Afterglow-Suppressed Lu2O3:Eu3+ Nanoscintillators for High-Resolution and Dynamic Digital Radiographic Imaging.

Lu2(1-x)Eu2xO3 nanoscintillators (x = 0.005, 0.01, 0.03, 0.05, 0.07, and 0.10) with red emission were synthesized by a coprecipitation method. It is found that their photo- and radioluminescence intensities increase with increasing Eu3+ concentration until x = 0.05. According to their concentration-dependent luminescence intensity ratios (I610(C2)/I582(S6)), the existing energy transfer from Eu3+(S6) (occupying S6 sites) to Eu3+(C2) (occupying C2 sites) can be confirmed. Based on the spectral data and density functional theory (DFT) calculations, the origin of Lu2O3:Eu3+ persistent luminescence at low concentration might be related to the tunneling processes between Eu3+ (occupying C2 and S6 sites) and oxygen interstitials (Oi×). After dispersing afterglow-suppressed Lu2O3:Eu3+ nanoscintillators into polymethyl methacrylate (PMMA) polymer-acetone solution, flexible PMMA-Lu2O3:Eu3+ composite films with high thermal stability and radiation resistance were fabricated by a doctor blade method. As the flexible composite film was used as an imaging plate, static X-ray images with high spatial resolution (5.5 lp/mm) under an extremely low dose of ∼1.1 µGyair can be acquired. When a watch with a moving second hand was used as an object, the dynamic X-ray imaging can be realized under a dose rate of 55 µGyair·s-1. Our results demonstrate that Lu2O3:Eu3+ nanoscintillators can be regarded as candidate materials for dynamic digital radiographic imaging.

Photothermal conversion performance and acid-induced aggregation of PLNP-Bi2S3 composite nanoplatforms.

Poly(sodium 4-styrenesulfonate) (PSS) molecule modified PLNP-Bi2S3 composite nanoplatforms were constructed by using polyvinylpyrrolidone (PVP) modified Bi2S3 nanoparticles (∼4.6 nm) as a photothermal agent and hexadecyl trimethyl ammonium bromide (CTAB) coated Zn2Ga2.98Ge0.75O8:Cr0.023+ (ZGGO:Cr3+@CTAB) persistent luminescence nanoparticles (PLNPs) through electrostatic adsorption. It is found that the above composite nanoplatforms have excellent laser-irradiation thermal stability and good photothermal conversion performance. The measured photothermal conversion efficiency is ∼44%, which is higher than that (∼37%) of the PLNP-GNR (gold nanorod) composite nanoplatforms. Meanwhile, PSS modified PLNP-Bi2S3 composite nanoplatforms exhibited good solution dispersibility in blood and normal tissue environments. While reaching tumor sites, the above composite nanoplatforms can be rapidly accumulated in cancer cells with acidic environments. This pH-responsive acid-induced aggregation can be ascribed to the chemical reaction induced by the protonation of PSS modified PLNP-Bi2S3 composite nanoplatforms with a negatively charged surface in the acidic environments. Our results suggest that PSS modified PLNP-Bi2S3 composite nanoplatforms might be applied to precision diagnosis and therapy of deep-tissue tumors.

X-ray/red-light excited ZGGO:Cr,Nd nanoprobes for NIR-I/II afterglow imaging.

