Long-persistent Phosphor Research Articles

Luminescence behavior of Nd3+/Zr4+/3+ Co-activated ZrP2O7 persistent phosphor

The bluish-green long persistent phosphor (LPP) materials ZrP2O7:Nd3+ were synthesized in a reducing atmosphere by a conventional high-temperature solid state reaction. The XRD patterns, XPS survey scan, excitation and emission spectra, decay curves and thermoluminescence (TL) curves were used for investigating the structure and luminescence properties and mechanism of the materials. The emission band between 400 and 600 nm exhibit the characteristics of blue emission from d-d transitions of Zr and the characteristics of green emission from f-f transitions of Nd3+. The TL curves showed that the formation of high-concentration trap level at 337 K (0.73 eV) was mainly responsible for the LPP phenomenon of ZrP2O7:Nd3+ at room temperature.

Investigation of new color-tunable up-conversion phosphors and their long-persistent luminescence properties for potential biomedical applications

Long-persistent phosphor and up-conversion particles used for optical imaging continue to interest researchers. The present work identifies an Er3+ doped micro-sized CSAO-CSO mixed material that exhibits both up-conversion and persistent luminescence. The cross-relaxation that occurs among Er3+ ions contributes to enhancing the up-conversion intensity. The Tm3+/Ho3+ co-doped strategy was used to induce tunable up-conversion colors. The cross-relaxation process corresponding to the energy transfer mechanism was investigated via the luminescence lifetimes of Er3+. Moreover, the persistent luminescence and thermo-luminescence properties of CSAO-CSO: Er3+ were also investigated systematically. Our results combine the fields of up-conversion and persistent luminescence, which may support other explorations of new kinds of long-persistent and up-conversion materials.

Strontium substitution enhancing a novel Sm3+-doped barium gallate phosphor with bright and red long persistent luminescence

The blue/green long persistent phosphors (LPPs) have been commercially available, however, LPPs with red emission are relatively rare and there is still a strong desire for exploring excellent red LPPs. In this work, we developed a novel red LPP BaGa2O4: Sm3+ by solid-state reaction. Photoluminescence and long persistent luminescence (PersL) properties of this phosphor were investigated systematically. By studying the structural information of the BaGa2O4, a substitution strategy was implemented to enhance the PersL performance. The PersL properties are effectively improved due to the increasing concentration of traps caused by the substitution of Sr. With the help of the initial rise method, the existence of continuous and wide trap depth distribution in Ba0·94Sr0.06Ga2O4: 0.01Sm3+ were revealed. In addition, the photostimulated luminescence was also investigated. Ultimately, a possible mechanism is discussed.

Traps study of Ca2BO3Cl: Eu2+ Dy3+ long-persistent phosphor by electron paramagnetic resonance

Trap types of the yellow emitting long-persistent phosphor Ca2BO3Cl: [Formula: see text], [Formula: see text] were analyzed in this study. [Formula: see text] acting as luminescent centers produced a broad emission band located at 580[Formula: see text]nm, which ascribes to the 5d-4f transitions. Four kinds of traps in this afterglow phosphor were detected by thermoluminescence spectra. Electron paramagnetic resonance spectroscopy, which is a considerable testing method, was used to identify the traps caused by different reasons. Based on it, detailed processes and traps analyses were examined and discussed.

Endowing Cr3+-doped non-gallate garnet phosphors with near-infrared long-persistent luminescence in weak fields

Recently, Cr3+-doped gallates near-infrared (NIR) long persistent phosphors (LPPs) have been developed. However, Cr3+-doped non-gallate NIR LPPs is little. Herein, we propose two alternative hosts (Na2CaSn2Ge3O12 and Na2CaTi2Ge3O12) for Cr3+-doped non-gallate garnet NIR LPPs. These phosphors were fabricated by a conventional solid-state method in air atmosphere. Predominant cubic phase of these phosphors were observed in XRD patterns. Cr3+ ions locate at weak field in the two hosts and emit a broadband emission due to 4T2→4A2 transition which were illustrated by Tanabe-Sugano matrix and spectroscopic data, respectively. Systematic investigations of the nature of energy traps were carried out by thermoluminescence measurement. Finally, the long persistent luminescence mechanism is also reported in this study.

