Phosphorescence Phosphor Research Articles

Valence and Local Structure Analyses of Eu and Dy Ions in Sr2MgSi2O7:Eu, Dy Long Persistent Phosphorescence Phosphors Synthesized by Solid State Reaction

Valence and Local Structure Analyses of Eu and Dy Ions in Sr₂MgSi₂O₇:Eu, Dy Long Persistent Phosphorescence Phosphors Synthesized by Solid State Reaction

Hydrophilic Ultralong Organic Nanophosphors.

Ultralong organic phosphorescence (UOP), enabling of persistent luminescence after removal of external excitation light, shows great promise in biological applications such as bioimaging in virtue of antibackground fluorescence interference. Despite of good biocompatibility and outstanding phosphorescent properties, most current organic phosphors are hydrophobic with poor water solubility in the form of bulk crystal with large size, limiting their potential in the biological field. Here, a facile and versatile approach is provided to obtain nanoscale hydrophilic phosphorescent phosphors (HPPs) by physically loading ultralong organic phosphors into hollow mesoporous silica nanoparticles. The as-prepared HPPs can be well suspended in aqueous solution and effectively internalized by HeLa cells with very low cytotoxicity. Such HPPs are successfully applied for afterglow bioimaging in living nude mice with a very high signal-to-noise ratio up to 31. The current study not only provides a universal strategy to realize UOP in aqueous media but also demonstrates their great potential for biomedical purposes as an advanced imaging indicator with long-lived emission lifetime.

Sr2MgWO6:Cr3+ phosphors with effective near-infrared fluorescence and long-lasting phosphorescence

Cr3+-doped near-infrared (NIR) long-lasting phosphorescence (LLP) phosphors have drawn great attention for the promising application in unique bio-labels. Most of the studies are focused on gallate materials. Here we report a novel non-gallates NIR LLP phosphor Sr2MgWO6:Cr3+ that exhibit broadband emission at 700–1000 nm. X-ray powder diffraction, photoluminescence spectra, photoluminescence excitation spectra, LLP decay curves and thermoluminescence glow curves were determined to study the NIR LLP property and mechanism of Sr2MgWO6:Cr3+. Although Sr2MgWO6:0.4%Cr3+ gives the strongest NIR emission, the optimum content of Cr3+ in Sr2MgWO6 phosphor for LLP was 0.1%. Trap type and depth in Sr2MgWO6:Cr3+ were also discussed according to the thermoluminescence glow curves. Sr2MgWO6:Cr3+ phosphor is promising in optical information storage, night-vision surveillance, and in vivo bio-imaging.

Considerable improvement of Na2CaSn2Ge3O12:Eu3+ reddish orange long-persistent phosphorescence with Co-doping of Dy3+

A novel reddish orange long persistent phosphorescence was observed in Na2CaSn2Ge3O12:Eu3+ and Na2CaSn2Ge3O12:Eu3+,Dy3+ phosphors which were prepared using conventional solid-state method at 1250 °C in air. X-ray diffraction analyses demonstrate that all samples consist of Na2CaSn2Ge3O12 as the predominant phase. With the excitation of 318 nm, all the samples can emit reddish orange light, which is attributed to the 5D0→7F1 transition of Eu3+. The Dy3+ as co-dopants greatly prolong the phosphorescent persistence time of Na2CaSn2Ge3O12:Eu3+ phosphor. The persistent time of the persistence is 5 h, remarkable increased by 21-fold after the co-doping of 0.4 mol% Dy3+. The significant changes in the thermoluminescence curves demonstrated that the incorporation of Dy3+ into Na2CaSn2Ge3O12:Eu3+ not only enriched the types of traps, but also greatly increased the concentration of original traps (V″Ca,V″Na. It can be seen from the photoluminescence, long persistent phosphorescence and thermoluminescence spectra of all obtained samples that the optimal composition is Na2CaSn2Ge3O12:1.2%Eu3+,0.4%Dy3+. The possible mechanism of the reddish orange long persistent phosphorescence phosphor Na2CaSn2Ge3O12:Eu3+,Dy3+ is investigated.

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.

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).

