Persistent Luminescence Phosphor Research Articles

Photocatalysis in Darkness: Optimization of Sol-Gel Synthesis of NP-TiO2 Supported on a Persistent Luminescence Material and its Application for the Removal of Ofloxacin from Water

In the present work, a new photocatalyst based on a new persistent luminescence phosphor, PeLM, and NPs- TiO2 was synthesized and the synthesis was optimized using a chemometric approach. A solid-state synthesis was used to obtain the persistent luminescence material while a sol-gel synthesis was used to obtain anatase NPs-TiO2. Each sample was then characterized by means of XRD, SEM and BET analysis, while the photocatalytic activity was evaluated testing the percent degradation of a methylene blue aqueous solution. Two different kinds of experiments were performed on the optimized sample, using a continuous irradiation or halving it with darkness cycles. It’s been demonstrated that the PeLM acts as an internal source for TiO2, providing the excitation required for the photocatalysis and so allowing to continue photon absorption even in darkness conditions. The two materials were coupled by means of a solid-state synthesis, varying the ratio between the reagents (1, 6), the heating temperature (350, 550°C) and time (1, 6 hours) through a chemometric approach, in order to find the optimized values. Validating the model led to the conclusion that the parameters affecting the synthesis have no significant interactions among them. The obtained results demonstrated the real applicability of this coupled system in the removal of Ofloxacin from water solution as probe of emerging organic pollutants.

K4CaGe3O9:Mn2+,Yb3+: a novel orange-emitting long persistent luminescent phosphor with a special nanostructure

A novel orange-emitting long persistent luminescent phosphor, K4CaGe3O9:Mn2+,Yb3+, with a special nanostructure, has been successfully designed and synthesized.

LaAlO₃:Mn4+ as Near-Infrared Emitting Persistent Luminescence Phosphor for Medical Imaging: A Charge Compensation Study.

Mn4+-activated phosphors are emerging as a novel class of deep red/near-infrared emitting persistent luminescence materials for medical imaging as a promising alternative to Cr3+-doped nanomaterials. Currently, it remains a challenge to improve the afterglow and photoluminescence properties of these phosphors through a traditional high-temperature solid-state reaction method in air. Herein we propose a charge compensation strategy for enhancing the photoluminescence and afterglow performance of Mn4+-activated LaAlO3 phosphors. LaAlO3:Mn4+ (LAO:Mn4+) was synthesized by high-temperature solid-state reaction in air. The charge compensation strategies for LaAlO3:Mn4+ phosphors were systematically discussed. Interestingly, Cl−/Na+/Ca2+/Sr2+/Ba2+/Ge4+ co-dopants were all found to be beneficial for enhancing LaAlO3:Mn4+ luminescence and afterglow intensity. This strategy shows great promise and opens up new avenues for the exploration of more promising near-infrared emitting long persistent phosphors for medical imaging.

Thermoluminescence as a Research Tool to Investigate Luminescence Mechanisms.

Thermally stimulated luminescence (TSL) is known as a technique used in radiation dosimetry and dating. However, since the luminescence is very sensitive to the defects in a solid, it can also be used in material research. In this review, it is shown how TSL can be used as a research tool to investigate luminescent characteristics and underlying luminescent mechanisms. First, some basic characteristics and a theoretical background of the phenomenon are given. Next, methods and difficulties in extracting trapping parameters are addressed. Then, the instrumentation needed to measure the luminescence, both as a function of temperature and wavelength, is described. Finally, a series of very diverse examples is given to illustrate how TSL has been used in the determination of energy levels of defects, in the research of persistent luminescence phosphors, and in phenomena like band gap engineering, tunnelling, photosynthesis, and thermal quenching. It is concluded that in the field of luminescence spectroscopy, thermally stimulated luminescence has proven to be an experimental technique with unique properties to study defects in solids.

