Afterglow Decay Curves Research Articles

The decay curves of luminescence from Eu2+ in β-SiAlON are effectively analyzed using the general-order kinetics formula

Defects in phosphors affect not only luminescence intensity but also emission peak width, decay time, and afterglow. The green phosphor β-SiAlON:Eu2+ exhibits the green emission of Eu2+ at 520 nm and the blue emission of nitrogen vacancies at 460 nm in time-resolved fluorescence measurements. The decay time of the intrinsic Eu2+ transition is 0.7 μs, but afterglow is detected from 50 μs to 0.01 s. This afterglow decay curve is the same for the green emission of Eu2+ and the blue emission of nitrogen vacancies, suggesting that the defect levels of the nitrogen vacancies affect the Eu2+ transition. The afterglow decay curves were analyzed using the formula of the general-order kinetics, 1+t/τB−n , where n is the decay power and τB is the decay time. This equation is generally used when analyzing afterglow on the order of seconds to hours but has not been examined systematically applied in samples with different concentrations of Eu2+ and temperatures on the order of nanoseconds to milliseconds. The decay power n is approximately 1 for all Eu2+ concentrations (x = 0.001–0.3) and undoped β-SiAlON. The decay time τB is correlated with the density of the nitrogen vacancies determined by electron spin resonance. Furthermore, the value of n is approximately 1 for 50 μs to 0.01 s and 0.3 for 1–1000 s. Thus, the luminescence mechanism of Eu2+ can be discussed by comparing n and τB obtained from the decay curves. In addition, several different Eu2+-doped phosphors, namely SrAl2O4:Eu2+, Dy3+, CaAlSiN3:Eu2+, and CaS:Eu2+, Tm3+, are studied.

A new insight into the mechanism of persistent luminescence phosphors SrS: Eu2+, Pr3+

The red persistent luminescence phosphors SrS: , (x = 0∼0.001, y = 0∼0.003) were synthesized by the solid-state reaction method in a weak reducing atmosphere of active carbon. The synthetic parameters, photoluminescence characteristics, and dynamic properties of thermoluminescence of the phosphors were studied systematically. According to the results of photoluminescence spectra of SrS: , , the energy level scheme of the phosphors was confirmed quantitatively. Based on the studies of the scanning electron microscope (SEM), UV-Visible absorbance spectra, afterglow decay curves, thermoluminescence(TL) spectra, and X-ray photoelectron spectroscopy (XPS) spectra, we found that the SrS: , (SSEP) phosphor presented the best persistent luminescence property, which mainly resulted from its outstanding absorbance characteristic, deeper depth of () defects, and fewer defect concentration belonging to the higher-order kinetics. Those comprehensive results deduced that a complex defect ()- should present in the Eu2+ doping phosphors, and the Pr3+ doping will produce defects, which can suppress the formation of () defects and increase their energy depth.

Synthesis of a CaAl2O4:Eu2+, Dy3+ Phosphor by the Polymer Slurry Method and Its Application in Anticounterfeiting

CaAl2O4:Eu2+, Dy3+ long-afterglow-luminescence materials were prepared by a high-temperature solid-state reaction assisted by the polymer slurry method (HTSSR-PS). X-ray diffraction and scanning electron microscopy were employed to observe the crystal structure and microstructure of CaAl2O4:Eu2+, Dy3+ phosphors. In addition, density functional theory calculations were utilized to investigate the electronic and crystal structures of CaAl2O4. Fluorescence spectra and afterglow decay curves characterized luminescence properties. Thermoluminescence curves characterized the optical storage performance. CaAl2O4:Eu2+, Dy3+ sintered at 1300 °C exhibited the highest crystallinity and the best afterglow performance. Compared to the conventional HTSSR method, the calcination temperature was significantly lower, and the performance was improved. The method was simple, with lower energy consumption, and it was more suitable for large-scale production. In addition, the application of CaAl2O4:Eu2+, Dy3+ in dynamic anticounterfeiting was demonstrated by exploiting a unique afterglow property.

