Afterglow Properties Research Articles

Influences of Si doping on afterglow properties of Zn2Ga2.98Ge0.75-xSixO8:Cr3+0.02 nanoparicles for potential bioimaging

Zn2Ga2.98Ge0.75-xSixO4:Cr3+0.02 (ZGGSO:Cr3+) persistent luminescent nanoparticles were synthesized through a hydrothermal method along with a subsequent vacuum annealing. For these nanoparticles, it is found that NIR emissions peaked at 712 and 697 nm, originating from the 4T2-and 2E-4A2transitions of Cr3+, respectively, appear and Si4+ ions simultaneously substitute for the surface and interior Ge4+ ions. In particular, Si doping leads to the increased average particle size, the decreased crystal field strength and the tunable changes in trap depths and the energy transfer between Cr3+ and deep traps. In the case of a small amount of Si, the afterglow intensity is enhanced compared to the undoped sample due to Si doping leading to the facilitated thermal activation and tunneling processes. As the amount of dopant increases to 0.10, although the afterglow intensity is almost the same with that of the undoped sample, the dispersibility of the nanoparticles in aqueous solution is significantly enhanced. These conclusions indicate that ZGGSO:Cr3+ nanoparticles have potential in in vivo biological imaging.

Template-Modulated Afterglow of Carbon Dots in Zeolites: Room-Temperature Phosphorescence and Thermally Activated Delayed Fluorescence

Room-temperature phosphorescence (RTP) and thermally activated delayed fluorescence (TADF) materials with long afterglow lifetimes have aroused considerable interest. Here, we successfully achieve the modulation of RTP and TADF properties in a carbon dots (CDs)-in-zeolite system based on different organic templates via an in situ solvothermal synthetic method. Benefitting from the efficient stabilizing effect of triplet states of CDs by SBT zeolite matrix, CDs@SBT-1 with a larger singlet–triplet energy gap (ΔEST) of 0.36 eV exhibits predominant RTP with a lifetime of 574 ms, while CDs@SBT-2 with a smaller ΔEST value of 0.18 eV shows TADF with a lifetime of 153 ms. Further investigations reveal that different organic templates result in different CDs structures, thus modulating the ΔEST values of CDs@zeolites. This work demonstrates a facile strategy to modulate the afterglow properties of CDs@zeolite composites, which opens the possibility of designing the novel afterglow materials desired for various adv...

Excitation energy dependence for electron traps in CaTiO3:Pr, Al single crystals

We investigated the red afterglow process of CaTiO3:Pr, Al through photoluminescence and thermoluminescence measurements by using fabricated single crystals. The crystals with several cubic millimeter in size were obtained through a flux method. We found that the afterglow properties varied with the excitation energy. At room temperature, the red afterglow was observed for the charge transfer from Pr3+ to Ti4+ excitation and the direct excitation of Pr3+, while not observed for the interband excitation of CaTiO3 due to the relaxation process going through 4d15d1 state of Pr3+. For the direct excitation of Pr3+ at 80 K, the excited electrons did not reached to trap states for afterglow due to a potential barrier, which can overcome with thermal assistance at room temperature. For the charge transfer excitation at 80 K, the excited electrons could reach the traps with excess energy.

A multiwavelength analysis of a collection of short-duration GRBs observed between 2012 and 2015

AbstractWe investigate the prompt emission and the afterglow properties of short-duration gamma-ray burst (sGRB) 130603B and another eight sGRB events during 2012–2015, observed by several multiwavelength facilities including the Gran Canarias Telescope 10.4 m telescope. Prompt emission high energy data of the events were obtained by INTEGRAL-SPI-ACS, Swift-BAT, and Fermi-GBM satellites. The prompt emission data by INTEGRAL in the energy range of 0.1–10 MeV for sGRB 130603B, sGRB 140606A, sGRB 140930B, sGRB 141212A, and sGRB 151228A do not show any signature of the extended emission or precursor activity and their spectral and temporal properties are similar to those seen in case of other short bursts. For sGRB 130603B, our new afterglow photometric data constrain the pre-jet-break temporal decay due to denser temporal coverage. For sGRB 130603B, the afterglow light curve, containing both our new and previously published photometric data is broadly consistent with the ISM afterglow model. Modeling of the host galaxies of sGRB 130603B and sGRB 141212A using the LePHARE software supports a scenario in which the environment of the burst is undergoing moderate star formation activity. From the inclusion of our late-time data for eight other sGRBs we are able to: place tight constraints on the non-detection of the afterglow, host galaxy, or any underlying ‘kilonova’ emission. Our late-time afterglow observations of the sGRB 170817A/GW170817 are also discussed and compared with the sub-set of sGRBs.