Enhanced Understanding of Persistent Luminescence in Submicron Particles of SrAl2O4:Eu2+,Dy3+

Bioanalytical applications such as in vivo imaging and point-of-care diagnostics have taken a special interest into the use of persistent luminescence phosphors. Their notable long luminescent decays and environmentally benign materials make them excellent candidates for testing platforms like lateral flow assays (LFAs). However, LFAs require particle sizes that range from 250 nm to 500 nm for adequate spontaneous flow without being subject to gravitational sedimentation or clogging of the assay due to large particle agglomerates. Synthesis methods to produce submicron particle sizes of these materials are widely studied and have shown successful reduction in size. Nevertheless, the shortfall of many of these methods is a lack of understanding on how reduction in particle size affects optical properties, namely a potential significant loss of the characteristic long lifetimes. Here, commercially purchased SrAl2O4:Eu2+,Dy3+ was wet milled followed by a series of centrifugal sedimentation steps to produce nearly monodispersed particles in the diameter (D) range of D ≤ 150 nm to 1000 nm. A detailed analysis of luminescent behavior as a function of particle size was studied on particles before milling, after milling and as a function of particle size. Furthermore, SrAl2O4:Eu2+,Dy3+ is widely known to decompose when exposed to an aqueous environment thus, making it necessary to encapsulate the particles in silica when being used in any bioanalytical testing format. Therefore, analysis of optical properties was also conducted on the varying particle sizes after being encapsulated in silica and compared to optically neutral 500 nm nanospheres exposed to the same optical characterization condition. This investigation gives valuable insight into the effects of post processing to achieve the necessary submicron particles required by bioanalytical applications, while also establishing a more robust understanding of how size impacts the unique characteristics of persistent luminescent phosphors.

Vacuum referred binding energy of 3d transition metal ions for persistent and photostimulated luminescence phosphors of cerium-doped garnets

The Y3Al5−xGaxO12(YAGG):Ce3+-Cr3+ persistent phosphor is one of the materials in which Cr3+ ions act as electron traps. The possibility of electron traps by other transition metal ions (TM3+, TM = Sc, Ti, V, Cr, Fe) was investigated and those electron trap depth was compared with each other. In the thermoluminescence (TL) glow curves, the YAGG:Ce3+ samples co-doped with different TM3+ ions show different TL glow peak temperatures (i.e. different electron trap depth). The estimated vacuum referred binding energy of TM2+ from the trap depth shows a zig-zag curve, which is found to be originated from the different 3d electron energies affected by a number of d electron, nuclear charge and crystal field splitting. Utilizing the obtained TM2+ zig-zag curve, a new persistent phosphor of Y3Al2Ga3O12:Ce3+-Sc3+ and a photostimulated phosphor of Y3Al2Ga3O12:Ce3+-V3+ were successfully developed.

Near-infrared persistent luminescence phosphors ZnGa2O4:Cr3 + as an accurately tracker to photothermal therapy in vivo for visual treatment

The photothermal therapy agents induced by 808 nm near infrared light laser have good potential for photothermal therapy (PTT) in vivo, with the advantages of harmless treatment, minimally invasion, high efficiency and deep tissue penetration. For the traditional photothermal therapy agents, however, it was impossible to track them in vivo because of the low signal-to-noise ratio, so we cannot conduct the extra near infrared light laser to radiate tumors sites accurately. Herein, we introduce a new complex: indocyanine green (ICG), near-infrared persistent luminescence (PL) phosphors ZnGa2O4:Cr3+ (ZGC) and mesoporous silica nanoparticles (MSNs) (ICG@mZGC nanoparticles) were assembled for long-lasting optical imaging to guide PTT. The results revealed that the novel nanoparticle, ICG@mZGC, could lower signal-to-noise ratio, enable highly sensitive optical detection during optical imaging-guided PTT and perform a good effect of photothermal therapy in vivo, and thus providing possibilities for mZGC to improve the localization precision of tumor sites in photothermal therapy in the body.

Long persistent properties of CaGa2O4:Bi3+ at different ambient temperature

AbstractA yellow long persistent luminescence (LPL) phosphor of CaGa2O4:Bi3+ (CGO:Bi) is developed, of which the LPL can be visually recognized (0.32 mcd m−2) over 36 hours after the removal of the excitation source. Furthermore, an excellent LPL performance above the room temperature and unusual thermal quenching behavior are observed. The thermoluminescence (TL) curves indicate that the continuity of the traps structure with different depths is a key factor in ensuring that carriers could be released from deep traps above room temperature successively. The work verifies unambiguously that the continuous defect‐state structure is beneficial to the LPL temperature resistant abilities, which would provide a reasonable approach to design new LPL phosphors in extreme environments.

A low-cost smartphone-based platform for highly sensitive point-of-care testing with persistent luminescent phosphors.

