Persistent Luminescence Properties Research Articles

Dynamics of Charges in Superlong Blacklight-Emitting CaB2O4:Ce3+ Persistent Phosphor

The optical and persistent luminescence properties of CaB2O4:Ce3+ phosphor are presented. The optical emission for excitation in the 250–340 nm wavelength region is dominated by two bands at 365 and 460 nm. Lifetime measurements suggested that the 365 nm emission band is due to interconfigurational Ce3+ 5d → 4f transitions. Upon excitation with a 254 nm UV lamp, a superlong persistent luminescence in the UVA1 region (340–400 nm, blacklight) was observed, lasting for at least 15 h, and with excellent reproducibility, which is perfectly suitable for phototherapy application. The initial-rise method was applied on the thermoluminescence glow curves to determine the trap distribution and trap depth. The results suggest that one distinct trap, with an activation energy of ∼0.52 eV, was solely responsible for the persistent luminescence in the CaB2O4:Ce3+ phosphor. The other traps had a quasi-continuous distribution, with activation energies between 0.56 and 1.15 eV. The proposed persistent luminescence and the...

Design and synthesis of up-converted persistent luminescence Zn3Ga2SnO8:Cr3+, Yb3+, Er3+ phosphor

The Zn3Ga2SnO8:1%Cr3+, 5%Yb3+, 0.5%Er3+ phosphor with remarkable up converted persistent luminescence in the near infrared spectral region has been rationally designed and successfully fabricated. This phosphor has been synthesized by incorporating up-converting ions Yb3+-Er3+ into a Zn3Ga2SnO8:Cr3+ near-infrared emitting persistent phosphor and followed by the sintering process. After the stoppage of excitation by a 980 nm laser, the phosphor emits long-lasting near-infrared persistent luminescence with emission peak centered at 696 nm. Furthermore, the dual-mode luminescence feature by combining upconvered persistent luminescence and persistent luminescence properties from a single Zn3Ga2SnO8:Cr3+, Yb3+, Er3+ phosphor is expected to have important implications for several fields, such as complexed visualization systems, biologic imaging, sensing.

Yellow Persistent Phosphor Ba13.35Al30.7Si5.3O70:Eu2+,Tm3+ from the Energy Regulation of Rare-Earth Ions.

The luminescence properties of Ba13.35Al30.7Si5.3O70:Eu2+ and Ba13.35Al30.7Si5.3O70:Eu2+,Tm3+ phosphors are presented. After being excited by a light source, Ba13.35Al30.7Si5.3O70:Eu2+,Tm3+ phosphors emit intense yellow long persistent luminescence covering the region from 450 to 700 nm, which can last about 8 h. Thermoluminescence curves were demonstrated to analyze the trapping nature of persistent luminescence. Tm3+ is added to improve the long persistent luminescence properties of phosphors. The mechanism of persistent luminescence has been studied.

Designing a novel red to near-infrared persistent phosphor CaMgGe2O6:Mn2+,Sm3+ based on a vacuum referred binding energy diagram.

In this work, we designed and successfully synthesized a novel germanate-based persistent luminescence (PersL) phosphor host, CaMgGe2O6, via a solid-state reaction. We constructed an empirical energy level scheme of the CaMgGe2O6:Ln2+/Ln3+ phosphors according to the Dorenbos model. Then, we successfully theoretically predicted the choice of the optimal codopant of CaMgGe2O6:Mn2+ phosphors using this empirical energy level scheme. As a result, after co-doping with Sm3+, the PersL intensity is increased 16 times and the time duration is effectively improved 52 times due to the high concentration of new traps. CaMgGe2O6:Mn2+,Sm3+ shows red to near-infrared long persistent emission located at 675 nm, which can be sustained for about 60 minutes above the recognizable intensity level (≥0.32 mcd m-2), and the persistence duration of samples was three times that of the red commercial phosphor Y2O2S:Eu3+. The experimental results coincide well with the theoretical predictions. These results demonstrate that the strategy concepts of this work are feasible for the design of persistent luminescence materials. Moreover, a possible afterglow mechanism is studied and discussed with the assistance of thermoluminescence (TL) curves.

