaviors of SrSnO3: Pr3+ phosphors were investigated and the luminescence mechanism of red LAG was discussed. Albumin assisted SrSnO3: Pr3+ phosphor with a red long afterglow had an average decay time of 74.25 s. Pr3+ ions not only act as an activator, emitting red long afterglow, but also act as a trap provider. Moreover, the temperature sensing property was studied based on the non-thermal coupling FIR of TE and 3P0→3H4 transition emission. The relative sensitivity was as high as 3580.89/T2. The absolute sensitivity (Sa) and relative sensitivity (Sr) of SrSnO3: 0.5%Pr3+ were 0.0374 K-1 and 4.03% K−1, respectively. Its optical thermometry performance is better than that of most phosphors. It has the potential to be applied in the field of temperature sensing.

Long afterglow properties of the blue emission from Pr3+-activated Sr5Ta4O15 phosphor

In this study, a novel blue emitting long afterglow (LAG) material based on Pr3+-doped Sr5Ta4O15 was prepared successfully using a conventional solid-state reaction method. The photoluminescence spectra, excited-state decay curve, LAG decay curve, and thermoluminescence glow curve were obtained to investigate the properities of Sr5Ta4O15:Pr3+ systematically. The blue LAG emission from Pr3+ was observed after excitation with a 254-nm ultraviolet lamp. The optimal doping concentration of Pr3+ for the best LAG performance was experimentally determined to be approximately 4 mol%. Based on the experimental results, a possible model was constructed to illustrate the mechanism of LAG in detail.

Cr3+‐activated Li5Zn8Al5Ge9O36: A near‐infrared long‐afterglow phosphor

AbstractNear‐infrared long‐afterglow (LAG) materials have attracted considerable attention owing to their high potential for in vivo imaging applications. Here, we present a series of near‐infrared LAG phosphors Li5Zn8Al5−xGe9O36:xCr3+ (LZAG:Cr3+), which were synthesized using a solid‐state reaction method. The pure LZAG host exhibits blue photoluminescence and LAG emission. We investigated the effect of the zinc vacancy contents on the photoluminescence and LAG performance by adjusting the zinc content and introducing Ga3+ ions to substitute the Zn2+ sites in LZAG host. When Cr3+ ions were introduced into the LZAG host, LZAG:Cr3+ produced a strong, broad blue emission band centered at 456 nm and a near‐infrared emission band at 700 nm caused by the 2E → 4A2 transition of Cr3+. The energy transfer processes from the LZAG host to Cr3+ were identified in the photoluminescence and LAG process. After irradiation at 258 nm for 10 minutes, the LAG emission of LZAG:0.008Cr3+ can last nearly 2.5 hours. Moreover, the LAG intensity and duration of LZAG: 0.008Cr3+ were significantly improved by introducing a small dose of Ga3+ ions. Finally, the traps and mechanism of LAG in LZAG, LZAG:Ga3+, and LZAG:Cr3+ were discussed in detail.

Reversible white-brown photochromism in a self-activated long-persistent phosphor Mg_2SnO_4

Recently, considerable attention has been paid to photochromic (PC) materials owing to its great potential application in various fields, such as rewritable copy papers, erasable optical memory media, smartwindows, sensors, photoswitches and so on. Up until now, most of PC materials come from organics. However, we report that a self-activated LAG phosphor possesses PC property based on non-doped Mg2SnO4 synthesized via a traditional solid-state reaction method. The photoluminescence and long afterglow (LAG) properties were investigated. Interestingly, the white surface color can be colored into brown by ultraviolet-light (UV) irradiation. After visible light irradiation or heat-treatment, the colored Mg2SnO4 can be bleached into white again. The reversible white-brown PC properties of Mg2SnO4 were characterized by diffuse reflectance spectra. Based on the observed phenomena and the obtained experimental results, a tentative model was constructed to illustrate the LAG and PC mechanism.

Synthesis and luminescence of Sr2Ta2O7:Pr3+: a novel blue emission, long persistent phosphor

Abstract

Photoluminescence and long persistent luminescence properties of a novel green emitting phosphor Ca3TaAl3Si2O14:Tb3+

A Tb3+ doped Ca3TaAl3Si2O14 phosphor has been prepared successfully through a conventional solid-state reaction method. X-ray diffraction patterns indicate that the Tb3+ doping does not show obvious effect to the crystal structure of Ca3TaAl3Si2O14 (CTAS) host lattice. The luminescent properties were studied systematically by measuring photoluminescence spectra, decay curves, afterglow spectra and thermo-luminescence glow curves. The pure CTAS host with strong absorption in the range of 250–400 nm and could give a blue emission centered at about 493 nm. When Tb3+ ions were doped, the blue long afterglow (LAG) emission from Tb3+ was observed after stimulated by 254 nm ultraviolet lamp. The optimal doping concentration of Tb3+ for LAG performance was experimentally to be approximately 0.5 mol%. Based on the experimental results, a model was constructed and the relevant mechanism of afterglow was illustrated in detail.