Luminescent properties of Mg1.99SnO4:0.01Mn2+ phosphors doped with Zn2+

In this work, a series of ZnxMg1.99-xSnO4:0.01Mn2+ (x = 0, 0.01, 0.02, 0.03, 0.04) green long afterglow phosphors are prepared by high-temperature solid-phase reaction. The photoluminescence and long afterglow performance of host material doped with Zn2+ are investigated. The results show that the emission peak of Mn2+ is red-shifted by 5 nm with increasing Zn2+ concentration. Zn0.03Mg1.96SnO4:0.01Mn2+ phosphor has the strongest green luminescence intensity with the chromaticity coordinates of (0.085 7, 0.608 3) under 270 nm, and Zn0.01Mg1.98SnO4:0.01Mn2+ phosphor has superior long afterglow performance with average lifetime of 102.41s. The afterglow decay and thermoluminescence curve of phosphor are used to explain the mechanism of long afterglow luminescence. Meanwhile, the afterglow intensity distribution of each pixel in Zn0.01Mg1.98SnO4:0.01Mn2+ coating samples is carried out by hyperspectral imaging, and the optimal luminescence intensity and uniformity of the sample are obtained at a phosphor/epoxy mass ratio of 0.002 5. Therefore, Zn0.01Mg1.98SnO4:0.01Mn2+ can be a potential candidate of novel long afterglow phosphors, and hyperspectral imaging also provides new research approaches for the rational proportioning of luminescent materials.

Enhanced long afterglow luminescence of Sr2MgSi2O7: Eu2+, Dy3+ by NH4Cl

In this work, the effects of NH4Cl, NH4HCO3 and CTAB on the afterglow intensity and duration of Sr2MgSi2O7: Eu2+, Dy3+ were compared. It was found that NH4Cl could greatly improve the luminescent performance of Sr2MgSi2O7: Eu2+, Dy3+. The synthesized Sr2MgSi2O7:Eu2+, Dy3+ were characterized by XRD, SEM, EDS, infrared spectrum, fluorescence spectrum and afterglow decay curves. Maximum afterglow brightness can be obtained with 20% of NH4Cl and by sintering at 1100 °C for 1 h.

Photostimulated luminescence excited by infrared LEDs in CaS:Eu2+ red afterglow phosphors

Red photostimulated luminescence (PSL) at 650 nm appears under the excitation by using an infrared (IR) light-emitting diode at 940 nm in CaS:Eu2+ afterglow phosphors. The effect of doping of Dy3+ ions, alkali metal ions or Cl− ions in CaS:Eu2+ on afterglow or photostimulation is investigated. Afterglow temporal decays and thermoluminescence glow curves suggest that Dy3+ ions and alkali metal ions induce different types of defects in the phosphor, and enhance the afterglow independently. Doping of Cl− ions is found to enhance the photostimulation by the IR excitation. Even if the phosphor is irradiated with IR light for some seconds, the afterglow decay curve is the same as when it is not irradiated with IR light. Trap states responsible for the photostimulation are different from those responsible for the afterglow. The red photostimulation appears under the excitation at 940 nm, after the phosphor is left in the dark for 60 min. Its intensity is 68% of the red PSL generated after being left in the dark for 10 min. It is considered that the PSL decreases little, when the sample is kept in the dark.