Synthesis and Characteristics of SrAl2O4: Eu2+, Dy3+ Long Afterglow Phosphors by Polymerized Complex Method

SrAl2O4: Eu2+ and Dy3+ phosphorescent phosphors were synthesized using the polymerized complex method. Generally, phosphorescent phosphors synthesized by conventional solid state reaction show a micro-sized particle diameter; thus, this process is restricted to applications such as phosphorescent ink and paint. However, it is possible to synthesize homogeneous multi-component powders with fine particle diameter by wet process such as the polymerized complex method. The characteristics of SrAl2O4: Eu2+ and Dy3+ powders prepared by polymerized complex method with one and two step calcination processes were comparatively analyzed. Temperatures of organic material removal and crystallization were observed through TG-DTA analysis. The crystalline phase and crystallite size of the SrAl2O4: Eu2+ and Dy3+ phosphorescent phosphors were analyzed by XRD. Microstructures and afterglow characteristics of the SrAl2O4: Eu2+ and Dy3+ phosphors were measured by SEM and spectrofluorometry, respectively.

차선의 시인성 향상을 위한 SrAl2O4 : Eu2+,Dy3+ 축광 마이크로 캡슐화에 관한 연구

차선의 시인성 향상을 위한 SrAl₂O₄ : Eu²⁺,Dy³⁺ 축광 마이크로 캡슐화에 관한 연구

Organically modified clays as rheology modifiers and dispersing agents for epoxy packing of white LED

We develop a new class of polyetheramine-modified organoclays that enable the homogenous dispersion of inorganic phosphorescent phosphor powder, yttrium aluminum garnet Y3Al5O12 (YAG), in epoxy, which can then be used for packing of light-emitting diode (LED) devices. The organoclays are prepared from the ionic exchange reaction of sodium montmorillonite (Na+-MMT) with poly(oxypropylene) (POP) diamines of sufficiently high molecular weight, which are found to be effective for homogenizing YAG in the two-component epoxy system involving an anhydride curing agent and an aliphatic epoxy resin. By adding the POP-diamine-based organoclays, the viscosity of the anhydride/epoxy resins is greatly enhanced and the resin shows a non-Newtonian shear-thinning behavior. Because of the high viscosity that retards the molecular motion, the micrometer-scaled YAG particles can remain dispersed in the resins for a fairly long time without precipitation during the curing process. We investigate the rheological properties of the organoclays as the thickening agent and applied the organoclays to fabricate YAG particle-dispersed epoxy for packing of blue light LED that mixes the yellow light of the well-dispersed YAG particles to form uniform white illumination.

Hybrid coordination-network-engineering for bridging cascaded channels to activate long persistent phosphorescence in the second biological window.

We present a novel “Top-down” strategy to design the long phosphorescent phosphors in the second biological transparency window via energy transfer. Inherence in this approach to material design involves an ingenious engineering for hybridizing the coordination networks of hosts, tailoring the topochemical configuration of dopants, and bridging a cascaded tunnel for transferring the persistent energy from traps, to sensitizers and then to acceptors. Another significance of this endeavour is to highlight a rational scheme for functionally important hosts and dopants, Cr/Nd co-doped Zn1−xCaxGa2O4 solid solutions. Such solid-solution is employed as an optimized host to take advantage of its characteristic trap site level to establish an electron reservoir and network parameters for the precipitation of activators Nd3+ and Cr3+. The results reveal that the strategy employed here has the great potential, as well as opens new opportunities for future new-wavelength, NIR phosphorescent phosphors fabrication with many potential multifunctional bio-imaging applications.

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.

Tailoring of the trap distribution and crystal field in Cr3+-doped non-gallate phosphors with near-infrared long-persistence phosphorescence

We present a series of efficient near-infrared (NIR) Cr3+-doped non-gallate long-persistence phosphors (Zn2SnO4: Cr and Zn(2-x)Al2xSn(1-x)O4: Cr) and highlight their special optical characteristics of broad emission band (650-1200 nm, peaking at 800 nm) and long afterglow duration (>35h). In the context of materials selection, these systems successfully avoid the existing ubiquitous reliance on gallates as hosts in Cr3+-doped phosphorescent phosphors. Zn2SnO4 is employed as a host to take advantage of its characteristic inverse spinel crystal structure, easy substitution into Zn2+ and Sn4+ sites by Cr3+ in distorted octahedral coordination and non-equivalent substitution. In this work, Al dopant was introduced both to precisely tailor the local crystal field around the activator center, Cr3+, and to redeploy trap distribution in the system. Indeed, such redeployment permits band gap adjustment and the dynamic variation of the annihilation and the formation of defects. The results demonstrate that the method employed here can be an effective way to fabricate multi-wavelength, low-cost, NIR phosphorescent phosphors with many potential multifunctional bio-imaging applications.

