Long-lasting Phosphorescence Research Articles

Green persistent luminescence excitable by multiple wavelengths in the CaSc2O4:Ce3+ phosphor co-doped with Mg2+

Calcium scandate (CaSc2O4), when substituted with a small amount of the activator ion Ce3+ to replace Ca2+, is a recently discovered green-emitting phosphor promising for solid-state lighting applications. The co-doping with aliovalent ions to compensate for the net positive charge, as induced by the Ce3+ dopants, is a common approach to change the defect structure and tune the performance of the phosphor, but the underlying mechanisms are unclear. Here we investigate the effect of co-doping with charge-compensating Mg2+ to substitute for Sc3+, using photoluminescence and thermoluminescence techniques. In comparison to the defect structure in Ce3+ doped CaSc2O4, the co-doping with charge-compensating Mg2+ leads to the formation of new traps. These traps are featured by activation energies in the range 0.58–0.64eV, can be emptied at room temperature and show green long-lasting phosphorescence after excitation at 454, 340, and 254nm, respectively. Analysis of the spectroscopic results in terms of a vacuum referred binding energy diagram allows us to reach at a plausible luminescence mechanism in {Ce3+/Ce3+Mg2+}-doped CaSc2O4.

A new blue long-lasting phosphorescence phosphor Mg2SnO4:Bi3+: synthesis and luminescence properties

In this article, we synthesized a new long-lasting phosphor Mg2SnO4:Bi3+ by traditional high-temperature solid-state reaction method. The structure and luminescence properties were characterized using X-ray powder diffraction, photoluminescence spectra, phosphorescence spectra, decay curves and thermoluminescence curves. The results show that the phosphor can exhibit blue emission corresponding to 3P1–1S0 transition of Bi3+ under UV light excitation. After ceasing the excitation, blue phosphorescence can be observed. For the optimal phosphor its blue phosphorescence could be observed by human naked eyes in the dark even after 3 h. The thermoluminescence analysis reveals that three kinds of trapping centers exist in the phosphor, of which the ones at 329 and 359 K are responsible for the long-lasting phosphorescence at room temperature. Bi3+ ions took the sites of Mg2+ and Sn4+ forming three different types of emitting centers, and yielding charged impurity defects which acted as charge trap centers and partly stored the excitation energy.

Fluorescence property of novel near-infrared phosphor Ca2MgWO6:Cr3+

A novel near infrared (NIR) emitting long-lasting phosphorescence (LLP) phosphors of Ca2MgWO6:Cr3+ were prepared by solid-state reaction in air. X-ray diffraction patterns showed that the obtained phosphors have a single-phase monoclinic structure and the incorporation of the dopants did not change the crystal structure. When excited at 371 nm, Ca2MgWO6:Cr3+ phosphors show characteristic broadband NIR fluorescence corresponding to the 4T2→4A2 transitions of Cr3+. The optimal Cr3+ doping concentration is 0.4% (mol). The critical distance between Cr3+ ions has been calculated and the concentration quenching type in Ca2MgWO6:Cr3+ was verified to be a dipole-dipole interaction. The optical spectra and the decay curves of the phosphors indicate that there exists efficient energy transfer from host to Cr3+ ions. The Ca2MgWO6:Cr3+ phosphors also exhibit NIR LLP phenomenon which is seldom presented in non-gallate phosphors. Finally, the possible fluorescence and LLP mechanism and possible energy transfer processes in Ca2MgWO6:Cr3+ phosphor are analyzed with simplified energy level diagrams.

