•An original color-tunable persistent luminescence phosphor LiTaO3:Pr3+ was synthesized via solid-state method.•The persistent luminescence emission of LiTaO3:Pr3+ can be modulated from pale yellow ...to deep orange-red merely by changing the concentration of Pr3+.•Dynamic QR code for anti-counterfeiting was developed.
In this work, an original color-tunable persistent luminescence (PersL) phosphor based on Pr3+ doped LiTaO3 (LTO) was realized. The PersL emission can be modulated from pale yellow to deep orange-red merely by changing the concentration of Pr3+, which attributed to the concentration quenching resulted from the cross-relaxation (CR) effect. Thermoluminescence (TL) analysis shows that the continuous shallow traps (0.668–0.8 eV) are suitable for PersL. Moreover, it also exhibits excellent photostimulated luminescence (PSL) performance owing to the presence of stable deep traps of 0.916 eV. A possible PersL mechanism of LTO:Pr3+ is put forward to explain this phenomenon. Finally, inspired by this multicolor PersL feature, a quick response code (QR-code) and an arrow pattern are developed, revealing that LTO:Pr3+ is an ideal material for dynamic anti-counterfeiting. Our work is designed to promote the practical applications of PersL materials in information security areas.
Cross‐relaxation among sensitizers is commonly regarded as deleterious in fluorescent materials, although favorable in photothermal agents. Herein, we coated Prussian blue (PB) on NaNdF4 ...nanoparticles to fabricate core–shell nanocomplexes with new cross relaxation pathways between the ladder‐like energy levels of Nd3+ ions and continuous energy band of PB. The photothermal conversion efficiency was improved exceptionally and the mechanism of the enhanced photothermal effect was investigated. In vivo photoacoustic imaging and photothermal therapy demonstrated the potential of the enhanced photothermal agents. Moreover, the concept of generating new cross‐relaxation pathways between different materials is proposed to contribute to the design of all kinds of enhanced photothermal agents.
A bolt from the blue: Prussian blue (PB) has been coated on NaNdF4 nanoparticles to fabricate core–shell nanocomplexes with new cross‐relaxation pathways between the ladder‐like energy levels of Nd3+ ions and the continuous energy band of PB. This approach results in a dramatic increase in the photothermal conversion efficiency. In vivo photoacoustic imaging and photothermal therapy demonstrated the potential of the nanocomplexes.
In this work, Yb, Ho, Gd3+/Gd3+, Ce3+: NaY(WO4)2 phosphors doped with various concentrations of Gd3+ and Ce3+ ions were prepared via high-temperature solid-state method. Under the excitation of ...980 nm near-infrared light, the doping of Gd3+ ions enhances the red and green emission of Yb, Ho: NaY(WO4)2, and on this basis, the Y3+ ion is replaced by Ce3+ ion doping, the red upconversion emission intensity was enhanced with Ce3+ concentration increasing. It was found that two efficient cross-relaxation processes between Ho3+ and Ce3+ ions had been employed to enhance red emission and suppress green emission. The possible upconversion mechanisms between Ho3+ and Ce3+ ions were investigated in detail. Yb3+, Ho3+, Gd3+, Ce3+ co-doped NaY(WO4)2 phosphors have broad application prospects in the fields of anti-counterfeiting and display, magnetic resonance imaging and optical temperature sensors.
•The Yb, Ho: NaYGd(WO4)2 phosphors shows intense green UC emission on excitation with 980 nm.•The luminous color is tuned from green to red by introducing Ce3+ ions.•The two CR processes of Ce3+ ions enhance the red emission of the sample.•This sample is suitable for anti-counterfeiting applications.
Photon upconversion in lanthanide-doped upconversion nanoparticles offers a wide variety of applications including deep-tissue biophotonics. However, the upconversion luminescence and efficiency, ...especially involving multiple photons, is still limited by the concentration quenching effect. Here, we demonstrate a multilayered core-shell-shell structure for lanthanide doped NaYF
, where Er
activators and Yb
sensitizers are spatially separated, which can enhance the multiphoton emission from Er
by 100-fold compared with the multiphoton emission from canonical core-shell nanocrystals. This difference is due to the excitation energy transfer at the interface between activator core and sensitizer shell being unexpectedly efficient, as revealed by the structural and temperature dependence of the multiphoton upconversion luminescence. Therefore, the concentration quenching is suppressed via alleviation of cross-relaxation between the activator and the sensitizer, resulting in a high quantum yield of up to 6.34% for this layered structure. These findings will enable versatile design of multiphoton upconverting nanoparticles overcoming the conventional limitation.
