Green Persistent Luminescence Research Articles

Enhanced up-conversion persistent luminescence of Zn2GeO4:Mn phosphors by non-equivalent doping and sensitization of up-conversion nanocrystals

Up-conversion persistent luminescence (UCPL) nanoparticles have captured tremendous attention due to their unique optical operating performance such as the absence of auto-fluorescence and the charging capacity of near-infrared (NIR) light. However, the weak afterglow intensity as well as low duration limits their practical applications including multimode anti-counterfeiting and biological imaging, etc. Herein, typical green persistent luminescence (PersL) and photo-stimulated luminescence (PSL) of Zn2GeO4:Mn2+ phosphors were enhanced via non-equivalent Li+ co-doping, in which the preferred site selection of Mn2+ and Li + have been verified by using the first-principles theory. The possible luminescent enhancement mechanisms were proposed based on improving the oxygen vacancy density and promoting the formation of Mn4+ defect energy level in bandgap structure by non-equivalent doping of Li+. Interestingly, UCPL of Zn2GeO4:Mn2+,Li + can be achieved after charging of Vis to NIR light. It is worth noting that this UCPL can be further enhanced by the sensitization of NaYF4:Yb,Tm nanoparticles via simply mixing Zn2GeO4:Mn2+,Li+ and NaYF4:Yb,Tm under 980 laser stimulation. As a result, Zn2GeO4:Mn2+,Li+ phosphor exhibits the enhanced quintuple-mode luminescence including photoluminescence, PersL, PSL, photo-stimulated persistent luminescence and UCPL. In particular, the achieved NIR rechargeable UCPL hybrid phosphors exhibit enormous potential for higher order anti-counterfeiting and rewriteable data encryption and decryption applications.

Experimental and theoretical study on the green persistent luminescence phosphor Ca5Ga6O14:Bi3+

In this study, we developed a type of green persistent luminescence (PersL) material Ca5Ga6O14:Bi3+, which could be excited by UV light ranging from 270 nm to 360 nm with peak at 325 nm and exhibited a broad afterglow band peaking at 515 nm with the duration of about 11 min, which can be ascribed to the electron transitions between the 6s orbital and the 6p orbitals of Bi3+ ion. The thermoluminescence investigation and the First-principle calculation results revealed that the 6s orbital of Bi3+ was about 0.2 eV above the valence band maximum, while the 6p orbitals were 0.6–1.0 eV below the conduction band minimum. Moreover, we found that O vacancies and −2 charged Ga vacancies could form defect levels just above valence band and serve as the hole-trap centers, playing the key role in the process of the afterglow of Ca5Ga6O14:Bi3+. The possible afterglow mechanism was discussed in detail. This work offers an efficient way to construct Bi3+ doped PersL phosphors with desired properties.

Color-tunable persistent luminescence phosphor for multimode dynamic anti-counterfeiting

Using a solid-state approach, the persistent luminescence property in sodium yttrium silicate which was single-doped or co-doped by europium or cerium was studied. The orthorhombic structure with the space group P212121 could be indexed to all samples, according to X-ray powder diffraction. The luminescence characteristics of these phosphors, including photoluminescence, luminescence degradation, and temperature-dependent emission, were systematically investigated. Under UV (∼365 nm) irradiation, blue/green emissions with broad bands peaking at 450/510 nm attributed to the characteristic 5d→4f/4f65d→4f7 transitions of Ce3+/Eu2+ could be observed in Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+, respectively. Moreover, blue and green persistent luminescence was also observed in Ce3+ or Eu2+ single-doped samples. Thermoluminescence curve of Na3LuSi3O9:Eu2+, Ce3+ reveals that Na3LuSi3O9:Ce3+ and Na3LuSi3O9:Eu2+ have similar trap distribution. Tunable persistent luminescence can be realized via ratio control of Ce3+ and Eu2+. A possible afterglow mechanism was presented and discussed. The prepared materials have the potential of multimode dynamic luminescence, because they are highly sensitive to the composition, the excitation wavelength, and the detecting time. The outstanding abilities of Na3LuSi3O9:Ce3+, Eu2+ demonstrate the practical capability of this material for fingerprint identification and anti-counterfeiting.