Luminescence properties of a novel greenish-blue emission long persistent phosphor Sr3TaAl3Si2O14:Pr3+

Pr3+exhibits prominent red emission in most oxide phosphors, which derives from the 1D2→3H4 transition, and green or blue emission from 3P0→3H4, 5 transitions are normally less intense in most cases. However, a greenish-blue emission was observed from Sr3TaAl3Si2O14:Pr3+prepared via solid state reaction. All as-prepared phosphors were studied systematically by X-ray diffraction (XRD), photoluminescence spectra, decay curves, long afterglow (LAG) spectra and thermoluminescence (TL) glow curves. Based on the excitation and emission spectra, the Sr3TaAl3Si2O14 (STAS) host is proved to be a self-activated luminescent host lattice. In the emission spectra for Pr3+doped STAS, the predominant greenish-blue emission locating at ~489nm and ~507nm coming from 3P0,1→3H4 transitions were observed. And the different mechanisms for concentration quenching in both cases were discussed. At last, a model was proposed on the basis of experimental results to discuss the LAG mechanism of STAS:Pr3+in detail.

Crystal phases, photoluminescence, and long-afterglow luminescence of SrAl2O4: Eu2+, Dy3+ - xB2O3 (0 ≤ x ≤ 0.4) phosphors

SrAl2O4: 0.04Eu2+, 0.08Dy3+ - xB2O3 (0 ≤ x ≤ 0.4) phosphors were synthesized by using the conventional solid-state reaction route. The long-afterglow (LAG) luminescence increased notably up to x = 0.3, followed by a slight decrease at x = 0.4. A good correlation between the LAG luminescence and the total quantity of the luminescent crystalline phases (SrAl2O4 and Sr4Al14O25) was found, based on the Rietveld refinement of the X-ray diffraction pattern. However, through a comparison of the PL excitation/emission with the LAG luminescence, we concluded that the maximal LAG luminescence was not only governed by the quantity of the luminescent host but also by the quality of the host (the concentration of the doped Eu2+ and especially the Dy3+ in the luminescent phases).

CaTiO3:Eu3+, a potential red long lasting phosphor: Energy migration and characterization of trap level distribution

This paper comprises a promising approach for the development of a red-light emitting CaTiO3:Eu3+ long-lasting phosphor. Eu3+ doped CaTiO3 phosphors were prepared by the solid state reaction method at 1000°C. Red long-afterglow (LAG) originated from the f–f transitions of Eu3+ in the CaTiO3 and lasted for several minutes. Defect trap depth values from 0.62 up to 1.21eV were obtained from thermoluminescence (TL) data. These defects were created due to charge compensation. These traps were responsible for the afterglow emission at room temperature. The decay curves and TL glow curves showed that the density of the traps with suitable depth has been significantly changed with an increase in dopant concentration. The depth and density of the traps can affect the LAG performance. The possible mechanism behind the LAG of Eu3+ in CaTiO3 was explained in detail on the basis of the trap distribution.

Luminescent properties of a reddish orange emitting long-lasting phosphor CaO:Pr3+

Abstract A novel reddish orange emitting long persistent phosphor CaO:Pr was prepared by a high temperature solid-state reaction method. All as-prepared phosphors were studied systematically by X-ray diffraction, photoluminescence (PL) spectra, decay curves, afterglow spectra and thermoluminescence (TL) glow curves. The intensity of PL and the performance of afterglow are dependent on the concentration of Pr3+ ions. The trap depth in the range between 0.5 and 0.7 eV is suitable for long afterglow (LAG). The optimal concentrations of Pr3+ ions for the best characteristic PL emission and afterglow were experimentally calculated to be 0.05 mol%. After irradiation by 273 nm for 3 min, the duration of reddish orange afterglow can last nearly 1 h. The decay processes and mechanism of LAG in CaO:Pr3+ were also discussed in detail.

Solid state synthesis of SrAl2O4:Mn2+ co-doped with Nd3+ phosphor and its optical properties