Zn2Ga3-x-yCrxNdyGe0.75O8 (ZGGO:Crx,Ndy) persistent luminescent nanoparticles (PLNPs) (x = 0, 0.02; and y = 0, 0.01, 0.02, 0.03, 0.04) were synthesized via a hydrothermal method in combination with a following heat treatment under vacuum. The effects of Nd3+ concentration on chemical composition, size distribution, luminescence property, the persistent energy transfer from Cr3+ to Nd3+ and afterglow imaging were studied in detail. When the Nd3+ concentration was increased from 0 to 0.04, the particle size increased from 45.4 to 86.2 nm. The afterglow emissions in the NIR-I (696 nm) and NIR-II (1067 nm) regions, which are ascribed to the 2E, 4T2→4A2 transitions of Cr3+ and the 4F3/2→4I11/2 transition of Nd3+, respectively, were simultaneously acquired after stopping the 635 nm excitation. Among the nanoparticles with different concentrations, ZGGO:Cr0.02,Nd0.02 exhibits the strongest NIR-II afterglow intensity and the corresponding energy transfer efficiency from Cr3+ to Nd3+ is found to be 25.9%. In addition, enhanced X-ray excited afterglow imaging can be observed in Nd3+/Cr3+ codoped nanoparticles dispersed in water, human serum albumin solution and simulated lysosomal environment compared to the Cr3+ singly doped nanoparticles. Renewable NIR afterglow imaging was realized through an X-ray reexcitation strategy. In particular, both the X-ray excitation strategy accompanied by NIR-I afterglow emission and the red light (635 nm) excitation strategy accompanied by NIR-II afterglow emission exhibit high tissue penetration capability. This study provides a further understanding of how to develop a suitable strategy for realizing deep tissue autofluorescence-free bioimaging.

Enhancing photoluminescence of carbon quantum dots doped PVA films with randomly dispersed silica microspheres.

As a kind of excellent photoluminescent material, carbon quantum dots have been extensively studied in many fields, including biomedical applications and optoelectronic devices. They have been dispersed in polymer matrices to form luminescent films which can be used in LEDs, displays, sensors, etc. Owing to the total internal reflection at the flat polymer/air interfaces, a significant portion of the emitted light are trapped and dissipated. In this paper, we fabricate free standing flexible PVA films with photoluminescent carbon quantum dots embedded in them. We disperse silica microspheres at the film surfaces to couple out the total internal reflection. The effects of sphere densities and diameters on the enhancement of photoluminescence are experimentally investigated with a homemade microscope. The enhancement of fluorescence intensity is as high as 1.83 when the film is fully covered by spheres of 0.86 [Formula: see text]m diameter. It is worth noting that the light extraction originates from rather the scattering of individual spheres than the diffraction of ordered arrays. The mechanism of scattering is confirmed by numerical simulations. The simulated results show that the evanescent wave at the flat PVA/air interface can be effectively scattered out of the film.

Enhanced near infrared persistent luminescence of Zn2Ga2.98Ge0.75O8:Cr0.02 3+ nanoparticles by partial substitution of Ge4+ by Sn4.

Spinel-phase Zn2Ga2.98Ge0.75-x Sn x O8:Cr0.02 3+ (ZGGSO:Cr3+) nanoparticles with various Sn4+ concentrations were prepared by a hydrothermal method in combination with a post-annealing in vacuum at high temperature. For these nanoparticles, the observed near infrared (NIR) persistent luminescence peaked at ∼697 nm and originates from the 2E, 4T2 (4F) → 4A2 transitions of Cr3+ and the afterglow time exceeds 800 min. For both the interior and surface Cr3+ ions in the ZGGSO host, it can be found that the increased energy transfer from Cr3+ to the deep trap (anti-site defects, ) after the substitution of Ge4+ by Sn4+ plays a key role in enhancing the persistent luminescence of the ZGGSO:Cr3+ nanoparticles. Strikingly, this energy transfer process can be controlled through the variations in the crystal field strength and the trap depths. Our results suggest that not only Sn4+ substitution can improve in vivo bioimaging but also the existence of deep traps in ZGGSO:Cr3+ nanoparticles is helpful for retracing in vivo bioimaging at any time.

A Pr3+ doping strategy for simultaneously optimizing the size and near infrared persistent luminescence of ZGGO:Cr3+ nanoparticles for potential bio-imaging.