Influence of oxygen vacancy on persistent luminescence in ZnGa_2O_4:Cr^3+ and identification of electron carriers

ZnGa2O4:Cr3+ is an outstanding near-infrared (NIR) long-lasting phosphorescence (LLP) material with afterglow duration of more than 5h, which is potentially applicable in bioimaging. The well-studied antisite GaZn • and ZnGa ′ defects are reported to serve as shallow traps responsible for the persistent luminescence. The less-studied but commonly available oxygen vacancy in this material may be associated with deep traps, which is barely investigated but of significance to influence the luminescence and LLP behavior. Moreover, persistent luminescence mechanisms associated with shallow and deep traps require identification of the carriers. This research attempts to reveal the detail of deep traps and the mechanism involved, with the assistance of photoluminescence (PL), thermoluminescence (TL), and alternating current (AC) impedance spectroscopy as well as density functional theory (DFT) calculations. Results show that the VO •• defects in the neighbor of Cr3+ could probably change the contents of antisite defects and result in variation of R/N2 ratio in PL and afterglow spectra. VO •• defects may also serve as the deep traps, which might agglomerate with Cr3+ and antisite defects to form cluster that is responsible for visible-light-stimulated LLP but with a negative effect. The research would be beneficial in understanding the common LLP phenomenon.

Oxygen-Vacancy-Induced Midgap States Responsible for the Fluorescence and the Long-Lasting Phosphorescence of the Inverse Spinel Mg(Mg,Sn)O4

Samples of inverse spinel Mg2SnO4 were prepared using a ceramic method, their phosphorescence phenomenon was probed by optical measurements, and its cause was explored on the basis of density functional theory calculations for model structures of Mg2SnO4 with oxygen vacancies VO. Mg2SnO4 exhibits long-lasting luminescence at two different wavelength regions, peaking at ∼498 and ∼755 nm. A Sn-VO-Sn defect plus a Mg vacancy VMg away from the VO generates the empty midgap states, σSn-Sn and σSn-Sn*, localized at the Sn-VO-Sn defect, while an oxygen vacancy VO between adjacent Sn4+ and Mg2+ sites creates a filled midgap state Sn2+ (5s2 lone pair) lying below the σSn-Sn level. The long-lasting luminescence at two different wavelength regions and the up-conversion photostimulated luminescence observed for undoped Mg2SnO4 are well explained by considering the σSn-Sn* level as the trapping level for a photogenerated electron.

Long-lasting phosphorescence with a tunable color in a Mn2+-doped anionic metal–organic framework

Based on a facile cation exchange with Mn2+ at different concentrations, the phosphorescence performance of the anionic metal–organic framework could be adjusted across an unusually wide range from blue to violet, white, yellow, orange and red.

Cyan emissive super-persistent luminescence and thermoluminescence in BaZrSi3O9:Eu2+,Pr3+ phosphors

We developed a novel long-lasting phosphorescence (LLP) material BaZrSi3O9:Eu2+,Pr3+.

Red long lasting phosphorescence of Eu3+ doped BiOCl semiconducting polycrystals

AbstractThe exploration of novel long lasting red phosphors is still of importance due to expected commercial applications and scientific interests. In this work, we reported the red long lasting phosphorescence (LLP) from Eu3+ doped BiOCl semiconductor polycrystals. The LLP property of the red phosphor is relatively weak due to less trap density, but the excitation band of LLP stems from the energy gap transition of semiconductor, offering experimental evidence for energy transfer between BiOCl semiconductor and Eu3+ ions. Although the afterglow duration of Eu3+ doped BiOCl was short temporarily, this work may open a novel kind of red LLP phosphors.

ChemInform Abstract: The Persistent Energy Transfer of Eu2+ and Dy3+ and Luminescence Properties of a New Cyan Afterglow Phosphor α‐Ca3(PO4)2:Eu2+, Dy3+.

AbstractThe long‐lasting phosphorescence (LLP) phosphor Ca3 (PO4)2:1%Eu2+,1%Dy3+ is prepared by calcination of a stoichiometric mixture of CaCO3, NH4H2PO4, Eu2O3, and Dy2O3 in a 5%H2/N2 reducing atmosphere (Al2O3 crucible, 1480 °C, 4 h).