A novel sustainable luminescent ABS composite material for 3D printing

The development of 3D printing composites with good photoluminescence and mechanical properties is a necessary condition for its practical application. Here, the long persistent phosphors Sr2MgSi2O7: Eu2+, Dy3+ were modified with 3-aminopropyltriethoxysilane(KH550), and the phosphors were grafted with ABS with peptide condensation reagent 0-(7-Azabenzotriazol-1-yl)-N,N,N',N'-tetramethyluronium hexafluorophosphate(HATU). The effects of phosphors on their photoluminescence and mechanical properties were evaluated. The structure and morphology of the phosphor were determined by X-ray diffraction and scanning electron microscopy, and the successful grafting of the phosphor with ABS was verified by Fourier transform infrared spectroscopy. The optical properties of the composites were evaluated by fluorescence spectroscopy and afterglow decay curve, and the mechanical properties were determined by tensile test. The results show that the luminescence properties and tensile strength of ABS are greatly enhanced with the increase of phosphor content. When 3 wt% grafted phosphor is doped, the luminescence strength, tensile load and tensile strength reach the maximum.

Repetitive afterglow in zirconia by pulsed near-infrared irradiation toward biological temperature sensing

Photoluminescence provides information about the surrounding environment. In this study, aiming to develop a non-invasive deep body-temperature sensing method, we investigated photoluminescence properties of afterglow zirconia (ZrO2) by pulsed near-infrared (NIR) light irradiation based on the biological temperature. Pulsed light irradiation produced optically stimulated luminescence, followed by afterglow, with the property of repeating 100 times or more. Furthermore, the basic principle of temperature measurement was demonstrated through afterglow decay curve measurements. The use of harmless ZrO2 as a sensing probe and NIR light, which is relatively permeable to living tissues, is expected to realize temperature measurements in the brain and may also facilitate optogenetic treatment.

Design, synthesis and mechanism of green afterglow phosphors Zn4B6O13:Mn2+ doped with Ln3+ (Ln = Sm, Yb, Eu) guided by VRBE

In this work, the construction of host referred binding energy (HRBE) diagram and vacuum referred binding energy (VRBE) diagram is described in detail. The energy gap of Zn4B6O13 is calculated by diffuse reflectance spectroscopy and the energy level positions of Eu3+ in VRBE are determined by the charge transfer (CT) band of Zn4B6O13 doped Eu3+ to construct a complete lanthanide ions VRBE diagram. According to the constructed VRBE of Zn4B6O13 system, novel long-afterglow phosphors Zn4B6O13:Mn2+ co-doped with Ln3+ (Ln = Sm, Yb, Eu) is designed and synthesized successfully. The influence of B2O3 contents on the crystal structure and luminescence of the Mn2+ doped zinc borate phosphors were analyzed by XRD and emission spectra. Photoluminescence excitation and emission spectra, persistent luminescence spectra and afterglow decay curve indicate that the doping of lanthanide ions Sm3+ and Yb3+ prolonged the afterglow duration of green emission of Mn2+ effectively. The fitting results of persistent luminescence spectra is consistent with the fast decay process of afterglow decay curve. The energy level depths of Sm3+ and Yb3+ traps obtained by thermoluminescence analysis are 0.49 eV and 1.12 eV respectively, which are in good agreement with the results calculated by VRBE. The energy level position of Sm3+ and Yb3+ below the conduction band (CB) are suitable trap depth, which can store and release electrons continuously. However, that of Eu3+ is too deep to enhance the afterglow. According to the VRBE theory, the mechanism of the electron trap is satisfactorily explained, which is important to the subsequent research of system design and mechanism explanation of lanthanide ions doped long afterglow materials.

A new method for preparing cubic-shaped Sr2MgSi2O7: Eu2+, Dy3+ phosphors and the effect of sintering temperature

In this study, cubic phase Sr2MgSi2O7:Eu2+, Dy3+ long afterglow phosphors are prepared by slurry-assisted high-temperature solid phase (SHT) method. XRD patterns, SEM images, fluorescence spectra, afterglow decay curves, and thermoluminescence curves describe the luminescence properties and microstructure of cubic phase Sr2MgSi2O7: Eu2+, Dy3+ phosphors sintered at different temperatures. Results show that the sintering temperature affects the performance and structure of Sr2MgSi2O7: Eu2+, Dy3+ long afterglow phosphors. Phosphors sintered at 1200 °C show the highest degree of crystallinity and best afterglow properties. More importantly, sintering temperature is significantly lower and the performance is better than that of traditional high-temperature solid phase (HT) method. This method retains simple process characteristics of the HT and effectively reduces the energy consumption during synthesis, which is suitable for large-scale production.