Li5 Zn8 Ga5 Ge9 O36 : Cr3+ , Ti4+ : A Long Persistent Phosphor Excited in a Wide Spectral Region from UV to Red Light for Reproducible Imaging through Biological Tissue.

Near-infrared (NIR) long-persistent phosphors (LPPs) have emerged as a potential solution for bio-imaging applications over the past few years. However, there are enormous challenges regarding their in situ application based on their dependence on short-wavelength excitation. In this paper, we report a multi-spectral excited NIR LPP, Li5 Zn8 Ga5 Ge9 O36 : 1.5 % Cr3+ , 0.5 % Ti4+ , which overcomes the limitations of functional processes in biological tissues and other complex systems. This LPP exhibits a high luminescent intensity and a long emission duration in the NIR region (700-800 nm). The applicability of this phosphor to tissue imaging is demonstrated experimentally. Its persistent luminescence (PersL) can easily penetrate approximately 2 mm of pork flesh. More importantly, this phosphor can be re-charged in situ using a red LED or laser diode array to provide renewed NIR PersL for biological tissues, which is beneficial for long-term biological tissue imaging applications with high signal-to-noise ratios. Systematic investigations of the nature of energy traps and PersL mechanisms are also reported in this paper.

A long-persistent phosphor Sr3MgSi2O8-1.5xNx:Eu2+,Dy3+,Mn2+ based on white LEDs applications

Abstract The N-doped Sr2.985Mg1-ySi2O8:0.005Eu2+,0.01Dy3+,yMn2+ (0 ≤ y ≤ 0.15) phosphors were designed to obtain long-persistent phosphors for white LEDs. All the samples were determined to be single-phase by XRD analysis. The particles show smooth surface with the help of the H3BO3 flux. The energy-dispersive X-ray spectrum indicates the existence of N element. Various Eu2+ emission centers have been gained and verified by the photoluminescence spectra and long-persistent emission spectra, and a red-shift of the Eu2+ emission was observed in the N-doped samples due to the nephelauxetic effect. In Eu2+-Mn2+ co-activated phosphors, tunable emission has been realized and an efficient energy transfer from Eu2+ to Mn2+ was found, which could belong to the dipole-dipole interaction mechanism. The optimal afterglow time was obtained in the Sr2.985MgSi2O7.76N0.16:0.005Eu2+,0.01Dy3+ sample, but doping Mn2+ reduces the afterglow time largely. The mechanism for the increase of luminescence intensity and afterglow time with N present was interpreted. The temperature-dependent luminescence was also evaluated.

Identifying a Cyan Ultralong Persistent Phosphorescence (Ba, Li) (Si, Ge, P)2O5:Eu2+, Pr3+ via Solid Solution Strategy

A series of cyan emission (Ba, Li) (Si, Ge, P)2O5:Eu2+, Pr3+ long persistent phosphors (LPP) were designed by solid solution strategy and synthesized by solid-state reaction; the crystal structure and photoluminescence of this long persistent phosphor have been analyzed systematically. Under 256 nm light excitation, the as-prepared (Ba, Li) (Si, Ge, P)2O5:Eu2+, Pr3+ presents a strong cyan emission located at 514 nm, and the decay time of samples can be extended to about 38 h (BaSi2O5:0.008Eu2+, 0.01Pr3+), 47 h (BaSi1.5Ge0.5O5:0.008Eu2+, 0.01Pr3+), and 56 h (Ba0.92Li0.08 Si1.92 P0.08O5:0.008Eu2+, 0.01Pr3+) after ceasing the excitation source. A number of excitation duration (1 s ≤ t ≤ 30 s)-, decay duration (10 min ≤ t ≤ 10 h)-, and temperature-dependent thermoluminescence experiments of (Ba, Li) (Si, Ge, P)2O5:0.008Eu2+, 0.01Pr3+ were conducted, revealing that the existence of shallow and deep traps caused by Eu2+ and Pr3+ ions in samples gives rise to the excellent LPP property. According to the experimental results, a feasible mechanism of persistent luminescence of (Ba, Li) (Si, Ge, P)2O5:0.008Eu2+, 0.01Pr3+ was proposed and illustrated in detail.