Photoluminescence and afterglow of Mn2+ doped lithium zinc silicate

Novel green emitting long lasting phosphorescence (LLP) Li1.14Zn1.43SiO4:Mn2+ (LZS: Mn2+) was prepared successfully through a conventional solid-state reaction. Phase purity was checked by X-ray diffraction. The photoluminescence and afterglow properties of as-prepared phosphors were studied systematically by diffuse reflectance spectra, photoluminescence spectra, decay curves, afterglow spectra and thermoluminescence glow curves measurements. The photoluminescence spectra and LLP spectra indicated that LZS: Mn2+ phosphors exhibits green emission center at 526nm originated from 4T1→6A1 transition of Mn2+. The duration of Mn2+ doped Li1.14Zn1.43SiO4 phosphors can last about 1h. Thermoluminescence glow curves indicated that the LLP of LZS: Mn2+ phosphor was generated by the suitable trap depth. Based on the experimental results, a model was constructed to discuss the mechanism of afterglow briefly.

Competing roles of defects in SrAl2O4:Eu2+,Dy3+ phosphors detected by luminescence techniques

Abstract

Time-Resolved Detection of Fingermarks on Non-Porous and Semi-Porous Substrates Using Sr2MgSi2O7:Eu2+, Dy3+ Phosphors.

Eu(2+), Dy(3+) co-doped strontium-magnesium silicate phosphors, Sr2MgSi2O7:Eu(2+), Dy(3+) (SMSEDs), have shown great potential in optoelectronic device due to their unique luminescent property. However, their potential applications in forensic science, latent fingermark detection in particular, are still being investigated. In this contribution, SMSEDs were successfully employed to latent fingermarks on a variety of non-porous and semi-porous surfaces, including aluminum foil, porcelain, glass, painted wood, colored paper, and leather. All the results illustrated that this luminescent powder, as a long-lasting phosphorescence material (LLP), was an ideal time-resolved detection reagent of fingermark for elimination of background interferences from various difficult substrates, and offered a good contrast to allow their identification without the need to enhance the results compared to nanosized organic fluorescent powder.

Luminescence Properties of Eu 2+ -activated CaO-MgO-SiO 2 Long-lasting Phosphorescence Glasses

Luminescence Properties of Eu 2+ -activated CaO-MgO-SiO 2 Long-lasting Phosphorescence Glasses

A Zn based coordination polymer exhibiting long-lasting phosphorescence.

A new Zn(ii) based coordination polymer (CP) built by the cohesive pilling of 2D Shubnikov type layers is reported. This material exhibits time dependent multicoloured emission, part of which shows a persistent green phosphorescence visible for up to two seconds to the naked eye, which originates from multiple charge transfer mechanisms.

Effects of oxygen vacancies on luminescent properties of green long-lasting phosphorescent (LLP) material α-Zn3(PO4)2: Mn2+, K+

A green long-lasting phosphorescent (LLP) material α-Zn3(PO4)2: Mn2+, K+ was prepared with a joint method of combustion and conventional solid-state sintering. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL), and thermoluminescence (TL) techniques. The emission band of Mn2+ as luminescent centre was obtained at around 548nm (green). The emission of the spectrum was assigned to electronic transitions 4T1g–6A1g of Mn2+ ions. The afterglow emission of α-Zn3(PO4)2: Mn2+, K+ phosphor can be distinctly observed in the dark for more than 2h. The determination of the thermoluminescence (TL) curves shows that the introduction of K+ ions largely enhances the intensity of peak at 309K and the oxygen vacancies hold excited electrons. Oxygen vacancies catch and store excited electrons for some time to postpone their jumping back to ground levels, which will effectively extend the decay time of α-Zn3(PO4)2: Mn2+, K+.

The near-infrared long-persistent phosphorescence of Cr3+-activated non-gallate phosphor

Long persistent phosphors in the near-infrared (NIR) region have attracted much attention due to the potential application in in vivo imaging. A novel Cr3+-activated non-gallate phosphor was prepared by the Pechini method and characterized by photoluminescence, and long-lasting phosphorescence. Ca14Zn6Al10O35:Cr3+ phosphor gives a NIR long persistent luminescence (LPL) after the short UV-irradiation. The optimal concentration of Cr3+ for the LPP in non-gallate phosphor Ca14Zn6Al10O35:Cr3+ is experimentally about 0.5% and the afterglow time can last for 1h. Ca14Zn6Al10O35:Cr3+ is shown to be a new NIR persistent phosphor potentially suitable for in vivo imaging due to its 650–750nm emission range.