Tunable trap depth for persistent luminescence by cationic substitution in Pr3+:K1−xNaxNbO3 perovskites

AbstractThe development of efficient red‐emitting persistent phosphor is still an ongoing challenge. In the search of persistent materials in red range, Pr3+ is a good candidate owing to its transitions between 1D2 and 3H4 state at about 612 nm. In this paper, we investigated the red persistent properties of Pr3+‐doped perovskite oxide ABO3, (A: K, Na and B: Nb), which can be elaborated as large single crystal. KNbO3:Pr3+ appears to have weak photoluminescence and no persistent luminescence. However, the cationic substituted compounds K1−xNaxNbO3:Pr3+ (x = 0, 0.4, 0.5, 0.7 0.9, 1) exhibit intense persistent luminescence, which increases steadily with increase in Na content. We correlated persistence behavior with the position of Metal‐to‐Metal Charge Transfer (MMCT) band, which plays crucial role in tuning of the trap depth. The MMCT band position decreases with the addition of Na contents and the thermoluminescence peak shifts toward higher temperature indicating the formation of deeper traps. This is in good agreement with the enhancement of the persistent luminescence suggesting that a proper tailoring of MMCT is needed to design efficient Pr3+‐persistent phosphors with better performance. A detailed analysis on the trap depth, bandgap energy, and persistent luminescence properties is reported tuning the composition in the K1−xNaxNbO3:Pr powder.

Enhanced persistent luminescence of LiGa5O8:Cr3+ near-infrared phosphors by codoping Sn4+

The near-infrared (NIR) long persistent phosphors LiGa5O8:Cr3+ have attracted considerable attention owing to the potential applications in medical imaging. A series of novel LiGa5O8:Cr3+ phosphors with different Sn4+ concentrations were successfully prepared by a high temperature solid-state reaction. The influence of codoping Sn4+ on photoluminescence, long persistent luminescence and thermoluminescence properties were systematically investigated. The results showed the persistent luminescence performance of phosphors was significantly enhanced after the incorporation of Sn4+ ions. Thermoluminescence spectra indicated that the incorporation of Sn4+ contributes to the formation of defects and increase the traps density, thus improving the persistent luminescence properties of LiGa5O8:Cr3+ phosphors.

Enhanced persistent red luminescence in Mn2+-doped (Mg,Zn)GeO3 by electron trap and conduction band engineering

The effect of Zn substitution on the persistent luminescence properties of MgGeO3:Mn2+-Ln3+ (Ln = Eu and Yb) red phosphors was investigated. The intensity of the persistent luminescence of the Eu3+ co-doped phosphors increased with increasing Zn content, whereas that of the Yb3+ co-doped samples decreased. For both series of lanthanide co-doped samples, the thermoluminescence (TL) glow peak shifted to the lower temperature side with increasing Zn content. These persistent luminescence properties were well explained in terms of lowering of the bottom of the conduction band relative to the ground state of the divalent lanthanide ions. Especially, in Eu3+ co-doped system, TL peak shifted from 520 K to 318 K by 50% Zn substitution. The persistent radiance of the (Mg0.5 Zn0.5)GeO3: Mn2+-Eu3+ sample at 1 h after ceasing UV light was 46 times stronger than that of MgGeO3:Mn2+-Eu3+, and 11 times stronger than that of ZnGa2O4: Cr3+ standard deep red persistent phosphor.

Phosphate glasses with blue persistent luminescence prepared using the direct doping method

Phosphate glasses with the composition (90NaPO3-(10-x)Na2O-xNaF) (mol%) with x = 0 and 10 were prepared with blue persistent luminescence (PeL) using direct particles doping method. Commercial CaAl2O4:Eu2+,Nd3+ microparticles (MPs) with blue PeL were added in the glass melt at a lower temperature than the melting temperature. The PeL properties of the glasses were related to the diffusion of Al from the MPs to the glass occurring during the glass preparation, which was found to depend on the temperature at which the MPs are added in the melt and also on the time before casting the melt after adding the MPs. The glass with x = 0 can be prepared with homogeneous PeL if the MPs are added at 575 °C. This Tdoping temperature can be reduced to 550 °C by replacing Na2O by NaF in the glass.