The optical properties of alkaline earth aluminates doped with rare earth ions have received much attention in the last years and this is due to their chemical stability, long-afterglow (LAG) phosphorescence and high quantum efficiency. However, there is a lack of understanding about the nature of the rare earth ion trapping sites and the mechanisms which could activate and improve the emission centers in these materials. Therefore a new phosphor material composition, SrAl2O4:Mn2+, co-doped with Nd3+ was synthesized by a traditional solid-state reaction method. The influence of transition metal and rare earth doping on crystal structure and its luminescence properties have been investigated by using X-ray diffraction (XRD), Raman scattering, Photoluminescence (PL) and Radioluminescence (RL). Analysis of the related diffraction patterns has revealed a major phase characteristic of the monoclinic SrAl2O4 compound. Small amounts of the dopants MnCO3 and Nd2O3 have almost no effect on the crsytalline phase composition. Characteristic absorption bands from Nd3+ 4f–4f transitions in the spectra can be assigned to the transitions from the ground state 4I9/2 to the excited states. The luminescence of Mn2+ activated SrAl2O4 exhibits a broad green emission band from the synthesized phosphor particles under different excitation sources. This corresponds to the spin-forbidden transition of the d-orbital electron associated with the Mn2+ ion. In photo- and radio-luminescence spectra, Nd3+ 4f–4f transition peaks were observed. The emitted radiations for different luminescence techniques were dominated by 560, 870, 1057 and 1335nm peaks in the visible and NIR regions as a result of 4I9/2→4G7/2 and 4F3/2→4IJ (J=9/2, 11/2 and 13/2) transitions of Nd3+ ions, respectively. Multiple emission lines observed at each of these techniques are due to the crystal field splitting of the ground state of the emitting ions. The nature of the emission lines is discussed.

Luminescent properties of a red afterglow phosphor Ca2SnO4:Pr3+

A novel red light emission long persistent phosphor, Ca2SnO4:Pr3+, was prepared by a high temperature solid-state reaction method. All as-prepared phosphors were studied systematically by X-ray diffraction, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence (TL) glow curves. Four main emission peaks of afterglow spectrum locate at 496, 605, 625 and 658nm corresponding to CIE chromaticity coordinates of x=0.506, y=0.355. The intensities of photoluminescence and the performance of afterglow are dependent on the concentration of Pr3+ ions. The traps with depth of 0.79–0.82eV are the origination of long afterglow (LAG). The optimal concentration of Pr3+ ions for the best afterglow characteristic was experimentally to be 0.3mol%. After irradiation by 254nm, the duration of red afterglow can last about 20min. The mechanism of LAG in Ca2SnO4:Pr3+ was also discussed in detail.

Persistent luminescence in Bi3+ doped CaWO4 matrix

A series of persistent phosphors CaWO4:Bi3+ were prepared via a traditional solid state method at 1000 °C in air atmosphere. The photoluminescence (PL) and long afterglow (LAG) properties were investigated systematically. The optimal Bi3+ ions concentration was experimentally determined to be 0.15 mol% and the performance of afterglow was greatly improved with the incorporation of equivalent amount of Li+ ions. Both WO42− and Bi3+ ions can act as luminescent centers. The emission of blue long afterglow is observed. The origin of this phenomenon is confirmed to the transition from 3P1 to 1S0 in Bi3+ ions. Defects BiCa· serve as electron traps and Ca2+ vacancies mainly act as new hole trapping centers. In order to study the trapping process and explain the mechanism of long afterglow, a schematic model is also proposed and discussed in detail.

Luminescence properties of a novel orange emission long persistent phosphor CaO:Sm3+

A novel Sm3+-doped CaO phosphor was synthesized by a traditional high temperature solid-state reaction method. The luminescence properties were studied and orange long afterglow was observed for the first time. The dependence of photoluminescence (PL) and long afterglow (LAG) properties on Sm3+ contents were investigated systematically. The optimal concentrations of Sm3+ ions for the best PL and LAG properties were experimentally to be 0.4 and 0.3mol%, respectively. After irradiation by 254nm for 3min, the duration of orange afterglow can last nearly 40min. The traps caused by the incorporation of Sm3+ ions are responsible for the generation of orange LAG. The mechanism of LAG was also illustrated briefly.

Effect of nominal substitution of Dy3+ for host cations in SrAl2O4: Eu2+ phosphor on phase evolution and long afterglow luminescence

SrAl2O4: Eu2+, Dy3+ long-afterglow (LAG) phosphors with nominal substitution of Dy for Al site demonstrated superior performance as compared to the cases of nominal substitution for the Sr site or excess addition, despite the fact that a reduced quantity of the SrAl2O4 main host phase existed when Dy3+ was nominally substituted for Al. It was deduced that if the number of Al available for the formation of the main host was less than the stoichiometric value of 2 with reference to the number of Sr lattice site in the main host, boron would suitably join the [Al,B]O4 structural unit, yielding an improved incorporation of Dy3+ to the SrAl2O4 main host which, in turn, improves the LAG luminescence.

Combustion synthesis of Sr 3MgSi 2O 8:Eu 2+ and Sr 2MgSi 2O 7:Eu 2+ phosphors

Sr 3MgSi 2O 8:Eu 2+ and Sr 2MgSi 2O 7:Eu 2+ phosphors find uses in applications such as plasma display panel (PDP), solid-state lighting, longafter glow. Preparation of these phosphors by a modified combustion synthesis is described in this paper. As-prepared samples did not show photoluminescence. After reducing the samples at 900 °C, characteristic Eu 2+ emission was observed. Preparation of these phosphors by using similar methods helped clarifying various results obtained for Sr 3MgSi 2O 8:Eu 2+ by different investigators.