Variable temperature persistent luminescence properties of phosphors with continuous traps

A yellow long persistent luminescence (LPL) phosphor of Sr3Ga4O9:Bi3+ were synthesized by a simple solid-state method. The luminescence properties have been investigated by photoluminescence (PL) spectra, LPL spectra, afterglow decay curves and thermoluminescence (TL) curves. A series of the excitation time and decay time dependent TL experiments have been conducted, and the trap characteristics of the phosphor were studied. The LPL can be detected more than 10 h, which is due to the fact that the feasible trap depth ensures the slow release of charge carriers. The results of LPL properties at variable temperature show that the phosphor has a broad application prospect in high-temperature environments.

Novel persistent phosphors Eu2+ - doped Sr5SiO4Cl6 with codopants Cr3+ and Sc3+ in high temperature application

New cyan long persistent luminescence (LPL) phosphors Sr5SiO4Cl6:Eu2+, Cr3+/Sc3+ (SSC: Eu2+, Cr3+/Sc3+) have been prepared. The LPL behaviors of the SSC are greatly enhanced through incorporating Cr3+ and Sc3+ ions as trap centers. The fluorescence and phosphorescence spectra of SSC:Eu2+, Cr3+/Sc3+ both show an asymmetric wide emission band at 446 nm, which is attributed to the 4f65 d1→4f7 transitions of Eu2+ions in two different Sr2+ sites. The LPL of the SSC:0.03Eu2+, 0.03Cr3+ can remain 11760 s above the identifiable intensity level (0.32 mcd⋅m−2) after 10 min of excitation (for SSC:0.05Eu2+, 0.05Sc3+, 4080s). In addition, the temperature-dependent afterglow decay curves also show good afterglow initial brightness at 443 K for SSC:0.03Eu2+, 0.03Cr3+ (for SSC:0.05Eu2+, 0.05Sc3+, 343 K). This research provides new blue LPL phosphors with potential applications in high temperature environment.

Design, Preparation, and Mechanical Property Study of Polylactic Acid/Ca2BO3Cl: Eu2+, Dy3+ Composite Material for 3D Printing.

To break through the simplification of three-dimensional printing (3DP) materials and realize the application of long-persistent phosphors in more fields, polylactic acid doped with Ca2BO3Cl: Eu2+, Dy3+ was prepared in this study. The structure of the mixtures was analyzed and determined by infrared spectroscopy. The luminescence properties of phosphors and the composites were studied by fluorescence spectra and afterglow decay curve measurements. The yellow light of the mixtures could be attributed to the 5d-4f energy level transition of Eu2+. After the excitation of 254 nm ultraviolet lamp, the luminance and duration of the composites could be clearly observed. The mechanical properties of the composite filaments were tested, including maximal force and elasticity modulus. In particular, the influence of humidity on mechanical properties was analyzed in detail. The prepared composite filaments were printed into hollow dodecahedrons and presented in this study. Therefore, the composites had great properties and might be expected to put into practical applications of 3DP technology.

Influence of co-doping germanium ions on the long persistent near-infrared luminescence of ZnAl2O4:Cr3+

A series of infrared long persistent phosphor samples of ZnAl2O4: Cr3+ with various doping concentrations of Ge4+ ions were synthesized via a high temperature solid state reaction method. Powder X-ray diffraction, persistent spectra, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Ge4+ ions on the luminescence in the spinel structure. The results define an optimal co-doping of germanium ions (2 mol%) in the ZnAl2O4: Cr3+ can enhance the afterglow time of the phosphor. With the increase of co-doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Thermoluminescence data emphasise there are modifications from the presence of the Ge ions. The phenomenon that the long-wave emission reaches the maximum value of the spectral spread before the short-wave signal provides interesting insights into the charge transfer process.