Avalanche phenomena use steeply nonlinear dynamics to generate disproportionately large responses from small perturbations, and are found in a multitude of events and materials
. Photon avalanching ...enables technologies such as optical phase-conjugate imaging
, infrared quantum counting
and efficient upconverted lasing
. However, the photon-avalanching mechanism underlying these optical applications has been observed only in bulk materials and aggregates
, limiting its utility and impact. Here we report the realization of photon avalanching at room temperature in single nanostructures-small, Tm
-doped upconverting nanocrystals-and demonstrate their use in super-resolution imaging in near-infrared spectral windows of maximal biological transparency. Avalanching nanoparticles (ANPs) can be pumped by continuous-wave lasers, and exhibit all of the defining features of photon avalanching, including clear excitation-power thresholds, exceptionally long rise time at threshold, and a dominant excited-state absorption that is more than 10,000 times larger than ground-state absorption. Beyond the avalanching threshold, ANP emission scales nonlinearly with the 26th power of the pump intensity, owing to induced positive optical feedback in each nanocrystal. This enables the experimental realization of photon-avalanche single-beam super-resolution imaging
with sub-70-nanometre spatial resolution, achieved by using only simple scanning confocal microscopy and without any computational analysis. Pairing their steep nonlinearity with existing super-resolution techniques and computational methods
, ANPs enable imaging with higher resolution and at excitation intensities about 100 times lower than other probes. The low photon-avalanching threshold and excellent photostability of ANPs also suggest their utility in a diverse array of applications, including sub-wavelength imaging
and optical and environmental sensing
.
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Two-dimensional NOE (nuclear Overhauser effect) NMR spectroscopy was employed to investigate the dynamic properties of water within lyotropic bicontinuous lipidic cubic phases (LCPs) ...formed by monoolein (MO). Experiments observed categorically different effective residence times of water molecules: (i) in proximity to the glycerol moiety of MO, and (ii) adjacent to the hydrophobic chain towards the hydrocarbon tail of MO, as evidenced by the opposite signs of intermolecular NOE cross peaks between protons of water and those of MO in 2D 1H–1H NOESY spectra. Spectroscopic data delineating the different effective residence times of water molecules within both the gyroid (QIIG) and diamond (QIID) phase groups corresponding to hydration levels of 35 and 40 wt%, respectively, are presented. Additionally, an increase in effective residence time of water molecules in proximity to the glycerol moiety of MO in LCPs was observed upon storage at ambient temperature and in the presence of an additive lipid, cholesterol. Atom-specific NOE build-up curves for protons of water and those of MO are also given. The results presented herein provide new insight into the physicochemical properties and behaviour of water in LCPs, and demonstrate an additional avenue for experimental study of water–lipid interactions and hydration dynamics in model membranes and nanomaterials using 2D NOE NMR spectroscopy.
Purpose
Nuclear Overhauser effect (NOE) is based on dipolar cross‐relaxation mechanism that enables the indirect detection of aliphatic protons via the water proton signal. This work focuses on ...determining the reproducibility of NOE magnetization transfer ratio (NOEMTR) and isolated or relayed NOE (rNOE) contributions to the NOE MRI of the healthy human brain at 7 Tesla (T).
Methods
We optimized the B1+$$ {\mathrm{B}}_1^{+} $$ amplitude and length of the saturation pulse by acquiring NOE images with different B1+$$ {\mathrm{B}}_1^{+} $$ values with multiple saturation lengths. Repeated NOE MRI measurements were made on five healthy volunteers by using optimized saturation pulse parameters including correction of B0 and B1+$$ {\mathrm{B}}_1^{+} $$ inhomogeneities. To isolate the individual contributions from z‐spectra, we have fit the NOE z‐spectra using multiple Lorentzians and calculated the total contribution from each pool contributing to the overall NOEMTR contrast.
Results
We found that a saturation amplitude of 0.72 μT and a length of 3 s provided the highest contrast. We found that the mean NOEMTR value in gray matter (GM) was 26%, and in white matter (WM) was 33.3% across the 3D slab of the brain. The mean rNOE contributions from GM and WM values were 8.9% and 9.6%, which were ∼10% of the corresponding total NOEMTR signal. The intersubject coefficient of variations (CoVs) of NOEMTR from GM and WM were 4.5% and 6.5%, respectively, whereas the CoVs of rNOE were 4.8% and 5.6%, respectively. The intrasubject CoVs of the NOEMTR range was 2.1%–4.2%, and rNOE range was 2.9%–10.5%.
Conclusion
This work has demonstrated an excellent reproducibility of both inter‐ and intrasubject NOEMTR and rNOE metrics in healthy human brains at 7 T.
Purpose
CEST MRI experiments of mobile macromolecules, for example, proteins, carbohydrates, and phospholipids, often show signals due to saturation transfer from aliphatic protons to water. ...Currently, the mechanism of this nuclear Overhauser effect (NOE)‐based transfer pathway is not completely understood and could be due either to NOEs directly to bound water or NOEs relayed intramolecularly via exchangeable protons. We used glycogen as a model system to investigate this saturation transfer pathway in sugar polymer solution.
Methods
To determine whether proton exchange affected saturation transfer, saturation spectra (Z‐spectra) were measured for glycogen solutions of different pH, D2O/H2O ratio, and glycogen particle size. A theoretical model was derived to analytically describe the NOE‐based signals in these spectra. Numerical simulations were performed to verify this theory, which was further tested by fitting experimental data for different exchange regimes.