Scintillation properties of Ce- and Eu-doped Ca2MgSi2O7 crystals

Ce- and Eu-doped Ca2MgSi2O7 (CMSM) single crystals were synthesized by the Floating Zone method. From the X-ray diffraction patterns, we confirmed that all the CMSM samples have no impurity phases. Under X-ray irradiation, the Ce- and Eu-doped CMSM samples showed scintillation with a broad emission around 390 nm and 530 nm, respectively. The origin of these emissions was considered to be the 5d-4f transitions of Ce3+ and Eu2+, respectively. The absolute light yield of the Eu-doped CMSM sample was 11,000 ph/MeV evaluated under 241Am γ-ray (59.5 keV). In addition, afterglow properties of the Ce- and Eu-doped samples were consistent with the corresponding thermoluminescence properties.

Achieving Dual‐Emissive and Time‐Dependent Evolutive Organic Afterglow by Bridging Molecules with Weak Intermolecular Hydrogen Bonding

AbstractIt is discovered that “bridging” traditional persistent room‐temperature phosphorescence (pRTP) dibenzofuran moieties by intermolecular hydrogen bonding can induce interesting photophysical properties. The light‐emitting material 4‐(4‐((4‐methoxyphenyl)sulfonyl)phenyl)dibenzo[b,d]furan (SOBF‐OMe) is synthesized and excitingly shows novel dual‐emissive afterglow material properties in which orange pRTP (at ≈580 nm, 627 ms) from the dibenzofuran moiety and another blue ultralong intermolecular charge transfer emission (≈476 nm, 204 ms, with TADF characteristics) can be detected. Due to the different decay lifetimes, the ratio of the two afterglow emission bands continuously changes. Accordingly, the emission colors are unusually tuned gradually from cold‐white to orange during the afterglow decay process. The blue afterglow emission, which relates to intermolecular interactions, is sensitive to mechanical stimuli and the afterglow emission properties of SOBF‐OMe (single‐emissive or dual‐emissive) can easily be manipulated by grinding/fuming. This single‐component material is a rare example of a light‐emitting compound showing dual‐emissive and real‐time changing afterglow properties in which a rational bridging strategy via weak intermolecular hydrogen bonding is utilized.

Insights into the element gradient in the grain and luminescence mechanism of the long afterglow material Sr2MgSi2O7: Eu2+,Dy3+

In the long afterglow luminescent material, the defects play an important role on the afterglow performance, but the understanding of the traps are still not uniform. In this research, the long afterglow material Sr2MgSi2O7: Eu2+, Dy3+ is treated by the acid corrosion liquid with different times to research gradient distribution of elements from outside to inside the grain of the long afterglow materials, the effect of the gradient on the structure, photoluminescence performance, long afterglow properties as well as the mechanism of luminescence are discussed. When the grain surface is destroyed, the initial brightness falls sharply, but the decrease of decay times are not obvious, that is caused by the different distribution of defects. The amounts of element Sr and O increase, but the Eu and Dy decrease from the outside to the inside the grain, the aggregate defects (VO··VSr′′EuSr)n or (2DySr·VSr′′ EuSr)n which act as shallow traps are proposed, and meanwhile the isolated defects VO··, DySr· and VSr′′ act as deep traps. A new luminescent model is put forward to account for the long afterglow photoluminescence phenomenon, the shallow traps and the deep traps play different roles on the long afterglow properties, and most of the problems that exist in the long afterglow materials can be explained by this model.

Structural characterization and luminescence properties of Dy3+ doped Ca3MgSi2O8 phosphors

Different concentrations of Dy3+ doped Ca3MgSi2O8 phosphors were synthesis by solid state reaction method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermoluminescence (TL) and photoluminescence (PL) were carried out. The absorption band located at 351 nm is a main excitation peak matching with the emission of near white light emitting diodes ultraviolet light (400–700 nm). The emission spectra consist mainly group of three emission bands, which are situated around 482 nm, 493 nm (both correspond to blue emission) and 574 nm (correspond to yellow emission). These bands can be assigned to the transitions 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. The concentration quenching effect for Dy3+ was found at the optimum doping concentration of 2.0 mol %. The thermoluminescence results show that the corresponding increase or decrease in afterglow is associated with trap density, but no change in trap depth. The underlying reason of photoluminescence and afterglow property is discussed. The prepared phosphor may be useful for eco-friendly lighting technology.

