Afterglow Decay Curves Research Articles

Persistent luminescence in rare earth ion-doped gadolinium oxysulfide phosphors

A series of rare-earth ion-doped gadolinium oxysulfide phosphors Gd 2O 2S:RE 3+, Ti, Mg (RE = Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb) were synthesized by solid-state reaction. The excitation and photoluminescence spectra, afterglow spectra, afterglow decay curves and thermoluminescence spectra of the phosphors were examined. According to the afterglow spectra, gadolinium oxysulfide doped with rare-earth ions were classified into three groups. When rare earth ions such as Eu 3+, Sm 3+, Dy 3+, Ho 3+, Er 3+ and Tm 3+ were introduced into the Gd 2O 2S host, their characteristic emission as well as that from Gd 2O 2S:Ti, Mg were observed. In case of Yb 3+ and Nd 3+, only the broadband luminescence of Gd 2O 2S:Ti, Mg was obtained. Gadolinium oxysulfide doped with Pr 3+, Tb 3+ and Ce 3+ did not show afterglow emission. The calculated trap energy levels of the samples were compared. The role of Ti and Mg ions and a potential mechanism for persistent luminescence in the samples were discussed.

Preparation and Optical Properties of Long Afterglow Europium-Doped Ca ( Sr ) Al2Si2O8 Electrospun Nanofibers

-doped nanofibers with an average diameter of 500 nm were in situ synthesized by electrospinning and calcination in reduced ambience. X-ray diffraction results confirmed that the nanofibers were of the anorthite phase. An intense blue emission due to the transition of ions was observed in the nanofibers. The emission band shifted to the blue region with the substitution of Ca by Sr due to the change in the crystal field surrounding ions. The long afterglow decay curves of nanofibers contain rapid and slow components. By the co-doping of ions, the emission and long afterglow duration of nanofibers were improved remarkably. These , electrospun nanofibers with excellent emission and long afterglow properties were potentially applied in biological marker, display, sensor, etc.

Effects of Gd 3+ and Lu 3+ co-doping on the long afterglow properties of yellowish-orange phosphor Y 2O 2S:Ti 4+, Mg 2+

A new long afterglow phosphor Y 2O 2S:Ti 4+, Mg 2+ co-doped with Gd 3+ and Lu 3+ was synthesized by solid-state reaction in inert gas ambient. Its properties were systematically analyzed by X-ray diffraction (XRD), luminescence spectra, afterglow decay curves and thermoluminescence (TL) spectra. It was found that the long afterglow performance of Y 2O 2S:Ti 4+, Mg 2+ such as brightness and persistent time was largely improved when co-doped with Gd 3+ and Lu 3+. By analyzing the TL curve the activation energy E were calculated to be 0.64 eV for 388 K peak and 0.98 eV for 508 K peak, and the trap intensity related to 388 K peak is much stronger than that related to 508 K peak. The mechanism of the long afterglow was also discussed in this paper.

BCNO-Based Long-Persistent Phosphor

A BCNO-based long-persistent phosphor prepared by a low-temperature liquid-phase route is investigated. It shows a phosphorescence peak centered at and its afterglow decay curve fits . Electron paramagnetic resonance confirms the presence of a paramagnetic center, the signal of which exhibits a synchronized decay with the afterglow intensity. We assume that the phosphorescence arises from electrons that are thermally released from nitrogen vacancies and then fall into the carbon-related defects, giving the greenish emission. The BCNO material is a competitive long-persistent phosphor because it is derived from cheap raw materials.

