The Down-Shifting (DS) of UV photons into the visible range has been attracting much attention for lighting appliances and solar cells. This work reported the DS luminescence in Ce3+-Tb3+ co-doped ...phosphate glasses. Photoluminescence and decay curves were measured and analysed. According to the emission spectra, it was noticed a decrease in emission of the Ce3+ peak intensity and an increase of the Tb3+ visible emission intensity when the Tb3+ concentration is enlarged, indicating an energy transfer process from Ce3+ to Tb3+. Moreover, it was observed that the blue emission of Tb3+ decreases, while the green emission enhances by gradually increasing Tb3+ concentration. According to the decay curves of Tb3+, this result can be explained by cross-relaxation between Tb3+ ions. The experimental temporal evolution of the green emission of Tb3+ ions obtained under excitation of the Ce3+ ions at 280 nm is well simulated using a proposed model. In this way, the dynamics of the processes involved is perfectly understood and can be applied for solar cell applications. Therefore, the samples were placed over a solar cell and excited with UV excitation. In this excitation range, the silicon solar cell is not efficient, but the Ce3+ ions absorb this energy and transfer to the Tb3+ ions, which produce an intense visible emission. This emission is detected by the solar cell and produces photocurrent. In summary, the use of co-doped phosphate glass could enhance the current in a solar cell in the UV region.
•The successful preparation of 0.5Ce3+–xTb3+ co-doped phosphate glasses for investigating downshifting to Tb3+ ions.•Confirmation of energy transfer from Ce3+ to Tb3+ ions, supported by decay curve analysis.•Observed photoluminescence intensity increases with Tb3+ concentration and decreases with Ce3+.•Photocurrent generation at 280 nm excitation with co-doped glass, indicating potential for UV region current enhancement.
Er:YAP crystals have been proved promising mid-infrared gain materials but there is few systematic study focused on the relationship between the doping concentration and spectral properties. In this ...work, Er:YAP crystals with a series of doping concentrations(0.1 at.%, 1 at.%, 5 at.%, 10 at.%, 15 at.%, 30 at.%) were fast grown successfully by a modified laser-heated pedestal growth (LHPG) method. Through investigating doping concentration dependent spectral characteristics in detail, we found that the cross relaxation process (Er3+: 4S3/2+4I15/2 → 4I9/2+4I13/2) gets significantly enhanced with the doping concentration when it is below 5 at.%, and eventually tends to saturate. And the cooperative up-conversion process (Er3+: 4I13/2+4I13/2 → 4I15/2+4I9/2) conducive to high-efficiency ∼3 μm laser starts to dominate when the doping concentration is 5 at.% or even less. This result demonstrates the potential of Er:YAP crystals to achieve high-power and high-efficiency laser output under relatively low Er-doping concentration, and offers a valuable guidance for doping optimization of Er:YAP systems.
•Er:YAP is promising to achieve high output power in near 3 μm region.•Er:YAP crystals were rapidly synthesized by a modified laser-heated pedestal growth (LHPG) method.•Spectroscopic measurements, fluorescence kinetic and energy transfer mechanism were investigated.•The CU2 process, which is conducive to Er ∼3 μm laser turn to be dominant at around 5 at.% doping concentration.
Statins are drugs that specifically inhibit the enzyme HMG-CoA reductase and thereby reduce the concentration of low-density lipoprotein cholesterol, which represents a well-established risk factor ...for the development of atherosclerosis. The results of several clinical trials have shown that there are important intermolecular differences responsible for the broader pharmacologic actions of statins, even beyond HMG-CoA reductase inhibition. According to one hypothesis, the biological effects exerted by these compounds depend on their localization in the cellular membrane. The aim of the current work was to study the interactions of different statins with phospholipid membranes and to investigate their influence on the membrane structure and dynamics using various solid-state NMR techniques. Using 1H NOESY MAS NMR, it was shown that atorvastatin, cerivastatin, fluvastatin, rosuvastatin, and some percentage of pravastatin intercalate the lipid-water interface of POPC membranes to different degrees. Based on cross-relaxation rates, the different average distribution of the individual statins in the bilayer was determined quantitatively. Investigation of the influence of the investigated statins on membrane structure revealed that lovastatin had the least effect on lipid packing and chain order, pravastatin significantly lowered lipid chain order, while the other statins slightly decreased lipid chain order parameters mostly in the middle segments of the phospholipid chains.