Nanothick aluminate long-afterglow phosphors using inherited hydrothermal deriving

A novel strategy of the inherited hydrothermal method was used to prepare SrAl2O4: 0.01Eu2+, 0.01Dy3+ (SAO) without boron (ISAO) and boron-doping (BSAO) via NaAlO2 as an aluminum source and mineralizer at 200 °C for 6–24 h. The investigated optical properties was correlated to phase transformation and phosphor morphology. The main constituting phases of Al2(OOH)2 and SrCO3 transformed to monoclinic SrAl4O7 and mixed monoclinic/hexagonal SrAl2O4 then pure monoclinic SrAl2O4 during different hydrothermal period. The hydrothermally prepared samples exhibited flower-like morphology. The annealed plate phosphors with nanothick single crystals inherited from hydrothermal feature. The shift of photoluminescence (PL) peak wavelength corresponded to the phase transformation from SrAl4O7 to SrAl2O4 with hydrothermal time for ISAO and BSAO. The PL intensity increased with hydrothermal time due to achieving the pure SrAl2O4 phase with preferred orientation geometry and further enhanced by boron-doping. The afterglow of BSAO was significantly enhanced than ISAO, solid-state prepared MSAO and commercial SAO at the initial 100 s after excitation cut-off. The boron doped in the BSAO was scarcely on the grain surface as to small grain size. Thus, the afterglow enhancement should be attributed to the boron in the lattice inducing defect traps. Overall, the inherited hydrothermal and boron-doping derived nanothick SAOs with large surface preferred orientation enhanced the PL and afterglow properties.

A new yellow long persistent luminescence phosphor Ca2Al2SiO7:Eu2+,Tm3+ found by co-doping Ln3+ (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) with Eu2+ in Ca2Al2SiO7 host

A series of Eu2+ doped Ca2Al2SiO7 (CASO) phosphors with or without Ln3+ (Ln = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) co-dopant in the host were synthesized by solid-state reaction method in order to obtain long persistent luminescence (LPL). Their structural and photoluminescent properties were investigated by X-ray powder diffraction (XRD) and photoluminescence emission (PL) and excitation (PLE) spectra in detail. Meanwhile, the decay curve measurements were performed on those phosphors to study their afterglow properties. Among them, the Ca2Al2SiO7:Eu2+,Tm3+ (CASO:Eu,Tm) phosphor yielded a bright LPL in the yellow region with afterglow duration much longer than those of other samples. Its luminescence can be observed by human eye for more than 2 h after shutting down the 365 nm excitation source. Further thermoluminescence (TL) study on CASO:Eu,Tm phosphor indicated that the introduced Tm3+ ions indeed increased substantially the amount of charge carrier traps. A possible explanation were given to illustrate the LPL mechanism of CASO:Eu,Tm based on the experimental results. This work suggests that CASO:Eu,Tm phosphor is a promising yellow-emitting LPL phosphor.

LRET-based functional persistent luminescence nanoprobe for imaging and detection of cyanide ion

Cyanide anion is an inhibitor of the enzyme cytochrome c oxidase in the fourth complex of the electron transport chain, and usually found in the membrane of the mitochondria of eukaryotic cells, thus exploration of novel analytical methodology for sensitive and accurate detection of cyanide ion in cells is vital and urgent. Herein, we successfully prepared and surface-modified ZnGa2O4:Mn2+ PLNPs with excellent afterglow properties, small size and preferable dispersibility. Furthermore, we report a rational design and fabrication of a functional PL nanoprobe based on luminescence resonance energy transfer (LRET), which for the first time demonstrates detection of cyanide ion without external illumination. The nanoprobe is composed of two main moieties: PLNPs with excellent afterglow properties as energy donor; and DEHSPI, a chromophore with tunable light absorption, as both energy acceptor and CN− recognition element. PL can be effectively quenched by the chromophores assembled on the surface of PLNPs through a LRET process and subsequently recovered upon the addition of CN−. Importantly, the persistent afterglow nature highlights the merits of employing PLNPs as energy donor to eliminate the background noise under in situ excitation. Moreover, the nanoprobe exhibits excellent analytical properties and low cytotoxicity for bio-imaging of CN− in living cells.