CaAl[sub 2]O[sub 4]:Eu[sup 2+],Nd[sup 3+],Sr[sup 2+]: A White-Light Phosphor with Yellow-Green Long Afterglow

A CaAl 2 O 4 :Eu 2+ ,Nd 3+ ,Sr 2+ phosphor, with white light under irradiation and a yellow-green long afterglow, was prepared by the solid-state method. The emission spectra, afterglow spectra, and afterglow decay curve of the samples have been measured. It is found that the emission spectra under the irradiation of 400 nm are comprised of the blue-light emission (442 nm) and the yellow-green-light emission (538 nm), and the chromaticity coordinates were calculated to be x = 0.289, y = 0.341. After the irradiation source was removed, the blue emission decreased rapidly so that the white-light photoluminescence changed to the yellow-green afterglow and its persistent time was measured to be over 4 h.

Luminescence properties of a new Mn 2+-activated red long-afterglow phosphor

A new phosphor, CaZnGe 2O 6:Mn 2+, which emits red long-lasting phosphorescence centered at 648 nm upon UV light excitation, is prepared by the conventional high-temperature solid-state method and its luminescent properties are systematically investigated in this paper. XRD, photoluminescence, thermoluminescence spectra and afterglow decay curve are used to characterize the synthesized phosphor. This phosphor is well crystallized by calcination at 1150 °C for 3 h and possesses excellent performance. The color coordinate values of this phosphor are x=0.64, y=0.26 under 250 nm UV light excitation. Under 250-nm UV light irradiation, this phosphor shows obvious long-lasting phosphorescence that can be seen with the naked eye in the dark clearly after the irradiation source has been removed for more than 3 h. The possible mechanism of this red-light-emitting long-afterglow phosphor is also investigated based on the experiment results.

Long persistent light emitting diode indicators

An undergraduate laboratory was designed for undergraduate students to make long persistent light emitting diode (LED) indicators using phosphors. Blue LEDs, which emit at 465 nm, were characterized and used as an excitation source. Long persistent phosphors, SrAl2O4:Eu2+,Dy3+ (green) and CaS:Eu2+,Tm3+ (red), were used as light converters. These phosphors were coated onto the LEDs to produce an afterglow emission once the LEDs were switched off. The indication time of the indicators was extended due to the afterglow emission from phosphors. The emission spectra, afterglow emission spectra and afterglow decay curves of the LED indicators were measured by using a photodetector. These long persistent LED indicators have important applications in emergent situations when electrical power is unavailable.

Preparation and characterization of an Hf4+-doped zinc silicate long-lasting phosphorescent material

Hf4+-doped Zn2SiO4 phosphor emitting long-lasting cyan light was prepared by the conventional high temperature solid-state technique. The emission spectrum of the Hf4+-doped phosphor exhibits one broad band peaking at 471 nm in the visible region excited by 254 nm. The cyan-light afterglow can last about 40 min in darkness after being irradiated with 254 nm UV lamp for 10 min (250 mW/cm2). The afterglow decay curve can be fitted into a second-order exponential curve. The thermoluminescence (TL) curve shows two glow bands centered at about 386 K (0.61 eV) and 440 K (1.56 eV), respectively, with the lower trap energy level being responsible for the long-lasting afterglow emission. A possible mechanism of the long-lasting phosphorescence based on the experimental results is proposed.

Synthesis and Luminescence Properties of Cube-Structured CaSnO3 ∕ RE3 + ( RE = Pr , Tb ) Long-Lasting Phosphors

Uniform and cube-structured -doped phosphors have been successfully synthesized by a two-step approach including the room-temperature synthesis of precursors with the help of cetyltrimethylammoniumbromide surfactant and then converted to by calcination at . The decomposition process of the precursor, crystallization, and morphology of the as-synthesized phosphors have been investigated using thermal analysis, X-ray diffraction, and scanning electron microscopy. Furthermore, luminescence properties of phosphors, including photoluminescence, fluorescence lifetime, afterglow decay, and thermoluminescence, are also systematically discussed in this paper. The as-synthesized and doped CaSnO3 phosphors show intense luminescence under ultraviolet excitation. Moreover, the afterglow emission from phosphors lasts for more than after the ultraviolet irradiation source has been removed. Both the fluorescence and afterglow decay curves of the phosphors contain one fast decay component and another slow decay process. Thermoluminescence spectra indicate that the incorporation of ions into the host produces suitable trapping centers, which are the origin of the long-lasting phosphorescence phenomenon in this kind of material at room temperature.