Crystal field modulation-control, bandgap engineering and shallow/deep traps tailoring-guided design of a color-tunable long-persistent phosphor (Ca, Sr)Ga4O7:Mn2+,Bi3+ .

In this paper, a new color tunable long persistent phosphor (Ca, Sr)Ga4O7:Mn2+,Bi3+ has been successfully synthesized via a high-temperature solid-state reaction. Crystal field modulation and band gap engineering controlled by Sr2+ substitution for Ca2+ realizes the color tunable Mn2+ emission from 580 to 556 nm. Guided by the tailoring of traps distribution, the long persistence luminescence (LPL) performance of CaGa4O7:Mn2+ is greatly enhanced to 33 times higher brightness and much longer persistent time through Bi3+ co-doping. Furthermore, aided by the Rietveld refinement method, steady/transient-state fluorescence and thermoluminescence (TL) techniques with the combination of DFT calculations, the crystal structure evolution, electronic structure, trap distribution tailoring, self reduction of Mn4+, and the related color tunable Mn2+ photoluminescence/enhanced LPL properties are systematically characterized. Finally, a schematic diagram is proposed for a detailed illustration of the photoluminescence and LPL mechanisms.

Commendable Pr3+-activated Ba2Ga2GeO7 phosphor with high-brightness white long-persistent luminescence

Novel white long-persistent phosphor Ba2Ga2GeO7:Pr3+ was synthesized and characterized by its structural information, photoluminescence and long-persistent luminescence properties.

Photoelectric engineering of bifacial dye-sensitized solar cells beyond sunny days

The development of weather-independent photovoltaics is a promising strategy for persistently generating electricity in daytime and night. Herein we build a category of multi-energy integrated bifacial solar cells by making long persistence phosphors (LPPs) tailored transparent counter electrodes. The optimized cell with green-emitting transparent polypyrrole-graphene/PtCo achieves a maximized power conversion efficiency of 8.59% under a simulated sun irradiation (100 mW cm−2, air mass 1.5 global) as well as a dark efficiency of 29.68% when ceasing solar illumination. Moreover, the newly launched photovoltaics can persistently generate power lasting for hours in the dark environments. The current work demonstrates a predictable application of photoelectric engineering for persistent energy harvesting free of sun illumination in future.

Sonochemistry-assisted black/red phosphorus hybrid quantum dots for dye-sensitized solar cells

The co-sensitization of mesoscopic TiO2 anode is a promising solution to wide-spectra dye-sensitized solar cells (DSSCs) with improved power conversion efficiency. Quantum dots are featured with tunable bandgaps, small sizes and high absorption coefficients, therefore they are always combined with state-of-the-art organic dyes for co-sensitized solar cells. We present here the sonochemistry-assisted synthesis of hybrid black/red phosphorus quantum dots (BP/RPQDs) for DSSC applications. The preliminary results demonstrate that hybrid BP/RPQDs have prolonged recombination lifetime of photogenerated carriers and light-response from ultraviolet to visible and even near-infrared (NIR) region. Upon assembly into liquid-junction DSSCs, the devices with BP/RPQDs-only and BP/RPQDs-N719 co-sensitizer achieve efficiencies of 0.12% and 8.02% in comparison with 7.60% for N719-only solar cell. Using photofluorescent photoanode from mesoscopic TiO2 and long-persistence phosphor (LPP), the new-typed DSSC presents persistent power generation performances after ceasing simulated sunlight irradiation.