Results
Signal intensities of aliphatic NOEs in Z‐spectra of glycogen in D2O solution were influenced by hydroxyl proton exchange rates, whereas those in H2O were not. This indicates that the primary transfer pathway is an exchange‐relayed NOE from these aliphatic protons to neighboring hydroxyl protons, followed by the exchange to water protons. Experimental data for glycogen solutions in D2O and H2O could be analyzed successfully using an analytical theory derived for such relayed NOE transfer, which was further validated using numerical simulations with the Bloch equations.
Conclusion
The predominant mechanism underlying aliphatic signals in Z‐spectra of mobile carbohydrate polymers is intramolecular relayed NOE transfer followed by proton exchange.
A spectroscopic evaluation of Sm3+ doped TeO2-GeO2-ZnO glasses (0.5, 1.0, 3.0 and 5.0%) was carried with aim to determinate the dominant process in the cross-relaxation mechanism at high and low ...concentrations of Sm3. A new experimental spectroscopic technique is proposed, based on the analysis of the time evolution of the 600 m emission, corresponding to the 4G5/2 → 6H7/2 transition, obtained under spatial and temporal simultaneous excitation at 355 nm and into the infrared (950, 1085 1236, 1380 nm). It was possible to determine that at low Sm3+ content the dominant channel for cross relaxation is 4G5/2 + 6H5/2 → 6F5/2 + 6F11/2 and at high concentrations are: 4G5/2 + 6H5/2 → 6F7/2 + 6F9/2, 4G5/2 + 6H5/2 → 6F9/2 + 6F7/2, 4G5/2 + 6H5/2 → 6F11/2 + 6F5/2, and the least contributor one being 4G5/2 + 6H5/2 → 6F5/2 + 6F11/2. It is reported the optical absorption and Raman spectroscopies, photoluminescence spectra and decay time profiles as a function of Sm3+ concentration. Emission spectra measurements indicated that concentration quenching is active in the samples, being 1.0 mol% the optimum concentration for luminescence of Sm3+ ions. The decay time of 4G5/2 level upon 403 nm excitation, at 0.5% of Sm3+, presents a decay curve single exponential, however, when the concentration increases, the time decay reduces and becomes non-exponential. The Inokuti-Hirayama model was used to infer that an electric dipole-dipole mechanism is the dominant interaction in the energy transfer process between Sm3+-Sm3+ ions.
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•Luminescence on TeO-GeO-ZnO glasses activated with Sm3+ under UV-IR simultaneous excitation.•Non-radiative resonant energy transfer between Sm3+ ions.•Determination of the dominant process in the cross-relaxation mechanism for cross-relaxation Sm3+.
The purpose of this paper is to present a new spectroscopic experimental technique to study the contributions of the different cross-relaxation mechanisms observed in Dy3+ doped TeO2-GeO2-ZnO ...glasses, based on the luminescence decay curves from 4F9/2 → 6H13/2 (at 573 nm) transition of Dy3+ ions under spatial and temporal simultaneous UV (6H15/2 → 6P7/2) and IR (6H15/2 → 6F3/2,6H15/2 → 6H7/2 and 6H15/2 → 6H9/2) excitations, for which the results are reported. The spectroscopic characterization was carried out through Raman, optical absorption, luminescence decay time profiles, and energy transfer as a function of Dy3+ ions content (0.5–5%). Emission spectra measurements indicated that concentration quenching is active in the samples. The lifetime decay of emission at 573 nm (4F9/2 level) was studied under excitation at 355 nm. At lower concentration of Dy3+, the temporal behavior of the emission at 573 nm is exponential, however, it becomes non-exponential as the concentration increases. The emission decay curves at 573 nm were fitted to Inokuti-Hirayama model and an energy transfer process dominated by an electric dipole-dipole interaction was deduced. A shortened lifetime was observed as the dysprosium ion content increased, which is attributed to non-radiative energy transfer between Dy3+ ions through the cross-relaxation mechanism. The analysis of the 4F9/2 → 6H13/2 (573 nm) emission decays, obtained under simultaneous excitation at 355 nm and at different infrared excitations 6H15/2 → 6F3/2 (905 nm), 6H15/2 → 6H7/2 (1100 nm) and 6H15/2 → 6H9/2 (1285 nm), allowed the determination of the dominant process in the cross-relaxation mechanism at high and low concentrations of Dy3+. It was possible to infer that in the glass with low concentration of Dy3+ the mechanism occurs predominantly by 4F9/2 + 6H15/2 → 6F11/2 + 6F3/2 channel, and for high concentration of Dy3+, the channels 4F 9/2 + 6H15/2 → 6F11/2 + 6F3/2, F9/2 + 6H15/2 → 6F5/2 + 6F9/2 +5H7/2, and 4F9/2 + 6H15/2 → 6F3/2 + 6F11/2 + 5H9/2 have a similar contribution to the Dy3+-Dy3+ resonant energy transfer.
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