Eu2+, Dy3+: Sr2B5O9Cl, a new blue-emitting phosphor with long persistence

A new Eu2+, Dy3+: Sr2B5O9Cl phosphor with long persistence was synthesized in a reducing atmosphere by a solid-state reaction process. The pure-phase phosphor was obtained by calcination at 900 °C. The introduction of Eu2+ into the lattice of the matrix resulted in a broad blue emission centered at 423 nm, which was due to the characteristic 4f65d1 to 4f7 energy transfer of Eu2+ ions. Both Eu-doped and Dy/Eu-codoped phosphors displayed afterglow behaviors due to the electron traps generated by the incorporation of tri-valanced rare earth cations into the original Sr lattice sites. The afterglow of Eu2+: Sr2B5O9Cl and Eu2+, Dy3+: Sr2B5O9Cl phosphors showed standard double exponential decay behaviors, and the Eu2+/Dy3+ co-doped sample demonstrated better afterglow properties than Eu2+-doped one. A longer lifetime for the electrons was confirmed after the afterglow decay curve simulation. Based on the analysis of thermally stimulated luminescence (TSL), the difference in afterglow was attributed to the different trap concentrations induced by the Dy3+ (Eu3+) doping in the Sr2B5O9Cl matrix.

Improved luminescence and afterglow emission from Mn2+/Si4+ co-doped AlN by combustion synthesis method

An orange-red emitting Mn2+/Si4+ co-doped AlN phosphor was prepared by an efficient combustion synthesis method. Phase identification and structure characterization were performed using powder X-ray diffraction (XRD) and refined by the Rietveld method. Luminescence and afterglow properties of the AlN-based phosphors such as photoluminescence spectra (PL), CIE values, afterglow decay curves, thermoluminescence glow curves (TL) were systematically studied. Using the Tanabe-Sugano diagram, the Racah parameters B, C, and crystal field splitting parameter Dq of as-prepared phosphor were calculated to be 812 cm−1, 2168 cm−1, and 780 cm−1, respectively. The luminescence intensity and afterglow time were increased, respectively, by about 1.1 and 2.2 times after 3% Si4+ co-doping. Particular attention was paid to study the mechanism of Si4+ co-doping on improving luminescence properties using a combination of the above-mentioned method and X-ray photoelectron spectroscope (XPS). Two hypothetical stress cancellation and charge rebalance effects due to Si4+ co-doping were discussed. Besides, it was found a shallower trap level (0.56 eV, compared to 0.84 eV for those without Si4+ co-doping) was formed after the co-doping of Si4+, which results in enhanced afterglow performance.

Structural and optical properties of chromium doped zinc gallate long persistent phosphor prepared by surfactant assisted hydrothermal method

Herein, CTAB surfactant aided hydrothermal reaction was carried for preparing Cr3+ doped ZnGa2O4. Urea was used as fuel to continue the reaction. By fixing Cr3+ ions conc. to 0.5 mol%, the molar ratio of CTAB was varied. We used XRD, TEM, FTIR, PL, UV-VIS spectroscopy, decay kinetics, and afterglow decay experiments to characterize the samples. XRD data suggested a cubic phase matching with JCPDS card no. 00-038-1240. TEM images confirmed the formation of nanoparticles within the range 20-80 nm. The estimated band gap was around 4.8 eV. Excited by 227 nm UV lights elaborated a wide emission band extended from 600 to 800 nm and peaking at 696 nm. The afterglow decay curve showed a long persistent signal up to 1 hour after ceasing offthe excitation source.