Through their computational power and connectivity, smartphones are poised to rapidly expand telemedicine and transform healthcare by enabling better personal health monitoring and rapid diagnostics. Recently, a variety of platforms have been developed to enable smartphone-based point-of-care testing using imaging-based readout with the smartphone camera as the detector. Fluorescent reporters have been shown to improve the sensitivity of assays over colorimetric labels, but fluorescence readout necessitates incorporating optical hardware into the detection system, adding to the cost and complexity of the device. Here we present a simple, low-cost smartphone-based detection platform for highly sensitive luminescence imaging readout of point-of-care tests run with persistent luminescent phosphors as reporters. The extremely bright and long-lived emission of persistent phosphors allows sensitive analyte detection with a smartphone by a facile time-gated imaging strategy. Phosphors are first briefly excited with the phone's camera flash, followed by switching off the flash, and subsequent imaging of phosphor luminescence with the camera. Using this approach, we demonstrate detection of human chorionic gonadotropin using a lateral flow assay and the smartphone platform with strontium aluminate nanoparticles as reporters, giving a detection limit of ≈45 pg mL-1 (1.2 pM) in buffer. Time-gated imaging on a smartphone can be readily adapted for sensitive and potentially quantitative testing using other point-of-care formats, and is workable with a variety of persistent luminescent materials.

Warm-white persistent luminescence of Lu3Al2Ga3O12:Pr3+ phosphor

A warm-white emitting persistent luminescence phosphor Lu3Al2Ga3O12:Pr3+ was synthesized by solid state method at 1600 °C in air. The refined crystal structure of Lu3Al2Ga3O12 host was solved by X-ray diffraction (XRD). The photoluminescence spectra, decay curve and thermoluminescence were investigated. It was revealed that the persistent luminescence originated from the f-f transitions of Pr3+ emitters at Lu3+ sites in LuO8 polyhedrons, and it showed white color due to the 3P0→3H4, 3P1→3H5, 3P0→3H5, 3P0→3H6, 3P0→3F2, 3P0→3F3 and 3P0→3F4 transitions of Pr3+ emitters in a wide range. The persistent luminescence of Pr3+ in this host could be promoted by f-d transition (278 nm) but f-f transitions, due to the different thermal activation energy. The persistent luminescence of the optimal sample could be actually recorded for 3 h by the definition of 0.32 mcd/m2 and was visible for more than 7 h by dark-adapted vision in darkness. The initial depth of the dominant shallow traps was calculated to be about 0.56 eV, which is suitable for persistent luminescence. The different roles of the shallow and deep traps on the persistent decay process were investigated. Accordingly, the persistent luminescence processes and mechanism of the as-synthesized Lu3Al2Ga3O12:Pr3+ phosphors were proposed.

Superlong and Color-Tunable Red Persistent Luminescence and Photostimulated Luminescence Properties of NaCa2GeO4F:Mn2+,Yb3+ Phosphor.

An excellent persistent luminescence (PersL) phosphor NaCa2GeO4F:Mn2+,Yb3+ has been synthesized by traditional solid-state reaction. By controlling the occupation sites of Mn2+ emitters, the PersL color of this phosphor can be optionally tuned in the red to green-yellow region, and the maximum spectral shift is more than 50 nm. Significantly, the red PersL can be measured for approximately 13 and 3 h (0.32 mcd/m2) and can be observed for more than 20 and 5 h with dark-adapted vision after exposure to ultraviolet irradiation and artificial sunlight, respectively. The crystal/electronic structure and photoluminescence/PersL properties of this phosphor have been investigated in detail. A series of the excitation temperature-dependent thermoluminescence experiments and the initial rising method have been conducted to study the trap properties of this phosphor. It reveals the reasons for the variation of PersL color, excellent red PersL, and degradation of green-yellow PersL. According to the results, the as-prepared NaCa2GeO4F:Mn2+,Yb3+ can be considered as an excellent red PersL phosphor, and it also has potential for application in optical storage.