Red long lasting phosphorescence in Ca2Ge7O16:Sm3+ via persistent energy transfer from the host to Sm3+

A red long-lasting phosphorescence phosphor Ca2Ge7O16:Sm3+ was synthesized by a high temperature solid state reaction. The persistent energy transfer process from Ca2Ge7O16 host to Sm3+ was confirmed to be much more efficient than that in the photoluminescence process. The color of the persistent luminescence could be adjusted from blue to red with increasing concentration of Sm3+ accordingly. Based on the analysis of the thermoluminescence curves, it was found that Sm3+ doped Ca2Ge7O16 also provided a possibility to be a kind of photo-storage phosphor. Detailed mechanism were studied and illustrated.

Phosphorescence properties and energy transfer of red long-lasting phosphorescent (LLP) material β-Zn3(PO4)2:Mn2+,Pr3+

The red long-lasting phosphorescent (LLP) of β-Zn3(PO4)2:Mn2+,Pr3+ material was prepared through combustion and conventional solid-state sintering methods. The influence of Pr3+ ions on luminescence and LLP of Mn2+ in β-Zn3(PO4)2:Mn2+,Pr3+ phosphor was systematically investigated. The phosphor presented a strong photoluminescence peak at 620 nm attributed to the 4T1g→ 6A1g transition of Mn2+ ions in octahedral coordination. Red LLP was observed in β-Zn3(PO4)2:Mn2+,Pr3+ phosphors with persistence time for more than 2 h. It was found that the long persistent phosphorescent performance of Mn2+ such as brightness and duration was improved by the energy transfer from Pr3+ to Mn2+ when Pr3+ ions as sensitizers were doped into matrix. The fact that the TL peak at low temperature was largely enhanced in Mn2+, Pr3+ codoped β-Zn3(PO4)2 phosphor showed the significant increase of defect concentration with suitable depth. There existed two factors working together to be responsible for the enhancement of LLP performance in β-Zn3(PO4)2:Mn2+,Pr3+.

Investigation on Luminescence Properties of a Long Afterglow Phosphor Ca₂SnO₄:Tm³⁺.

A series of new long afterglow phosphors Ca2 SnO4:xTm(3+) were synthesized by using traditional solid-state reactions. XRD measurements and Rietveld refinement revealed that the incorporation of the Tm(3+) dopants generated no second phase other than the original one of Ca2 SnO4, which indicated that the dopants completely merged into the host. The corresponding optical properties were further systematically studied by photoluminescence, phosphorescence, and thermoluminescence (TL) spectroscopy. The results show that the Tm(3+)-related defects account for the bright bluish green afterglow emission from the characteristic f-f transitions of Tm(3+) ions. The bluish green long-lasting phosphorescence could be observed for 5 h by the naked eye in a dark environment after the end of UV irradiation. Two TL peaks at 325 and 349 K from the TL curves were adopted to calculate the depth of the traps, which were 0.45 and 0.78 eV, respectively. The mechanism of the long afterglow emission was also explored.

Influence of fluxing agent on the luminescence properties of SrAl2O4:Eu2+ nanophosphors

Eu2+ doped strontium aluminate nanophosphors are prepared by combustion method. The X-ray diffraction (XRD) and transmission electron microscope (TEM) studies showed the emergence of mixed phase for higher concentration of H3BO3. The effect of fluxing agent H3BO3 on the phase structure and on the luminescence properties; such as mechanoluminescence (ML) and photoluminescence (PL) properties of SrAl2O4:Eu2+ nanophosphors are investigated. The variation in fluxing agent H3BO3 influenced the PL and ML intensity and the maximum PL and ML intensity was observed for 7.5% H3BO3. The PL emission and ML spectra showed broad band at 515 nm corresponding to the 4f65d1 → 4f7 transition. The PL and ML for different amount of Eu revealed that the optimal concentration of Eu is 3%. An initial rapid decay followed by long-lasting phosphorescence was observed for the synthesized samples.