Phosphor-in-glass with time-evolving multicolor luminescence for dynamic anticounterfeiting

The conventional luminescent materials used in the anticounterfeiting field generally exhibit unicolor output and a single-wavelength excitation mode, resulting in a poor anticounterfeiting effect. Herein, we successfully achieved a new transparent SrAl2O4:Eu2+,Dy3+/CaAlSiN3:Eu2+ phosphor-in-glass (PiG) with dynamic luminescence color variation from red to yellow in hundreds of seconds during the ultraviolet lamp irradiation and green persistent luminescence (PersL) after ceasing excitation. Additionally, the prepared PiG owns excitation wavelength- or doping weight ratio-dependent color-tunable luminescence. As a proof-of-concept experiment, the specially designed SrAl2O4:Eu2+,Dy3+/CaAlSiN3:Eu2+ PiG based flower patterns exhibit dynamic luminescence color variation under a simple ultraviolet lamp, and can be observed for quick discrimination. This work exploits a new perspective for the design of dynamic multicolor anticounterfeiting materials.

Glass-based composites comprised of CaWO4:Yb3+, Tm3+ crystals and SrAl2O4:Eu2+, Dy3+ phosphors for green afterglow after NIR charging

In this paper, we demonstrated the fabrication of new phosphate-based composites with green persistent luminescence after being charged with near-infrared light using the direct doping method. The composites are composed of a phosphate glass and phosphors. The 75NaPO3 − 25CaF2 and 90NaPO3 − 10NaF (in mol%) were the 2 glasses of investigation. The intense blue up-conversion emission between 450 and 500 nm upon 980 nm pumping is obtained by adding CaWO4: Tm3+, Yb3+ crystals in the glass melt before quenching whereas the green persistent luminescence is from the SrAl2O4:Eu2+,Dy3+ phosphors also added in the glass melt. The green persistent luminescence above 0.3 mcd/m2 is observed for ∼30 min after charging with 980 nm due to energy transfer between the upconverter crystals and the persistent luminescent phosphors. Here, the challenges related to the fabrication of such composites are discussed. While it is important for the blue UC emission to be intense to charge the SrAl2O4:Eu2+,Dy3+ crystals, we demonstrate that the glass matrix should not crystallize upon the addition of the different crystals. Additionally, the composites should remain translucent with limited light scattering for the blue UC emission to charge the persistent luminescent phosphors.

CaWO4:Yb3+,Tm3+ Crystals and SrAl2O4:Eu2+,Dy3+ Phosphors in Glass-Based Composites for Green Afterglow after NIR Excitation

Here, we present the preparation of composites with green persistent luminescence using melting process. The composites are phosphate glass (75NaPO3-25CaF2 and 90NaPO3-10NaF (in mol%)) with embedded phosphors: CaWO4: Yb3+, Tm3+ crystals with blue upconversion and SrAl2O4:Eu2+,Dy3+ with green persistent luminescence. Green persistent luminescence above 0.3 mcd/m2 can be seen for ~ 30 minutes after charging with 980 nm due to energy transfer between the blue upconverter crystals and the persistent luminescent phosphors. Challenges related to the fabrication of such composites are discussed.