Photoluminescence, afterglow and thermoluminescence in [formula omitted][formula omitted] irradiated with blue and UV light

The luminescence in SrAl 2 O 4 : Eu 2 + , Dy 3 + under continuous excitation is quite different from the “standard” intra-ion photoluminescence (PL) and gradually grows during hundreds of seconds before reaching the saturation (photo-charging effect). In this work, we report the behavior of photo-charging effect under the blue and UV light irradiation at temperatures between 20 and 370 K, as well as afterglow (AG) and thermoluminescence (TL) observed after the irradiation termination. At 20 K the photo-charging effect is absent. With increasing temperature the photo-charging effect appears as a result of PL decreasing due to competitive trapping process with activation energy of 0.17 eV. The AG decay curves are described well by the Becquerel's law with the exponent close to 1. The AG decay time is about 10–50 s and practically does not depend on temperature. The TL glow curve exhibits at least seven partially overlapped peaks with maxima at 50, 65, 80, 155, 200, 250 and 290 K. The emission spectra of Eu 2 + consist of two bands at 450 and 520 nm. Both the bands are the same for the PL, AG and TL spectra, but their ratio depends on temperature and the luminescence type.

Effects of RE3+ as a co-dopant in blue-emitting long-lasting phosphors, Sr3Al10SiO20:Eu2+

A series of novel long-lasting phosphors, Sr3Al10SiO20:Eu2+,RE3+, were prepared and studied. Under UV irradiation, broad-band emission long-lasting phosphorescence located at 466 nm was observed in all of these phosphors at room temperature. The effects of RE3+ as a co-dopant in Sr3Al10SiO20:Eu2+ were discussed in conjunction with the afterglow decay curves and thermoluminescence (TL) spectra. Quantitative TL spectra revealed that the introduction of RE3+ ions into Sr3Al10SiO20:Eu2+ host produces a highly dense trapping level at appropriate depth (335 K), which is considered to be responsible for the long-lasting phosphorescence at room temperature.

White-light long-lasting phosphor Sr 2MgSi 2O 7:Dy 3+

A Sr 2MgSi 2O 7:Dy 3+ phosphor emitting long-lasting white light was prepared and investigated. Under the ultraviolet excitation, the emission spectra of Sr 2MgSi 2O 7:Dy 3+ are composed of a broad band peaking at 441 nm from the host and the characteristic emission of Dy 3+ peaking at 480, 575 and 668 nm, originating from the transitions of 4F 9/2→ 6H 15/2, 4F 9/2→ 6H 13/2 and 4F 9/2→ 6H 11/2 in the 4f 9 configuration of Dy 3+. After stopping the excitation, the afterglow spectra consist of only emissions from the transitions of Dy 3+ and the emission band from the host does not contribute to the afterglow spectra. The red-light emission peaking at 668 nm from the transitions of 4F 9/2→ 6H 11/2 is rather weak. Therefore, the afterglow spectra are composed of intense blue-light emission peaking at 480 nm and yellow-light emission peaking at 575 nm, showing white-light for human eyes. The white-light afterglow can last about 40 min in darkness after excitation with 254 nm for 10 min (250 μW/cm 2). The afterglow decay curves can be fitted into hyperbolic curve. The thermoluminescence curves show two thermoluminescence bands peaking at about 295 and 330 K, which are responsible for the long-lasting afterglow emission.