A novel un-doped long lasting phosphorescence phosphor: SrZrSi2O7

A novel phosphor of un-doped SrZrSi2O7 material with blue long lasting phosphorescence which could be recorded for about 5400 s (0.32 mcd/m2) was developed. It revealed that both the emission centers and traps levels were related to the oxygen-deficient defects which were induced in reducing atmosphere. The filling and fading experiments indicated that the traps levels in SrZrSi2O7 were continuous in distribution. The influence of shallow traps on deep traps was investigated and the important role of the bridge effect was revealed. The un-doped SrZrSi2O7 material obtained in reducing atmosphere showed potential application as a cheap blue long lasting phosphorescence phosphor.

SrAl2O4: Eu2+, Dy3+축광안료의 고온안정성에 관한 연구

Oxide phosphorescent phosphor has an wide application in ceramic art and decoration due to its chemical and mechanical properties. Here, phosphorescent properties of strontium aluminate phosphor (SrAl₂O₄: Eu 2+ , Dy 3+ ) emitting yellowish-green light was investigated with thermal treatment at 1250 oC under air and reducing atmosphere. The characterizations of thermally treated samples were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive Xray spectroscopy (EDX), fluorescence spectrometer. SrAl₂O₄: Eu 2+ , Dy 3+ still showed a good phosphorescent properties after annealing process in reducing atmosphere, while phosphorescence of SrAl₂O₄: Eu 2+ , Dy 3+ annealed in air seriously degraded, due to oxidation of Eu 2+ to Eu 3+ ions. It was also observed that SrAl₂O₄: Eu 2+ , Dy 3+ annealed in reducing atmosphere emitted yellowishgreen light during 3 h after being exposed to sunlight.

Photocatalytic reaction characteristics of the titanium dioxide supported on the long phosphorescent phosphor by a low pressure chemical vapor deposition.

This study investigated the photocatalytic behavior of titanium dioxide (TiO2)-supported on the long phosphorescent materials. Nanocrystalline TiO2 was directly deposited on the plate of alkaline earth aluminate phosphor, CaAl2O4: Eu2+, Nd3+ by a low pressure chemical vapor deposition (LPCVD). Photocatalytic reaction performance was examined with the decomposition of benzene gas by using a gas chromatography (GC) system under ultraviolet and visible light (λ > 410 nm) irradiations. The LPCVD TiO2-coated phosphors showed active photocatalytic reaction under visible irradiation. The mechanism of the photocatalytic reactivity for the TiO,-coated phosphorescent phosphor was discussed in terms of the energy band structure and phosphorescence. The coupling of TiO2 with phosphor may result in energy band bending in the junction region, which makes the TiO, crystal at the interface to be photo-reactive under visible light irradiation. The fastest degradation of ben- zene gas occurred for the TiO,-coated phosphor prepared with 1 min deposition time (-150 nm thickness). The LPCVD TiO,-coated phosphor is also photo-reactive under darkness through the light photons emitted from the CaAl2O4 phosphor. In addition, the TiO2-coated phosphorescent phosphors were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

Luminescent properties of blue long-lasting phosphorescence phosphors Sr6Al18Si2O37:Eu2+,RE3+

A series of novel blue long-lasting phosphorescence phosphors Sr6Al18Si2O37:Eu2+,RE3+ (RE3+=Ho3+, Gd3+, Dy3+ and Pr3+) were prepared by the conventional high-temperature solid-state reaction in a reductive atmosphere. Their properties were systematically investigated utilizing X-ray diffraction (XRD), photoluminescence, phosphorescence and thermoluminescence (TL) spectra. The phosphors emitted blue light that was related to the emission of Eu2+ due to 5d-4f transition. Bright blue long-lasting phosphorescence (LLP) could be observed after the excitation source was switched off. For the optimized sample, the blue long-lasting phosphorescence could last for nearly 4 h in the light perception of the dark-adapted human eye (0.32 mcd/m2). The effects of RE3+ ions on phosphorescence properties of the phosphors were studied, and the results showed that the co-doping of RE3+ ions greatly enhanced the intensity of the peak around 315 K which was related to the long lasting phosphorescence of the phosphors at room temperature and consequently improved the performance of the blue phosphorescence such as intensity and persistent time.