Synthesis and Characterization of CaMgSi<sub>2</sub>O<sub>6</sub> Activated by Eu<sup>2+</sup>

Rare earth silicate based MnMgSi2O5+n (M = Ca, Sr or Ba and n=1-2) phosphors, have attracted interest of researchers due to their high efficiency as a host, excellent thermal and chemical stability and high brightness adding to their low cost. These phosphors showed great potential in various applications such as fluorescent lamps, white light emitting diodes, and display components. High temperature solid-state reactions are usually employed to synthesize those compounds. This paper proposes an alternative method of obtaining nanophosphor host based on Eu-doped CaMgSi2O6 (CMS:Eu), persistent luminescence phosphor. Sol gel technique combined to a modified molten salt method was used. The resulted powder was calcined for 3h under an atmosphere of 5% H2 and 95% Ar2. Phase identification by XRD and the measurements of photoluminescence (PL) and photoluminescence excitation (PLE) were performed. Single phased CMS:Eu with persistent luminescence characteristics was prepared.

Optimizing Blue Persistent Luminescence in (Sr1-δBaδ)2MgSi2O7:Eu2+,Dy3+ via Solid Solution for Use in Point-of-Care Diagnostics.

Inorganic persistent luminescent phosphors are an excellent class of optical reporters for enabling sensitive point-of-care diagnostics, particularly with smartphone-based biosensing devices in testing formats such as the lateral flow assay (LFA). Here, the development of persistent phosphors for this application is focused on the solid solution (Sr1-δBaδ)2MgSi2O7:Eu2+,Dy3+ (δ = 0, 0.125, 0.25, 0.375), which is prepared using a high-temperature solid-state reaction as confirmed by synchrotron X-ray powder diffraction. The substitution of barium for strontium enables control over the Eu2+ 5d-orbital crystal field splitting (CFS) as a tool for tuning the emission wavelength while maintaining luminescence lifetimes >9 min across the composition range. Thermoluminescence measurements of the solid solution provide evidence that trap states contribute to the persistent lifetimes with the trap depths also remaining constant as a function of composition. Time-gated luminescence images of these compounds are captured on a smartphone arranged in a layout to mimic a point-of-care test and demonstrate the viability of using these materials as optical reporters. Moreover, comparing the blue-emitting (Sr0.625Ba0.375)2MgSi2O7:Eu2+,Dy3+ and the green-emitting SrAl2O4:Eu2+,Dy3+ in a single LFA-type format shows these two compounds can be detected and resolved simultaneously, thereby permitting the development of a multiplexed LFA.

ChemInform Abstract: Nonequivalent Substitution and Charge‐Induced Emitter‐Migration Design of Tuning Spectral and Duration Properties of NaCa2GeO4F:Mn2+ Persistent Luminescent Phosphor.

AbstractCodoping of the title phosphor with Li+, Al3+, N3‐, Ga3+, or B3+ leads to red emission color and improves its duration properties.

Cr3+ doped Ca14Zn6Ga10O35: A near-infrared long persistent luminescence phosphor

The near-infrared persistent phosphors have attracted increasing attention due to the potential application in in vivo imaging. Exploring new materials to realize efficient near-infrared persistent luminescence is a goal of general concern. Ca14Zn6Ga10O35:Cr3+phosphor gives a near-infrared long persistent luminescence over 3h with the 650–750nm emission range after the short UV-irradiation. The afterglow behaviors such as the persistent luminescence, the trap depth distribution, the trap types and the underlying mechanism for persistent luminescence, were comprehensively surveyed by means of thermoluminescence methods and electron spin resonance spectra. In addition, Al dopant was introduced to redeploy the trap distribution in Ca14Zn6Ga10O35:Cr3+ phosphor. Compared with the well-known phosphor ZnGa2O4:Cr3+, Ca14Zn6Ga10O35:Cr3+ is proved to be a new NIR persistent phosphor potentially suitable for in vivo imaging due to its 650–750nm emission range.

Persistent Luminescent Nanocarrier as an Accurate Tracker in Vivo for Near Infrared-Remote Selectively Triggered Photothermal Therapy.

Optical imaging-guidance of indocyanine green (ICG) for photothermal therapy (PTT) has great latent capacity in cancer therapy. However, the conventional optical image-guidance mode has caused strong tissue autofluorescence of the living tissue, which leads to the accurate infrared light irradiation cannot be conducted. In this article, ICG and persistent luminescence phosphors (PLPs) coloaded mesoporous silica nanocarriers ((ICG+PLPs)@mSiO2) were first designed and prepared for persistent luminescent imaging-guided PTT. The (ICG+PLPs)@mSiO2 nanocarriers could significantly improve signal-to-noise ratio during luminescence imaging-guided PTT, making the PLP promising for improving the accuracy of the tumor site for photothermal therapy in vivo. This paper is likely to develop a new way for accurately regulating cancer cell death based on luminescence imaging-guided PTT selectively triggered by near-infrared (NIR)-remote.