Investigation of luminescence quenching and persistent luminescence in Ce3+ doped (Gd,Y)3(Al,Ga)5O12 garnet using vacuum referred binding energy diagram

Optical properties of Ce3+:5d−4f luminescence in garnet compounds are strongly related to the energy locations of the excited 5d levels and the host conduction band (CB). By constructing the vacuum referred binding energy (VRBE) diagram including information on these energy location for GdyY3-yAl5-xGaxO12 garnet (GYAGG) from the measured spectroscopic data, the luminescence quenching and persistent luminescence properties of GYAGG:Ce3+(-Cr3+) were discussed. The quantum yield (QY) of Ce3+:5d−4f in GYAGG:Ce3+ is clearly related to the energy gap, ΔE5d1−CB, between the lowest 5d level and the bottom of conduction band in the constructed VRBE diagram. This result indicates that the luminescence quenching of GYAGG:Ce3+ is caused by the thermal ionization. For GYAGG:Ce3+-Cr3+ persistent phosphors, the depth of the electron trap formed by Cr3+ was remarkably changed from 0.27 to 0.69 eV by varying the Gd and Ga contents. The estimated VRBE value of Cr2+ in GYAGG can be used as effective value to predict the electron trap depth by Cr3+ in other oxide compounds as well as garnet hosts.

Porous GdAlO3: Cr3+, Sm3+ drug carrier for real-time long afterglow and magnetic resonance dual-mode imaging

Here, a kind of porous nanoparticles GdAlO3:Cr3+, Sm3+ (GAO:Cr,Sm) which own magnetic resonance and long persistent luminescent properties have been synthesized. The spherical morphology and narrow size distribution would allow the GAO:Cr,Sm nanoparticles to be utilised as a drug carrier and the drug release results indicate that the GAO:Cr,Sm drug carriers have an excellent drug sustained properties. Applying the Cr3+ and Sm3+ coped with gadolinium aluminate as the NIR persistent luminescence center and the energy transfer resonance from Gd3+ to Cr3+, these nanoparticles exhibit excellent NIR persistent luminescence at 732 nm under the UV irradiation of 254 nm and it can persist for about half an hour. In addition, they possess a longitudinal relaxivity (r1) value of 4.75 mM−1 s−1, which means that these nanoparticles could be applied for MR imaging as contrast agents. Carboxymethyl Chitosan was modified on the surface of GAO:Cr,Sm nanoparticles to make them owning excellent biocompatibility and low toxicity and these nanoparticles were successful to realize in vivo imaging. Hence, the well-defined nanoprobes of GAO:Cr,Sm exhibit great potential in biomedicine as trackable drug carriers and in vivo imaging agent due to the dual-model imaging property.

Nanohybrids with Magnetic and Persistent Luminescence Properties for Cell Labeling, Tracking, In Vivo Real-Time Imaging, and Magnetic Vectorization.

Once injected into a living organism, cells diffuse or migrate around the initial injection point and become impossible to be visualized and tracked in vivo. The present work concerns the development of a new technique for therapeutic cell labeling and subsequent in vivo visualization and magnetic retention. It is hypothesized and subsequently demonstrated that nanohybrids made of persistent luminescence nanoparticles and ultrasmall superparamagnetic iron oxide nanoparticles incorporated into a silica matrix can be used as an effective nanoplatform to label therapeutic cells in a nontoxic way in order to dynamically track them in real-time in vitro and in living mice. As a proof-of-concept, it is shown that once injected, these labeled cells can be visualized and attracted in vivo using a magnet. This first step suggests that these nanohybrids represent efficient multifunctional nanoprobes for further imaging guided cell therapies development.

Decomposition of persistent luminescent microparticles in corrosive phosphate glass melt

Findings on the decomposition of persistent luminescent (PeL) SrAl2O4:Eu2+,Dy3+ microparticles (MPs) in phosphate glass melt under static condition are reported. PeL phosphate glasses with the composition (50P2O5-10Na2O-40SrO) (in mol%) were prepared by adding the MPs in the glass melt. The decomposition of the MPs occurs during the preparation of the glass and leads to changes in the Eu2+ sites and to the formation of Eu3+ which decreases the PeL properties of the glasses. The decomposition of the MPs depends on the temperature at which the MPs are added in the melt and also on the time before casting the melts.