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•Different statins bind and influence lipid membranes differently.•Different average locations of the in the bilayer were observed.•The data should contribute to better understanding pharmacological differences.
Abstract
Fluorescence bioimaging based on rare-earth-doped nanocrystals (RENCs) in the shortwave infrared (SWIR, 1000–3000 nm) region has aroused intense interest due to deeper penetration depth and ...clarity. However, their downshifting emission rarely shows sufficient brightness beyond 1600 nm, especially in NIR-IIc. Here, we present a class of thulium (Tm) self-sensitized RENC fluorescence probes that exhibit bright downshifting luminescence at 1600–2100 nm (NIR-IIb/c) for in vivo bioimaging. An inert shell coating minimizes surface quenching and combines strong cross-relaxation, allowing LiTmF
4
@LiYF
4
NPs to emit these intense downshifting emissions by absorbing NIR photons at 800 nm (large Stokes shift ~1000 nm with a absolute quantum yield of ~14.16%) or 1208 nm (NIR-II
in
and NIR-II
out
). Furthermore, doping with Er
3+
for energy trapping achieves four-wavelength NIR irradiation and bright NIR-IIb/c emission. Our results show that Tm-based NPs, as NIR-IIb/c nanoprobes with high signal-to-background ratio and clarity, open new opportunities for future applications and translation into diverse fields.
Highly doped lanthanide luminescent nanoparticles exhibit unique optical properties, providing exciting opportunities for many ground-breaking applications, such as super-resolution microscopy, ...deep-tissue bioimaging, confidentiality, and anticounterfeiting. However, the concentration-quenching effect compromises their luminescence efficiency/brightness, hindering their wide range of applications. Herein, we developed a low-temperature suppression cross-relaxation strategy, which drastically enhanced upconversion luminescence (up to 2150-fold of green emission) in Er3+-rich nanosystems. The cryogenic field opens the energy transport channel of Er3+ multiphoton upconversion by further suppressing phonon-assisted cross-relaxation. Our results provide direct evidence for understanding the energy loss mechanism of photon upconversion, deepening a fundamental understanding of the upconversion process in highly doped nanosystems. Furthermore, it also suggests the potential applications of upconversion nanoparticles for extreme ambient-temperature detection and anticounterfeiting.
This paper reports the effect of manganese incorporation on the structural, optical and luminescence properties of the as-deposited ZnS films prepared by RF magnetron sputtering process. Mn act as a ...nucleation centre for the growth of highly crystalline defect free ZnS films with mixed cubic and hexagonal phases. The +2 valence state of Mn ions in ZnS lattice is confirmed by the XPS analysis. An absorption band due to d-d transition of Mn2+ ions is visible in the absorption spectra of ZnS film with highest Mn doping concentration. ZnS:Mn films present an intense orange emission along with the host emissions of ZnS. Optimum Mn content for superior orange emission from ZnS:Mn films is found to be 3 wt %. Origin of orange photoluminescence emission due to the incorporation of Mn2+ in Zn2+ host lattice and its quenching due to cross-relaxation mechanism in the films with higher Mn doping concentration is discussed in detail. We report the possibility of one-step generation of white light emission from the as-synthesized ZnS:Mn films by the adequate tailoring of ZnS host emissions in the blue and green regions (445 nm and 530 nm respectively) and Mn related emission in the orange region (585 nm) employing only one excitation wavelength by suitably tuning the Mn doping concentrations. PL decay of the orange emission is monitored to explore the luminescence mechanism and lifetime of the emission.
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•Highly crystalline ZnS:Mn films showing blue, green and orange emissions are prepared.•Quenching of orange emission is explained by cross-relaxation mechanism.•Kinetics of the orange emission is studied by TCSPC measurements.•Possibility of white light generation by tailoring the three visible emissions is proposed.