Three-dimensional printing of hybrid organic/inorganic composites with long persistence luminescence

Additive manufacturing (AM) techniques allow for the construction of sophisticated and hollow models based on the needs of customers, and they functionalize the raw materials (e.g., metal, polymer and ceramic) by structuring them. Here, we demonstrate a simple method for the realization of a three-dimensional architecture with long afterglow properties by curing organic resin doped with inorganic long persistent phosphors (LPPs) layer by layer through the stereolithography (SLA) technique. In our process, the LPPs made by solid state reaction were incorporated homogenously into a resin matrix and pre-designed 3D structures with the resolution of 0.1 mm were printed out. The high luminescence, considerable decay time and multi-color make these organic/inorganic composites reliable for applications in artifacts, crafts, toys and night indicators. It is also demonstrated that the resin containing SrAl2O4: Eu2+, Dy3+ phosphors can be used for fiber temperature sensing from 40 °C to 70 °C.

Effect of Co-Dopant on the Phase Structure and Photoluminescence Properties of Sr2mgsi2O7: En2+ Phosphors

The role of co-dopants, i.e. Dy, Ce, Tb or Y in SMS : Eu, RE3+ phosphor sintered using solid state reaction method at 1250°C under forming gas was studied. All SMS phosphors exhibited tetragonal Sr2MgSi2O7 as the domain phase and monoclinic SrSiO3 as the minor phase based on XRD analysis. It is noted that only single blue emission (469nm) contributed by Eu2+ ions was detected in RTPL measurement regardless types of co-dopants introduced during the sintering process. This result indicates that the co-dopants did not act as luminance centres in the SMS phosphor. The time-decay PL and temperature dependent PL analysis suggest that Ce3+ ions acted as sensitizer which improved the luminescence intensity and afterglow property of SMS phosphor. The present of Dy3+ ions pro-longed the afterglow property by introducing more traps density in the SMS phosphor structure. The co-doping of Tb or Y into the SMS phosphor generated many non-radiative recombination centres which deteriorated the optical performance of SMS: Eu2+, RE3+ phosphor.

Crystallization and Optical Properties of Sr<sub>3</sub>Al<sub>2</sub>O<sub>6</sub>-SrAl<sub>2</sub>O<sub>4</sub> Eutectic Glass

SrO-Al2O3 ceramics has prospective applications due to its photo-luminescence and persistent afterglow properties. Sr3Al2O6-SrAl2O4 eutectic glass was prepared by using the aerodynamic levitator equipped with a CO2 laser device. The prepared Sr3Al2O6-SrAl2O4 eutectic glass beads were further heat-treated at temperature from 880°C to 980°C. The phase evolution, crystallization behavior, optical transmittance and mechanical properties of the annealed eutectic glass ceramics were investigated. The as-prepared glass is colorless and transparent over a wide range from ultraviolet to near-infrared region, and the average in-line transmittance is over 80% in the range of 260-3200nm. There were two crystal phases Sr3Al2O6 and SrAl2O4 crystallized from the glass beads. With increasing heat-treatment temperature, the transparency of the samples decreased, and the hardness increased. The prepared Sr3Al2O6-SrAl2O4 eutectic glass and glass ceramics may be a promising candidate for the development of photo-luminescence and persistent afterglow materials.

Enhanced performance of Sr2Si5N8: Eu2+ red afterglow phosphor by co-doping with boron and oxygen

Herein we report the improvement in persistent luminescence of Eu2+ doped Sr2Si5N8 nitride phosphor. A systematic experiment has been performed to investigate the influence of co-doping B3+, O2-, Tm3+ in Sr2Si5N8: Eu2+. It is found that B3+ and O2- co-doped Sr2Si5N8: Eu2+ phosphor exhibits better afterglow properties with higher afterglow intensity, which can be attributed to larger trap density. The afterglow luminescence mechanism in Sr2Si5N8: Eu2+, B3+, O2- is discussed on the basis of the host referred binding energy (HRBE) scheme of Sr2Si5N8, the relative energy level positions of 5d and 4 f electron of Eu2+ and the trap depth in the host lattice.