Direct low-temperature synthesis of ultralong persistent luminescence nanobelts based on a biphasic solution-chemical reaction

Here, we report the direct hydrothermal synthesis of 1D-based Zn2GeO4:Mn2+ persistent luminescent nanobelts (ZGO:Mn PLNBs). The ZGO:Mn PLNBs exhibit rapid growth rate, and nanobelts can be obtained after 30min of hydrothermal treatment. The persistent luminescence performance can be fine-turned upon prolonging the hydrothermal time. Furthermore, the doping ratio of Mn2+ exhibits influence on the persistent luminescence properties of ZGO:Mn PLNBs, and 2% doping of Mn2+ shows superior persistent luminescence with decay time of longer than 20min. The developed 1D-based ZGO:Mn PLNBs can be simply prepared with the hydrothermal method and show tunable morphology and persistent luminescence. We believe that this solid-state-reaction-free chemical approach avoids the current key drawback in regard to PLNMs development, and thus will promote the broad use of these unique nanostructured PLNMs in developing optical device for imaging.

Role of oxygen vacancies in long persistent phosphor Ca2Ga2GeO7: Zn2+

AbstractActing as the electron trap, oxygen vacancies can strongly influence the long persistent luminescence (LPL) properties were verified in Ca2Ga2GeO7: Zn2+ (CGGZ) phosphor. The existence of oxygen vacancies in this self‐excitation material was confirmed by a simple fluorescence probe method. The introduction of zinc ions promotes the generation of oxygen vacancies, as well as optimizes its LPL properties. Thermoluminescence (TL) analysis revealed that electrons in deep trap will effectively transfer to the shallow one via the bridge of interstitial zinc. Accordingly, a mechanism for PL and LPL in this Gallogermanates was provided.

Synthesis and optical properties of P5+ co-doped Ba3SiO5:Eu2+ orange persistent phosphor

By co-doping the P5+ ions into Ba3SiO5:Eu2+, we synthesized new orange persistent phosphor using cellulose assisted liquid phase precursor (LPP) method. The emission spectra showed a typically broad orange emission band centered at 575 nm attributed to the 4f65d1 → 4f7 transition of Eu2+ ions under 400 nm excitation source. The persistent luminescence property of Eu2+ doped Ba3SiO5 orange phosphor was enhanced by co-doping non-equivalent phosphorus ions into silicon sites. This enhancement can be explained by formation of the trapping center due to the charge compenstation. Consequently, the afterglow decay exhibited an orange emission for more than 5 min after irradiation at under 365 nm for 1 min.

How to tune trap properties of persistent phosphor: Photostimulated persistent luminescence of NaLuGeO4:Bi3+,Cr3+ tailored by trap engineering

We take the NaLuGeO4:Bi3+,Cr3+ as a typical example to show an effective approach to tune the trap properties of persistent phosphor as needed. An empirical law concerning the trap engineering is summarized based on the experimental results and a large number of references. Guided by this law, the trap properties of this material are effectively tailored by Cr3+ codopants, and consequently the degradation of the infrared-to-ultraviolet persistent luminescence is greatly reduced. The calculations and a serial of thermoluminescence experiments have been conducted to verify the effect of the trap engineering. The infrared-to-ultraviolet persistent luminescence and trap properties are investigated in details. It demonstrates that the proposed empirical law concerning the trap engineering is indeed valid and the NaLuGeO4:Bi3+,Cr3+ material is potential for photodynamic therapy.

Sol-Gel Synthesis of CaTiO3:Pr3+ Red Phosphors: Tailoring the Synthetic Parameters for Luminescent and Afterglow Applications.