Effect of RE 3+ as a co-dopant in long-lasting phosphorescence CdSiO 3:Mn 2+ (RE=Y, La, Gd, Lu)

Effect of RE 3+ as a co-dopant in long-lasting phosphorescence CdSiO 3:Mn 2+ (RE=Y, La, Gd, Lu) has been investigated. A longer orange emitting phosphorescence phenomenon was observed in the co-doped CdSiO 3:Mn 2+,RE 3+ phosphors after exciting with ultraviolet (UV) light. The luminescence properties, including photoluminescence (PL) spectra and thermoluminescence (TL) spectra, as well as the afterglow decay curves, were studied. The results revealed that one of the origins of the improvement is due to nonequivalent substitution to produce more e-traps, and energy transfer from Gd 3+ to Mn 2+ to boost the performance of CdSiO 3:Mn 2+,Gd 3+. Role of RE 3+ co-doped into CdSiO 3:Mn 2+ matrix and the possible long-lasting phosphorescence process are discussed in this paper.

Spectra and long-lasting properties of Sm3+-doped yttrium oxysulfide phosphor

We reported, for the first time to the best of our knowledge, the Sm3+-doped yttrium oxysulfide phosphors has reddish orange long-lasting phosphorescence. The phosphor show prominent luminescence in reddish orange due to the electronic transitions of 4G5/2→6HJ (J = 5/2, 7/2, 9/2), the afterglow color of this type of phosphors is a mixture of the three above mentioned electronic transition emissions and have a little different when the concentration of the Sm3+ dopant changes. Synthesis procedure of the Sm3+-yttrium oxysulfide reddish orange phosphor through the flux fusion method with binary flux compositions was presented. The synthesized phosphors were analyzed using X-ray diffraction (XRD) to interpret the structural characterization. The XRD analysis result reveal that the Y2O2S:Sm3+ phosphor synthesized with a binary flux composition containing (S and Na2CO3 at a ratio of 1:1 at 30wt.% of total raw material) at 1050°C for 3h was in single-phase. Luminescence properties of the Y2O2S:Sm3+ long-lasting phosphor was analyzed by measuring the excitation spectra, emission spectra and afterglow decay curve. The mechanism of the strong afterglow from Y2O2S:Sm3+ was also discussed in this paper.

Luminescence of Bi 3+ and Eu 2+ double centers doped in CaS host

In this work, double-center-doped luminescent material CaS:Bi3+, Eu2+ was made via flux NH4Cl by sintering in excess sulfur environment. The sample had a purplish red net luminescent color. Excitation spectra at both red, 650 nm and blue, 487 nm were taken. The red emission from Eu2+ center was mainly come from the 4f65d1 absorption in the CaS host. The blue emission from the Bi3+ center on the other hand showed no big difference from the singly doped CaS:Bi3+ materials in excitation spectrum. Emission spectra were obtained at excitaton of 270 nm and 300 nm. Stokes shift was moved about 20-30 nm, under different point excitation. Emission peaks of both Bi3+ and Eu2+ centers appeared at 463 nm, 642.5 nm by 270 nm excitation and 487 nm, 620 nm by 300 nm excitation respectively. After-glow decay curves were also obtained and the shapes of decay curves are similar and it is due to the single hole-trap system by lattice defects.

Decay of delayed light with the diatom Phaeodactylum tricornutum

Intact cells of the diatom Phaeodactylum tricornutum do not show a smooth afterglow decay curve. After a sharp decline (0–150 msec), a maximum may occur after 4 sec at 17° or after 22 sec at 2°. This maximum is present after excitation with far red light of low intensity, which is absorbed primarily by photosystem I. It appears to be structure-bound: cell disintegration causes its disappearance, while the 150 msec afterglow component is much less affected. The maximum also disappears after addition of 3-(3′4′-dichlorophenyl)-1,1-dimethylurea (DCMU) or ammonium chloride, but it remains unaffected by addition of phenazinemethosulphate (PMS) or pyocyanin. Addition of DCMU results in a strong increase in the 150 msec afterglow when the cells are excited with far red light. The experiments suggest that a diffusion-limited energy transfer mechanism, depending on the physiological state of the cell, is responsible for the maximum.