A novel green long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+

A novel silicate long-lasting phosphorescence phosphor Ca14Mg2(SiO4)8:Eu2+, Dy3+ was prepared by high-temperature solid state reaction. Its properties were investigated systematically by powder X-ray diffraction patterns, Rietveld refinements, photoluminescence spectra, long-lasting phosphorescence spectra, phosphorescence decay curves, and thermoluminescence spectra. Under the excitation of 400nm, Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor exhibits green light with the peak at 505nm, which is attributed to the 4f65d1–4f7 electronic transition of Eu2+ ions. It is also found that Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor can emit green persistent phosphorescence after the irradiation of ultraviolet or visible light is stopped. And for the optimal sample, the green persistent luminescence can last for about half an hour. The co-doping of Dy3+ ions greatly enhances the intensity and duration of the persistent luminescence in Ca14Mg2(SiO4)8:Eu2+, Dy3+ phosphor. However, the peak position of the long-lasting phosphorescence spectrum is red shift compared to that of the photoluminescence spectrum, and the possible reason was analyzed. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was also discussed.

Luminescence properties of a new bluish green long-lasting phosphorescence phosphor Ca9Bi(PO4)7:Eu2+,Dy3+

A new long-lasting phosphorescence phosphor Ca9Bi(PO4)7:Eu2+,Dy3+ was synthesized by solid state reaction and its long-lasting phosphorescence properties were investigated for the first time. The X-ray powder diffraction, photoluminescence, long-lasting phosphorescence spectra, decay curves and thermoluminescence curves were measured. The Ca9Bi(PO4)7:Eu2+,Dy3+ phosphor exhibits an asymmetric emission centered at 475nm, which can be ascribed to the 4f65d1–4f7 electronic transition of Eu2+. For the optimized sample, the bright bluish green long-lasting phosphorescence could be observed for 5h by naked eyes after the excitation source was removed. The long-lasting phosphorescence spectra show that the co-doping of Dy3+ ions greatly enhance the intensity of the long-lasting phosphorescence. Meanwhile, the long-lasting phosphorescence mechanism of this phosphor was discussed. Based on our study, Dy3+ ions are suggested to increase the density of electron or hole traps so as to improve the performance of the bluish green phosphorescence of Eu2+, including the intensity and persistent time.

ChemInform Abstract: Tunable Blue—White—Red Photoluminescence and Long Lasting Phosphorescence Properties of a Novel Zirconate Phosphor: La2Zr2O7:Sm3+,Ti4+.

AbstractThe title long lasting phosphorescence phosphor is prepared by solid state reaction of ZrO2, La2O3, TiO2 (0.1, 0.5, 1 mol%), and Sm2O3 (0.1, 0.5, 1, 1.5 mol%) in a H3BO3 flux (air, alumina crucible, 1673 K, 10 h).

Blue photoluminescence and long lasting phosphorescence properties of a novel chloride phosphate phosphor: Sr5(PO4)3Cl:Eu2+

A novel blue emitting long lasting phosphorescence phosphor Sr5(PO4)3Cl:Eu2+ is synthesized by solid state method at 1223K in reducing atmosphere. The afterglow emission spectrum shows one broad band centered at 441nm due to the 5d–4f transition of Eu2+ at six coordinated Sr(II) sites and the color coordinates are calculated to be (0.149, 0.095) which is close to the light blue region. The excitation band is in 240–430nm and partly overlaps the solar irradiation on Earth's surface. The long lasting phosphorescence of the optimal sample doping by 0.1mol%Eu2+ can be recorded for about 1040s (0.32mcd/m2). Thermoluminescence shows that there are at least three types of traps corresponding to peaks at 340K, 382K, 500K, respectively. The filling and fading experiments reveal that the traps in Sr5(PO4)3Cl:Eu2+ are independent. The shallow traps (340K) essentially contribute to the visible long lasting phosphorescence, while the deep traps (382K and 500K) are proved to be very stable. Thus, the Sr5(PO4)3Cl:Eu2+ material shows potential applications as not only a long lasting phosphorescence phosphor, but also an optical storage material.