A novel near infrared long-persistent phosphor La2MgGeO6:Cr3+, RE3+ (RE = Dy, Sm)

A novel near infrared long-persistent phosphor La2MgGeO6: Cr3+ was successfully prepared. Near infrared emission originates from the 2E→4A2 transition of Cr3+ in strong crystal field. Due to the electric dipole-dipole interaction, the luminescence quenches when doping concentration of Cr3+ beyond 0.003. By co-doping Dy3+ and Sm3+, the long-persistent luminescence intensity is significantly enhanced, and the long-persistent luminescence time is also prolonged. The results of the thermoluminescence measurement show that there are two kinds of traps in La2MgGeO6:Cr3+ phosphors. The depths of two traps were calculated to be 0.796 and 1.200 eV, respectively. The co-doping of Sm3+ and Dy3+ has a great influence on deep traps and has little effect on shallow traps. The present investigation has important guiding significance for a deep understanding of the nature of traps, which has an important influence on the long-persistent luminescence of the phosphors.

Three-dimensional printing of hybrid organic/inorganic composites with long persistence luminescence

Additive manufacturing (AM) techniques allow for the construction of sophisticated and hollow models based on the needs of customers, and they functionalize the raw materials (e.g., metal, polymer and ceramic) by structuring them. Here, we demonstrate a simple method for the realization of a three-dimensional architecture with long afterglow properties by curing organic resin doped with inorganic long persistent phosphors (LPPs) layer by layer through the stereolithography (SLA) technique. In our process, the LPPs made by solid state reaction were incorporated homogenously into a resin matrix and pre-designed 3D structures with the resolution of 0.1 mm were printed out. The high luminescence, considerable decay time and multi-color make these organic/inorganic composites reliable for applications in artifacts, crafts, toys and night indicators. It is also demonstrated that the resin containing SrAl2O4: Eu2+, Dy3+ phosphors can be used for fiber temperature sensing from 40 °C to 70 °C.

Tunable whole visible region color emission, enhancing emission intensity and persistent performance of a self-activated phosphor:Na2CaSn2Ge3O12

The composition and tunable luminescence properties of garnet phosphors are flexible because of their unique A3B2C3O12 structure. Garnet phosphors with tailored luminescence properties can be designed by varying in the A, B, and C cation sublattices. In this research, the self-activated long-persistent phosphor (LPP) Na2CaSn2Ge3O12 (NCSG) was successfully synthesized by a solid-state method. A series of dopants (Mn2+, Pr3+, Tb3+, and Dy3+) were selected as single-component emitters to tailor the emission color of the NCSG phosphor. NCSG emits in yellow at ~ 560 nm and in the near-infrared at ~ 790 nm with long-persistent luminescence (PersL). By doping with these ions, the PersL of the NCSG was significantly improved, and various colors covering the entire visible region from violet to the near-infrared were obtained. The trap types and depths were examined by electron paramagnetic resonance (EPR) and the thermo-luminescence (TL) glow curves. The EPR signals revealed that oxygen vacancies are the trap centers. The TL glow curves showed that the intrinsic and extrinsic luminescence centers both act as charge carrier recombination centers. Furthermore, the PersL mechanism of the NCSG and NCSG:R (R = Mn2+, Pr3+, Tb3+ and Dy3+) phosphors was discussed in detail. The strategies employed in this work can be an effective way to fabricate new multi-wavelength, garnet-based LPPs with potential applications.

Cr3+ activated Zn3Al2Ge3O12: a novel near-infrared long persistent phosphor

The near-infrared (NIR) long persistent phosphors have gained considerable attention owing to the potential applications in in vivo imaging. A novel NIR long-persistent phosphors Zn3Al2Ge3O12:Cr3+ was successfully synthesized by a high temperature solid-state reaction. The luminescent properties and the afterglow behaviors of the Zn3Al2Ge3O12:Cr3+ were investigated in detail. On the basis of thermoluminescence analyses, the mechanism of the persistent afterglow of the phosphors was also discussed briefly. The afterglow duration of this phosphor can last more than 12 h with the 650–750 nm emission range after stoppage of 254 nm ultraviolet light irradiation. Specifically, the persistent luminescence intensity and duration were regulated by changing Cr3+ doping concentration. All the results indicate that the Cr3+ activated Zn3Al2Ge3O12 has promising potential of practical applications.