Sunlight‐activated long persistent luminescent polyurethane incorporated with amino‐functionalized SrAl2O4:Eu2+,Dy3+ phosphor

AbstractAn amino‐terminated long persistent luminescent phosphor (Amino‐SrAl2O4:Eu2+,Dy3+) was prepared based on inorganic SrAl2O4:Eu2+,Dy3+ phosphor, chemically modified with 3‐aminopropyltriethoxysilane (KH550). Fourier transform infrared and X‐ray photoelectron spectral, thermogravimetric and scanning electron microscopic measurements confirmed the successful synthesis of Amino‐SrAl2O4:Eu2+,Dy3+. Then this amino‐functionalized phosphor was introduced into polyurethane (PU) through urea linkages, and the effects of the chemical combination of Amino‐SrAl2O4:Eu2+,Dy3+ and PU on the morphology, structure, storage stability, and mechanical, thermal and luminescent properties of the resultant long persistent luminescent polyurethane (LPLPU) were investigated. Compared with SrAl2O4:Eu2+,Dy3+/PU composites prepared by physical blending, the LPLPU shows better mechanical properties and storage stability due to the good compatibility of Amino‐SrAl2O4:Eu2+,Dy3+ with PU. More residues and higher initial decomposition temperature are observed because the interaction of the amino‐phosphor and PU delays the degradation. Study of the luminescent effect reveals that the LPLPU shows more than 10 h afterglow after cessation of the excitation light, and the brightness of green light in darkness is basically the same as that of LPLPU and SrAl2O4:Eu2+,Dy3+/PU. © 2016 Society of Chemical Industry

Effect of Si on near-infrared long persistent phosphor Zn3Ga2Ge2−x Si x O10:2.5 %Cr3+

Advanced long persistent near-infrared phosphors Zn3Ga2Ge2−xSixO10:2.5 %Cr3+ (x = 0, 0.6, 1, 1.4, 2) were synthesized by solid-state reaction method. The duration of afterglow can last more than 30 h after stoppage of the 365 nm ultraviolet light irradiation. Specifically, Si4+ substituting Ge4+ can increase the afterglow time but attenuate light emission intensity by introducing deep level of traps. We discussed the mechanism to balance the persistent luminescence intensity and afterglow time, which has significant potential for applications and future research of super long bright persistent luminescence phosphors.

Structure, long persistent luminescent properties and mechanism of a novel efficient red emitting Ca2Ga2GeO7:Pr3+ phosphor

A novel red emitting long persistent luminescent phosphor Ca2Ga2GeO7:Pr3+ (2217) was developed by solid state method at 1300 °C in air. The refined crystal structure of Ca2Ga2GeO7 host was solved. The intense red long persistent luminescence originates from the f-f transitions of Pr3+ centers at highly disordered Ca2+ sites in CaO8 polyhedrons. It can be properly recorded for 1.5 h by the definition of 0.32 mcd/m2 and is actually visible for more than 5 h by dark-adapted vision in darkness. At least one type of intrinsic lattice defects of the Ca2Ga2GeO7 host as proper shallow traps exists in Ca2Ga2GeO7:Pr3+ material and the depth of the traps is calculated to be 0.59 eV, which is very suitable for long persistent luminescence. It reveals that the Pr3+ dopants not only act as emitters but also increase the density of these significant intrinsic traps, resulting in the efficient persistent luminescence of Pr3+. The retrapping and tunneling effects are demonstrated to be responsible for the nonexponential and much slower decay behaviors in the late slow-decay stage (t > 300 s). A new parameter of threshold depth is firstly defined for the evaluation of the retrapping and tunneling effects and it is calculated to be 0.76 eV in this case by a classic multi-peak fitting method based on general-order kinetics. Finally, the long persistent luminescence mechanism of this Ca2Ga2GeO7:Pr3+ phosphor is proposed according to these investigation results.

A vivid example of turning waste into treasure: persistent luminescence of Ca2Ga2(Si,Ge)O7:Pr3+,Yb3+ phosphor tailored by band gap engineering

We exhibit a vivid example of turning waste into treasure for the development of persistent luminescence (PersL) phosphor.