Zn2SiO4: Mn2+, Yb3+ long afterglow materials prepared employing Zn-based coordination polymer as precursor: Properties, Mechanism and Application

An excellent green persistent luminescence (PersL) phosphor Zn2SiO4: Mn2+, Yb3+ was synthesized through a new method via reacting Zn-based coordination polymer particles with SiO2 submicrospheres. The structure properties including the phase purity, structural parameters and crystal structure were investigated in details. Morphological analysis revealed that Zn2SiO4: Mn2+, Yb3+ retained the morphology of SiO2 submicrospheres with diameter ∼200 nm. The PersL of Zn2SiO4: Mn2+ displayed a remarkably enhanced afterglow duration by codoping with Yb3+, in which the duration time prolonged from 5 min to 114 min (∼23 times) as compared with that of Zn2SiO4 host or singly Mn2+ doped. The depths of the traps responsible for PersL were estimated to be in the range of 0.696–1.112 eV, and an additional trap that are deemed to play a role for the improvement was discussed. The prepared phosphors were successfully used for the latent fingerprint visualization and exhibited high accuracy of fingerprint recognition. These findings not only provids a new synthetic approach for PersL materials with designated morphology and dimensions, but also indicates the product may find applications in advanced latent fingerprint identification, information storage and anticounterfeiting technology.

Near-infrared rechargeable glass-based composites for green persistent luminescence

The fabrication of Yb3+, Tm3+ co-doped oxyfluorophosphate glass-based composites, with green persistent luminescence after being charged with near-infrared light, is demonstrated. The mechanism responsible for the green afterglow after near-infrared illumination is unveiled. The composite is prepared using a modified melting process to limit the evaporation of fluorine during melting. Intense (blue and ultraviolet) up-conversion emission is obtained by optimizing the Yb2O3 and Tm2O3 concentrations. A heat treatment promotes volume precipitation of Yb3+, Tm3+ co-doped CaF2 crystals. Although the intensity of the blue up-conversion emission from the Tm3+1G4 level is lower in the highly Yb3+-concentrated glass-ceramic due to reverse energy transfer from Tm3+ to Yb3+, the heat treatment leads to an increase of the intensity of the emissions around 346 nm, 361 nm nm and 450 nm coming from the Tm3+1I6 and 1D2 levels. By combining the Yb3+ and Tm3+ ions with SrAl2O4:Eu2+,Dy3+crystals, green afterglow can be obtained after charging with near-infrared light.

Bioactive phosphate glass-based fiber with green persistent luminescence

The first biophotonic composite fiber with green persistent luminescence is reported. The composites were drawn from preforms prepared by remelting a bioactive glass with commercial persistent luminescent microparticles (SrAl2O4:Eu2+,Dy3+). The duration of the remelt step should be as short as possible to limit the decomposition of the micro-phosphors during glass preparation, as evidenced using electron microscopy coupled with elemental analysis. The presence of the phosphors in the glass inhibits the drawing of fibers with diameter below about 400 µm. Although the drawing process induces some changes in the Eu2+ ions’ local structure in the phosphors, the fibers still exhibit green afterglow. Despite the presence of the phosphors, the fiber still maintains its bioactive response, as characterized by the release of ions from the glass to the environment and the successive precipitation of a reactive layer within a dicalcium phosphate dehydrate composition.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO 2 Bioreduction

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO ₂ Bioreduction

Preparation of glass-based composites with green upconversion and persistent luminescence using modified direct doping method

New oxyfluorophosphate glass-based composites which exhibit not only green upconversion under 980 nm pumping but also green persistent luminescence (PeL) after being UV charged were successfully prepared using the direct doping method. The composites are composed of a glass-ceramic with Er3+ doped CaF2 crystals and of the persistent luminescent particles with the SrAl2O4:Eu,Dy composition. In the standard direct doping method, the glass melt is quenched few minutes after adding the PeL particles in the melt held at a temperature lower than the melting temperature. It is demonstrated that the direct doping method should be modified when preparing oxyfluoride glasses with PeL particles to limit not only the decomposition of the PeL particles in the glass but also the fluorine evaporation occurring during the glass preparation. Here, the composites were prepared by quenching the melt right after adding the PeL particles. The modified direct doping method allows the preparation of glass-based composites with strong green upconversion and homogeneous green persistent luminescence.