Spinel-phase Zn2Ga2.98-xGe0.75O8:Cr0.020,Prx (ZGGO:Cr3+,Pr3+) near infrared (NIR) persistent luminescence nanoparticles (PLNPs) with different amounts of Pr3+ dopant were prepared by a hydrothermal method in combination with a subsequent annealing in a vacuum. For these nanoparticles, the averaged particle size decreases from 64 to 37 nm with increasing Pr3+ doping concentration from 0 to 0.025 and Cr3+ and Pr3+ ions are uniformly doped into the interior and surface of a single nanoparticle. It can be found that Pr3+ doping leads to the appearance of more anti-site pairs () around distorted octahedral Cr3+ ions and enhanced NIR emissions around 697 nm, which originate from the 2E(2G) → 4A2(4F) and 4T2(4F) → 4A2(4F) transitions of the interior and surface Cr3+ ions in the nanoparticles. In particular, for the interior Cr3+ ions in the Pr3+ doped nanoparticles, the enhanced NIR luminescence can be attributed to the suppressed energy transfer of the excited electrons from the 4T2(4F) level to the trap level related to anti-site pairs () around the distorted octahedral Cr3+ ions. Our results suggest that Pr3+ doped ZGGO:Cr3+ PLNPs have potential applications for bio-imaging.

Enhanced emission of encaged-OH--free Ca12(1-x)Sr12xAl14O33:0.1%Gd3+ conductive phosphors via tuning the encaged-electron concentration for low-voltage FEDs.

Encaged-OH--free Ca12(1-x)Sr12xAl14O33:0.1%Gd3+ conductive phosphors were prepared through a melt-solidification process in combination with a subsequent heat treatment. Absorption spectra showed that the maximum encaged-electron concentration was increased to 1.08 × 1021 cm-3 through optimizing the doping amount of Sr2+ (x = 0.005). Meanwhile, FTIR and Raman spectra indicated that pure Ca11.94Sr0.06Al14O33:0.1%Gd3+ conductive phosphor without encaged OH- and C22- anions was acquired. For the conductive powders heat-treated in air for different times, the encaged-electron concentrations were tuned from 1.02 × 1021 to 8.3 × 1020 cm-3. ESR, photoluminescence, and luminescence kinetics analyses indicated that the emission at 312 nm mainly originated from Gd3+ ions surrounded by encaged O2- anions, while Gd3+ ions surrounded by encaged electrons had a negative contribution to the UV emission due to the existence of an energy transfer process. Under low-voltage electron-beam excitation (3 kV), enhanced cathodoluminescence (CL) of the conductive phosphors could be achieved by tuning the encaged-electron concentrations. In particular, for the encaged-OH--free conductive phosphor, the emission intensity of the CL was about one order of magnitude higher than that of the conductive phosphor containing encaged OH- anions. Our results suggested that the encaged-OH--free conductive phosphors have potential application in low-voltage FEDs.

Enhancement of encaged electron concentration by Sr(2+) doping and improvement of Gd(3+) emission through controlling encaged anions in conductive C12A7 phosphors.

Conductive C12A7:0.1%Gd(3+),y%Sr(2+) powders with different Sr(2+) doping concentrations have been prepared in a H2 atmosphere by a solid state method in combination with subsequent UV-irradiation. The encaged electron concentration could be modulated through tuning Sr(2+) doping and its maximum value reaches 2.3 × 10(19) cm(-3). This is attributed to the competition between enhanced uptake and the release of the encaged anions during their formation and diffusion processes and the suppression of encaged electrons generation due to the increased encaged OH(-) anions and the decreased encaged O(2-) anions. Although there exists encaged electrons and different encaged anions (O(2-), H(-) and OH(-)) in C12A7 conductive powders prepared through the hydrogen route, a dominant local environment around Gd(3+) could be observed using electron spin resonance (ESR) detection. It can be ascribed to the stronger coupling of the encaged OH(-) to the framework of C12A7 than those of the encaged electrons, O(2-) and H(-) anions. In addition, emission of Gd(3+) ions is enhanced under UV or low voltage electron beam excitation and a new local environment around Gd(3+) ions appears through the thermal annealing in air because of the decrease of the encaged OH(-) anions and the increase of the encaged O(2-) anions. Our results suggested that Sr(2+) doping in combination with thermal annealing in air is an effective strategy for increasing the conductive performance and enhancing the emission of rare earth ions doped into C12A7 conductive phosphors for low-voltage field emission displays (FEDs).