Research on a persistent red tone fluorescent polyacrylonitrile fiber with coaxial structure based on Sr2MgSi2O7:Eu2+, Dy3+ and Y2O2S:Eu3+, Mg2+, Ti4+

In order to obtain a red fluorescent fiber with long persistent performance, Sr2MgSi2O7:Eu2+, Dy3+ and Y2O2S:Eu3+, Mg2+, Ti4+ phosphors were prepared by high-temperature solid-phase method, then the phosphors and Rhodamine B were spun into the Polyacrylonitrile (PAN) through coaxial wet-spinning. The structure and morphology of samples were characterized by the X-ray diffraction, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy and particle size analyzer. Fluorescent properties were studied based on photoluminescence spectroscopy and afterglow decay curve. The data show that Sr2MgSi2O7 has blue broadband emission due to the electronic transition of Eu2+, and the Y2O2S has red linear emission spectrum because of the electronic transition of Eu3+.The analysis results reveal that the excellent afterglow performance of Sr2MgSi2O7 plays a significant role in the secondary excitation. Rhodamine B was added in the coaxial fiber as a red light compensator through transferring the blue light to red fluorescence.

The influence of doped Cr ions on the luminescence properties of infrared long persistent phosphor ZnAl2O4 with the substitution of Ge ions

A series of Zn1·8Al1.6Ge0.2O4: Cr3+ x mol% (x = 0.5, 1, 1.5, 2, 2.5, 3) phosphors were synthesized via a high temperature solid state reaction. It was shown in the previous study that suitable germanium substitution in the original ZnAl2O4: Cr3+ infrared long persistent phosphors can enhance the afterglow time. In this paper, powder X-ray diffraction, afterglow decay curves, photoluminescence and isometric thermoluminescence spectra were collected to identify the influence of the Cr ions on the luminescence in the spinel structure. With the increase of doping, the diffraction peaks shift to the shorter angles which confirm a swelling of the crystal cell. Meanwhile, according to the photoluminescence, the excitation emissions of Cr3+ shift which respond to the structural changes. The Stoke and anti-Stoke lines of Cr3+ infrared emission are noticeable for these samples and the dependence of these lines with temperature is demonstrated. Both thermoluminescence (TL) and afterglow results prove that 1.5 mol% Cr is the optimized doping concentration. All the results indicate that with a suitable concentration, Zn1·8Al1.6Ge0.2O4: Cr3+ could be prepared as an excellent infrared long afterglow phosphor and the emission lines of Cr ions are excellent probe ions that record structural changes.

PREPARATION OF WATER-SOLUBLE SiO2 COATING Sr2MgSi2O7:Eu2+ , Dy3+ FOR CELLS IMAGE

In the present study, afterglow materials of SiO2 coating Sr2MgSi2O7: Eu2+ , Dy3+ (SiO2-PLNPs) of good water solubility were prepared by hydro-thermal co-precipitation method. Effects of SiO2 coating on the luminescence property, afterglow performance and water solubility of SiO2-PLNPs have been discussed by contrast with Sr2MgSi2O7: Eu2+ , Dy3+ (PLNPs) phosphor. The phase structure examined by X-ray diffraction (XRD) and both them was tetragonal Sr2MgSi2O7. From the excitation spectrum, they two can be excited by light with a wavelength of 275 nm and 355 nm. Subsequently emission peak was recorded at 470 nm. The afterglow decay curves of the PLNPs and SiO2-PLNPs showed that optical signal can be detected with a persistent time of 2 h. Micro structure of PLNPs and SiO2-PLNPs were characterized by scanning electron microscope (SEM) and transmission electron microscopy (TEM) which demonstrated the success for the surface coating. Suspension property test suggested SiO2-PLNPs have a good water solubility compared with PLNPs. The death rate of cells was less than 10 % when SiO2-PLNPs solution of different concentration treat mouse osteoblasts. Bright blue light spots were visible to the eye in the dark field when the above cells excited by a 470 nm excitation light.