Near-Infrared Rechargeable Glass-Based Composite with Green Persistent Luminescence from New Yb3+, Tm3+ Co-Doped Oxyfluorophosphate Glasses

Near-Infrared Rechargeable Glass-Based Composite with Green Persistent Luminescence from New Yb3+, Tm3+ Co-Doped Oxyfluorophosphate Glasses

Low dose soft X-ray-controlled deep-tissue long-lasting NO release of persistent luminescence nanoplatform for gas-sensitized anticancer therapy

Nitric oxide (NO)-based gas therapy is emerged as a new adjunct anti-tumor treatment method, which has triggered a great research interest. Nevertheless, due to the short half-life of NO gas in vivo, it is of significance to develop NO-gas based gasotransmitter with controllable NO release for deep-tissue anti-tumor therapy. Herein, a novel soft X-ray activated persistent luminescence nanotransducer is designed for controllable and long-lasting NO release and deep-tissue anti-cancer therapy by integrating ZnGa2O4:Mn (ZGO:Mn) nanoparticles with light-responsive NO donor (RBS). With the merits of the ultra-low dosage (down to 0.9 mGy) soft X-ray activated persistent luminescence from small sized ZGO:Mn, continuous NO release is achieved for about 40 min after stopping the irradiation of X-ray. Moreover, the green persistent luminescence can be renewably activated by in-situ soft X-ray irradiation, leading to the repeatable long-lasting NO release in deep tissue (up to 24 mm). And the designed NO-releasing platform presents efficient in vitro and in vivo anti-cancer therapy. Therefore, the designed persistent luminescence-based NO gasotransmitter provides a new NO-releasing strategy for depth-independent gas-sensitized therapeutic applications.

Formation of Deep Electron Traps by Yb3+ Codoping Leads to Super-Long Persistent Luminescence in Ce3+-Doped Yttrium Aluminum Gallium Garnet Phosphors.

The Y3Al2Ga3O12:Ce3+-Cr3+ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr3+ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr3+ and lanthanide ions, we selected Yb3+ as a deeper electron trapping center. The Y3Al2Ga3O12:Ce3+-Yb3+ phosphors show Ce3+:5d → 4f green persistent luminescence after blue light excitation. The formation of Yb2+ was confirmed by the increased intensity of absorption due to Yb2+:4f-5d at 585 nm during the charging process. This result indicates that the Yb3+ ions act as electron traps by capturing an electron. From the thermoluminescence glow curves, it was found that the Yb3+ trap makes a much deeper electron trap with a 1.01 eV depth than the Cr3+ electron trap with a 0.81 eV depth. This deeper Yb3+ trap provides a much slower detrapping rate of filled electron traps than the Cr3+-codoped persistent phosphor. In addition, by preparing transparent ceramics and optimizing Ce3+ and Yb3+ concentrations, the Y3Al2Ga3O12:Ce3+(0.2%)-Yb3+(0.1%) as-made transparent ceramic phosphor showed super-long persistent luminescence for over 138.8 h after blue light charging.

Near-infrared rechargeable “optical battery” implant for irradiation-free photodynamic therapy

As a minimal or noninvasive therapeutic method for tumors, photodynamic therapy (PDT) induced by the external laser irradiations has attracted great attentions. However, the UV–visible responsive property with low tissue penetration and photothermal effect from the prolonged irradiation impedes their further applications. Herein, a near-infrared (NIR) rechargeable “optical battery” for irradiation-free PDT is fabricated by embedding upconversion materials, persistent luminescence materials, photosensitizer into biocompatible polydimethylsiloxane. After 5 s quickly charged by 980-nm NIR laser, the PDT “optical battery” can generate green persistent luminescence and produce cytotoxic singlet oxygen for continuous irradiation-free PDT (∼30 min) without external irradiation. Due to deep tissue penetration and discontinuous short exposure of NIR light charging source, the “optical battery” can still be charged to continuously generate singlet oxygen in deep tissue (∼4 mm) with low photothermal effect. The PDT implant can be easily optimized in size and shape aiming at different nidus sites and achieved different functions by adding other functional components (e.g. CaO2 for oxygen envolving to overcome hypoxia tumor). The effective tumor proliferation inhibiting capability of this NIR rechargeable “optical battery” may give rise to next generation of intelligent stimuli-responsive nanomedicine and noninvasive photo bio-stimulation research for future clinical applications.