Some new type of strontium magnesium borate glass system doped with Dy3+ (various contents 0.1, 0.3, 0.5, 0.7 and 1.0 mol%) were produced using the conventional melt-quenching. Obtained glasses were ...thermally stable, highly transparent, and moisture resistant. As-prepared samples were characterized to determine their spectroscopic traits. The Judd-Ofelt (J-O) intensity Ωλ (λ = 2, 4, 6) and radiative parameters were calculated to validate the experimental results on the optical characteristics. The XRD pattern of the as-quenched samples verified their glassy nature, FESEM images showed uniform textures and EDX analyses detected the presence of appropriate constituents in the host matrix. Glass containing 0.7 mol% of Dy3+ revealed the optimum optical traits where the luminescence emission intensity was attenuated beyond this content. The optical gain for two intense emission transitions (4F9/2→6H15/2 and 4F9/2→6H13/2) was evaluated. The values of Ωλ (λ = 2, 4, 6) determined the ionic nature of the bonding and symmetry environment of the Dy―ligand matrix based on the viscosity and rigidity of the host glass. The 6H15/2→6F11/2 transition was hypersensitive. The ratio of the yellow to blue (Y/B) emission intensity less than unity indicated the lower degree of covalence between Dy3+ and O2− ions thereby makes these glasses effective for the near UV―LEDs. The higher values of the branching ratio (≥ 50 %) and stimulated emission cross-section enabled the proposed glass composition potential for the optical amplifiers and fibres fabrication. The resonant energy transfer and cross-relaxation processes in the Dy3+ were attributed to be responsible for the improved optical features.
Dynamic exchange of water has been shown to effectively trigger thermally responsive shape memory effect (SME) in shape memory polymer (SMP) at room temperature. However, the working mechanism of ...cross-relaxation effects which are generated simultaneously from two stimulus fields of water and temperature, has not been understood. In this study, a 'cross-relaxation effects' model was formulated for describing water-induced relaxation, thermomechanical behavior and strain recovery of amorphous SMPs. Based on Maxwell's principle, the 'cross-relaxation effects' model was firstly proposed to quantitatively separate the effect of dynamic exchange of water on the thermochemical SME in SMP. Then the water-induced relaxation and strain recovery have been simulated and predicted using this model. Finally, experimental data were used to verify the proposed model, and the numerical results were found to fit well with the experimental ones. This 'cross-relaxation effects' model is expected to provide an effective tool for precise design and control of water-induced SME and shape memory behaviors by means of the dynamic exchange of water.
Luminescence thermometry is used in a variety of research fields for noninvasive temperature sensing. Lanthanide‐doped micro‐/nanocrystals are exceptionally suitable for this. The popular concept of ...luminescence‐intensity‐ratio thermometry is based on emission from thermally coupled levels in a single lanthanide ion, following Boltzmann's law. These thermometers can measure temperature with low uncertainty, but only in a limited temperature range. In this work, a Ho3+‐based thermometer is presented and quantitatively modeled with sustained low temperature uncertainty from room temperature up to 873 K. The thermometer shows bright green and red luminescence with a strong and opposite dependence on temperature and Ho3+ concentration. This is the result of temperature‐dependent competition between multi‐phonon relaxation and energy transfer, feeding the green‐ and red‐emitting levels, respectively, following excitation with blue light. This simple and quantitative model of this competition predicts the output spectrum over a wide range of temperatures (300–873 K) and Ho3+ concentrations (0.1–30%). The optimum Ho3+ concentration can thus be determined for reliable measurements over any temperature range of interest. Quantitative modeling as presented here is crucial to optimally benefit from the potential of energy‐transfer thermometers to achieve low measurement uncertainties over a wide temperature range.
The emission of Ho3+‐doped crystals can be used for remote thermometry. This work builds a quantitative model of how the emission color depends on temperature and Ho3+ doping concentration. The model demonstrates how tuning the Ho3+ doping concentration results in the most reliable temperature measurements.
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