Two sol–gel synthetic routes for the preparation of CaTiO3:Pr3+ red emitting phosphors were compared, with the aim of producing nanostructured materials with tailored luminescence/afterglow properties. The effect of the synthetic parameters, such as the addition of a stabilizer and calcination temperature, on the structural, morphological, and optical properties was investigated. The desired perovskite phase was obtained at a calcination temperature of 800 °C or higher. Although the use of acetic acid as the chelating agent leads to micrometric particles with heterogeneous composition, the presence of hydroxypropylcellulose (HPC) results in smaller, less aggregated particles as well as in a high phase purity. At the highest HPC content, surface Ca-rich impurities were detected, although no segregated Ca-rich phases were detectable by X-ray powder diffraction analyses. Luminescence properties were found to be positively related to the phase purity of the oxide, with the highest quantum yields at temperatures equal to or higher than 1000 °C. On the contrary, persistent luminescence properties were highest at intermediate calcination temperatures and for samples synthesized with acetic acid. Overall, a notable role of oxygen vacancies resulting from local Ca excess was observed, acting as trap levels promoting longer relaxation pathways. Thanks to the small-sized particles and best steady-state luminescent properties due to a substantial decrease of lattice defects, the HPC synthesis is a promising strategy for light-emitting diode applications. On the other hand, the acetic acid synthesis promoted a higher defect density, which is required for an efficient yield of light emission in the long time range and is thus more suitable for afterglow applications.

Vacuum Referred Binding Energy (VRBE)-Guided Design of Orange Persistent Ca3Si2O7:Eu2+ Phosphors.

Orange persistent phosphors of Ca3Si2O7 (CSO) doped with Eu2+ were strategically developed by codoping Sm3+ or Tm3+. First, a vacuum referred binding energy, VRBE, diagram of Ca3Si2O7 (CSO) was constructed from the measured spectroscopic data. By the zigzag curve of the divalent lanthanide ions in the VRBE diagram, Sm3+ and Tm3+ ions were predicted to be a suitable electron trap for the persistent luminescence. The initial persistent luminance of CSO:Eu2+-Sm3+ and CSO:Eu2+-Tm3+ was found to be 290 times and 9300 times stronger, respectively, compared with CSO:Eu2+. By optimizing Eu2+ and Tm3+ concentrations, the persistent luminescence duration on 0.32 mcd/m2 reached approximately 50 min in CSO:Eu2+-Tm3+. From the VRBE diagram and the persistent luminescence properties, we discuss the persistent mechanism including the charging process, detrapping process, and electron trapping centers.

Glowing synthetic chlorohectorite: The luminescent features of a trioctahedral clay mineral

Clay minerals are versatile materials with numerous industrial applications. Their unique layered structure can act as a host for many optically active species. The synthesis and luminescence properties of chlorohectorite clays are now reported for the first time. The synthesized clays are composed of quasi-circular nanoparticles with diameters around 20–30nm showing blue/green emission and persistent luminescence with a duration of ca. 5s. The luminescence features are associated with titanium impurities in the chlorohectorite structure. It is shown that Ti can act as activator ion even at low concentrations: the XRF and ICP-MS measurements of the chlorohectorite materials indicate a Ti concentration around 60 ppm originating from the precursors. The XPS measurements of the clay materials showed the Ti 2p3/2 signals at 457.8 and 458.9eV associated with Ti3+ and TiIV, respectively. The excitation spectra confirm Ti3+ as the luminescent center in the chlorohectorites through the bands at 287 and 370nm, related to the e−(O2−(2p))→TiIV charge transfer and the electronic transitions from the t2g to eg levels of Ti3+, respectively. The persistent luminescence properties are due to structural defects common for layered silicates.

Red persistent luminescence in rare earth-free AlN:Mn2+ phosphor

We investigated the persistent luminescence (PersL) properties of a rare earth-free Mn2+ doped AlN (AlN:Mn) red phosphor together with a commercial SrAl2O4:Eu2+, Dy3+ green persistent phosphor as a reference. Similar to its photoluminescence (PL) spectrum, the PersL spectrum of the AlN:Mn phosphor exhibited a red emission band centered at 600nm due to the Mn2+: 4T1(4G)→6A1(6S) transition with a relatively narrow full width at half maximum (FWHM) of 43nm. The luminance of AlN:Mn powders was 0.65mcd/m2 at 60min after ceasing ultraviolet (UV) illumination, and its duration upon 0.32mcd/m2 could reach over 110min. An extremely broad thermoluminescence (TL) glow curve was observed ranging from 100K to 600K and peaked at around 310K, indicating a wide trap distribution in this material.