Origin of the green persistent luminescence of Eu-doped SrAl2O4from a multiconfigurationalab initiostudy of 4f7→ 4f65d1transitions

The green persistent luminescence from SrAl2O4:Eu is assigned to Eu2+at the Sr2 site based on a multiconfigurationalab initiostudy.

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.

Structural, persistent luminescence properties and trap characteristics of an orthosilicate phosphor: LiGaSiO4:Mn2+

A novel orthosilicate persistent phosphor LiGaSiO4:Mn2+ has been developed by solid state reaction method. The refined crystal structure of the LiGaSiO4 is solved. The photoluminescence and persistent spectra, decay curve and thermoluminescence have been investigated in details. It reveals that the Mn2+ at Li+ sites in the LiO4 tetrahedron are able to show intense green persistent luminescence, which can be measured for approximately 6 h and 2.1 h (0.32 mcd/m2) after exposure to ultraviolet and artificial sunlight irradiation. The trap distribution of phosphor is studied by using a series of excitation temperature dependent thermoluminescence experiments based on initial rising method. The different roles of the shallow and deep traps on the persistent luminescence have been revealed by the thermoluminescence fading experiments.

On thermoluminescence of Lu2O3:Tb,Ta ceramic storage phosphors

For the first time thermoluminescence of Lu2O3:Tb,Ta ceramics sintered at 1700°C in different atmospheres – air, forming gas and vacuum – were investigated. Exposure of the materials into the 254nm radiation of a mercury lamp led to the Tb3+ green persistent luminescence of noticeable intensity. Thermoluminescence glow curves revealed two strong thermoluminescence peaks located around 170°C and 250°C, with the former being by a factor of ~2–2.5 more intense compared to the latter. Tmax-Tstop thermoluminescence experiments revealed that each of these bands is composed of numerous individual, strongly overlapping components of similar characteristics, known as continuous traps distribution. The highest thermoluminescence was observed from the material sintered in vacuum. Those sintered in air or forming gas showed the storage capabilities by about 15–25% lower, though shapes of their glow curves were very similar. A scheme of carriers trapping was proposed with the hole immobilized at Tb3+ site and the electron being trapped in the vicinity Ta(V) impurity due to its strong positive net charge in the Lu site.

Study on Trap Levels in SrSi2AlO2N3:Eu2+,Ln3+ Persistent Phosphors Based on Host-Referred Binding Energy Scheme and Thermoluminescence Analysis.

We investigated the effect of trivalent lanthanide substitution on a novel oxynitride persistent phosphor SrSi2AlO2N3:Eu2+,Ln3+, which shows green persistent luminescence for more than 2 h. First, an energy level diagram by using the host-referred binding energy (HRBE) scheme was constructed. The location of the energy levels of all divalent and trivalent lanthanides referred to the energy band of the host SrSi2AlO2N3 was estimated. Then, thermoluminescence (TL) measurements in the target persistent phosphors were performed to obtain direct experimental results on the trap depth. We found that the trap levels based on the TL measurements coincided well with the 4f ground states of divalent lanthanide codopants in SrSi2AlO2N3:Eu2+,Ln3+. The result strongly suggests the effective traps for persistent luminescence in SrSi2AlO2N3:Eu2+,Ln3+ could be due to the aliovalent substitution of Ln3+ for Sr2+, which can be controlled by selecting suitable codopant Ln3+. The work shows the HRBE scheme may offer a way to understand the nature of defects in the persistent phosphor as well as a possible guideline to design new persistent phosphors with required trap depths.