Ba1.3Ca0.7SiO4:Eu2+, Mn2+: A white-lighting-emitting phosphor with extra afterglow properties via YF3 addition

Here, Ba1.3Ca0.7SiO4:Eu2+, Mn2+ phosphor was found to exhibit an afterglow property after doping Y3+ ions. The phosphors were synthesized by a precipitation method using NH4Cl as the flux agent. X-ray diffraction, photoluminescence, afterglow phosphorescence, and thermoluminescence spectra were used to characterize the structures and properties of the prepared phosphors. After irradiation under UV light at 365 nm, these phosphors emitted white light that can be seen clearly by the naked eye in the darkroom. The light can still be seen even after the excitation source was removed for 30 s. In addition, the depth of the traps was investigated. The exhibited white light afterglow luminescence is a valuable in application of alternating current (AC) UV-irradiated WLED, because it can compensate for the strobe flash problem caused by AC.

A surface corrosion and expansion mechanism on thermal degradation of SrAl2O4:Eu2+, Dy3+

The thermal degradation of SrAl2O4:Eu2+, Dy3+ phosphor limits its application in high temperature products. To clarify its thermal degradation mechanism, a heat-treatment process was carried out, and the interrelation of luminescent degradation, surface chemical composition and heat-treatment temperature was investigated. The results revealed that the afterglow properties degraded obviously with the increasing heat-treatment temperature, while the instantaneous emission intensity appeared two maximum values. According to the luminescent mechanism of long afterglow materials and the results of thermoluminescence spectra, two maximum values corresponded to the destruction of two trap levels at different temperatures. X-ray photoelectron spectroscopy results showed that the element composition of Sr and O on the phosphor surface increased with the increasing heat-treatment temperature, confirming that a SrO layer formed on the surface. Based on above results, we proposed a surface corrosion and expansion mechanism on the thermal degradation of SrAl2O4:Eu2+, Dy3+.

A facile method to prepare the white persistent luminescent fibers based on Sr2ZnSi2O7Eu2+, Dy3+ and fluorescence pigments

The polyacrylonitrile composite fibers with white persistent luminescence were prepared by adding different concentrations of Sr2ZnSi2O7: Eu2+, Dy3+ (SZO) and Rhodamine B fluorescent pigments (FP) into polyacrylonitrile spinning solution. Morphology, phase structure, color properties, photoluminescence properties and afterglow properties were examined. Photoluminescence test indicated that the emission spectrum of Sr2ZnSi2O7: Eu2+, Dy3+ phosphors overlapped with the excitation spectrum of fluorescent pigments in the range of 450–550 nm, which was the necessary condition for the energy transfer from the Sr2ZnSi2O7: Eu2+, Dy3+ to the Rhodamine B fluorescent pigments (FP). The phosphorescent color of the composite fibers showed that the white luminescent polyacrylonitrile fibers can be gained when weight ratios of SZO/FP ranged from 10:0.2 to 10:0.5. Decay curves suggested that the as weight ratio of SZO/FP was less than 10:0.75, the initial brightness of the composite fibers could not be significantly reduced.

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.

Comparison of the luminescent properties of warm-toned long-lasting phosphorescent composites: SiO2/red-emitting color converter@SrAl2O4:Eu2+, Dy3+ and PMMA/red-emitting color converter@SrAl2O4:Eu2+, Dy3+

Two kinds of warm-toned (yellow/orange-emitting) long-lasting phosphorescent composites, namely, SiO2/red-emitting color converter@SrAl2O4:Eu2+, Dy3+ (SiO2/RECC@SAOED) and PMMA/red-emitting color converter@SrAl2O4:Eu2+, Dy3+ (PMMA/RECC@SAOED), were prepared in this study. Their morphological and luminescent properties were compared with those of the uncoated SAOED phosphor and analyzed in detail. SiO2/RECC@SAOED and PMMA/RECC@SAOED particles presented a coarse surface with an increased diameter of 12 µm. In addition to the first emission peak at 525 nm similar to that of the uncoated SAOED, an emission peak occurred in the emission spectra of SiO2/RECC@SAOED and PMMA/RECC@SAOED at 610 and 612 nm, respectively. The chromaticity coordinates of SiO2/RECC@SAOED and PMMA/RECC@SAOED moved to the yellow (x = 0.3769, y = 0.5006) and orange (x = 0.4647, y = 0.4671) areas compared with those of the uncoated SAOED in the green area (x = 0.2781, y = 0.5777). The afterglow decay curve revealed that the afterglow property of SiO2/RECC@SAOED was better than that of PMMA/RECC@SAOED.