A vacuum-annealing strategy for improving near-infrared super long persistent luminescence in Cr(3+) doped zinc gallogermanate nanoparticles for bio-imaging.

Novel Cr(3+) doped zinc gallogermanate (ZGGO) nanoparticles with 697 nm near-infrared (NIR) super long afterglow were prepared via a hydrothermal method. Subsequently, a vacuum-annealing strategy was adopted to improve NIR afterglow in ZGGO:Cr(3+) nanoparticles. For the sample annealed at 800 °C, no variation in the particle size is observed, the persistent luminescence increases by an order of magnitude (∼14 times) and the NIR afterglow time reaches more than 15 hours relative to the as-prepared sample. After annealing at temperatures higher than 880 °C, the persistent luminescence of the nanoparticles is enhanced, but they show aggregated-surface behavior. Meanwhile, shallow and deep traps are generated, related to the antisite defects and VGe-Cr(3+)-VO defect clusters, respectively. Finally, we apply ZGGO:Cr(3+) persistent luminescence nanoparticles (PLNPs) to a human serum albumin (HSA) colloid solution, and more than 1 h of NIR persistent luminescence is detected under 320 nm excitation. The quenching effect of NIR luminescence by OH(-) in the HSA solution is observed based on the reduced contribution of surface Cr(3+) in PLNPs to NIR luminescence. Our results suggest that ZGGO:Cr(3+) PLNPs have potential applications for in vivo bio-imaging.

A multiphase strategy for realizing green cathodoluminescence in 12CaO·7Al2O3-CaCeAl3O7:Ce3+,Tb3+ conductive phosphor.

A multiphase strategy is proposed and successfully applied to make the insulating green phosphor CaCeAl3O7:Tb(3+) conductive in the form of 12CaO·7Al2O3-CaCeAl3O7:Ce(3+),Tb(3+). The phosphor shows bright green-light emission with a short lifetime (2.51 ms) under low-voltage electron beam excitation (3 kV). The green photo- and cathodoluminescence from (5)D4-(7)F(J) (J = 6, 5, 4, 3) transitions of Tb(3+) are significantly enhanced in comparison with pure C12A7:Tb(3+). It was confirmed that this enhancement is the consequence of the joint effects of energy transfer from Ce(3+) to Tb(3+) and broadening of the absorption spectrum of Ce(3+) due to the existence of multiple phases. In particular, under 800 V electron beam excitation, cathodoluminescence is improved by the modified electrical conductivity of the phosphor. When compared to the commercial Zn2SiO4:Mn(2+) with a long luminescence lifetime of 11.9 ms, this conductive green phosphor has greater advantage for fast displays.

White luminescence of Dy3+ ions doped 12CaO 7Al2O3 nanopowders under UV light excitation.

12CaO 7Al2O3:Dy3+ nanopowders were successfully synthesized by the chemical co-precipitation method. X-ray diffraction result shows that the single 12CaO 7Al2O3 phase is formed with Dy3+ ions to replace the Ca2+ ions in the host of 12CaO 7Al2O3. The yellow and blue emissions, attributed to the forced electric dipole transition of 4F(9/2) --> 6H(13/2) centered at 571 nm and the magnetic dipole transition of 4F(9/2) --> 6H(15/2) centered at 480 nm, respectively, were observed. The integrated intensity ratios of yellow to blue increase from 1.63 to 1.70 with Dy3+ concentration increasing from 0.8 to 2.0% for the as-prepared 12CaO 7Al2O3:xDy3+ phosphor. The significantly enhanced emission intensities of 12CaO 7Al2O3:1.0% Dy3+ phosphor annealed at 900 degrees C for 2 hours in vacuum ambient could be ascribed to the decrease of OH(-) groups and the change of the surface topography. The thermal stability and the Commission International de l'Eclairage coordinates were also investigated. All the photoluminescence characteristics indicate that Dy3+ ions doped 12CaO 7Al2O3 may be a good candidate for the solid state lighting phosphor as well as white light-emitting diodes.