Tunable NIR long persistent luminescence and discovery of trap-distribution-dependent excitation enhancement in transition metal doped weak-crystal-field CaZnGe2O6

A long persistent phosphor (LPP) CaZnGe2O6: Cr3+ has been rationally designed and successfully fabricated. The weak crystal field surrounding Cr3+ activator enables an afterglow emission band 700–1200 nm almost covering the biological transparency window. In this work, a feasible route of Mn2+ codoping is suggested to precisely control the spectral shape, which further meets the demand of wide range and steady response to different photo-detectors in the biological transparency window. An interestingly synchronous improvement of persistent duration of Cr3+ and Mn2+ emission center is discovered in this process. Meanwhile, this codoping technique also achieves the enhancement of afterglow-excitation intensity. The design approach employed here inherently involves the ingenious engineering for combining the isolated traps in Cr3+, Mn2+ singly doped LPP, and for forming a continuous-distribution trap in Cr3+, Mn2+ co-doped LPP according to the thermoluminescent measurement. The highlighted redeployment of trap distribution will opens a vista of potential avenues for LPP design, afterglow mechanism analysis and functionalized application of bio imaging.

Tunable long persistent luminescence in the second near-infrared window via crystal field control

Construction of an active composite as a biomarker with deeper tissue penetration and higher signal-to-noise ratio (SNR) is of great importance for the application in bioimaging. Here, we report a strategy for tuning the emission bandwidth and intensity via crystal field control in long persistent phosphors (LPPs). Ni2+-doped Zn1+ySnyGa2−x−2yO4 phosphors, with a tunable emission band peaking from 1270 to 1430 nm in the second near-infrared (NIR) window, have been successfully prepared. Such featured materials have the advantages of low absorption and scattering as well as more efficient tissue penetration. The emission spectra can be controlled by tailoring the local crystal field around the activator precisely via substitution of Zn and Sn for Ga. Moreover, with high resolution and weak light disturbance, these developed multi-band afterglow phosphors exhibit great application potential in advanced optical imaging.

Photoelectric engineering of all-weather bifacial solar cells in the dark

A promising but challenging problem for state-of-the-art solar cells is to persistently generate power in the daytime and dark. To address this profound issue, all-weather bifacial solar cells are built by combining long persistence phosphor (LPP) tailored fluorescent film with bifacial dye-sensitized solar cells. On behalf of the solar energy storage and fluorescent excitation behaviors of LPP phosphors, the so-called all-weather solar cells yield a maximized photoelectric conversion efficiency of 10.04% and a dark efficiency as high as 21%. Moreover, the newly launched all-weather solar cells with 32 modules can lighten a lamp, demonstrating a predictable application in future energy harvesting. The current work could also extend our knowledge to more advanced all-weather solar cells.

A novel rare-earth free red long-persistent phosphor: Mg2GeO4:Mn4+

Abstract Red-emitting long-persistent phosphor Mg 2 GeO 4 : Mn 4+ was prepared by a high-temperature solid-state reaction. The photoluminescence and afterglow properties of Mg 2 GeO 4 : xMn 4+ phosphors were studied systematically. Furthermore, to improve the afterglow performance, co-doped Re 3+ (Re = Pr, Er, Nd and Yb) ions into Mg 2 GeO 4 : 0.001Mn 4+ separately to adjust the trap depth or increase the trap density was performed. The duration of Mg 2 GeO 4 : 0.001Mn 4+ can be observed 30 min by naked eyes, and the initial brightness and afterglow duration are significantly improved after Re 3+ ions are doped respectively. Especially, the afterglow emission of Mg 2 GeO 4 : Mn 4+ , Yb 3+ can last for 2 h. This investigation shows up a rare Mn 4+ -doped long-afterglow phenomenon, and provides a new and efficient red afterglow material for potential application.