| 1. |
- Bartholomew, John G., et al.
(författare)
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High-resolution spectroscopic techniques for studying rare-earth ions in nanoparticles
- 2023
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Rare-earth doped nanoparticles can exhibit narrow optical and spin linewidths at low temperatures. These outstanding properties for nanomaterials make them attractive for quantum technologies based on optically addressable spins such as quantum memories and computers. Although accurate linewidth measurements have been reported using, for example, spectral hole burning or photon echo techniques, so far they have been mostly restricted to large ensembles of particles. Being able to extend linewidths measurements to few and single particles is particularly important in view of their integration in nanophotonic devices. In this paper, we present techniques for determining inhomogeneous and homogeneous linewidths of small ensembles of rare-earth ions in doped nanoparticles with high signal-to-noise ratios for convenient integration times. Using these techniques we have observed property variations for particles from the same synthesis, a first step towards their optimization for applications in quantum technologies.
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| 2. |
- Binder, Christian, et al.
(författare)
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Phosphor thermometry for in-cylinder surface temperature measurements in diesel engines
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 226
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Tidskriftsartikel (refereegranskat)abstract
- Phosphor thermometry is a temperature measurement technique that has previously been employed in technically relevant applications to obtain surface temperature. The technique is based on temperature-dependent changes in a phosphor's luminescence. To improve the accuracy and precision of temperature measurements with this technique, the present study considers, by way of example, the impact of conditions inside the cylinder of a diesel engine on decay time based single-shot phosphor thermometry measurements. After an initial, general assessment of the effect of prevailing measurement conditions, this research investigates errors caused by soot luminosity, extinction, signal trapping and changes of phosphors' luminescence properties due to exposure to the harsh environment. Furthermore, preferable properties of phosphors which are suitable for in-cylinder temperature measurements are discussed. 16 phosphors are evaluated, including LaAlGe2O7:Tm, YVO4:(Dy,Ce), ZnS:(Tm,Ag), and ZnS:(Tm,Li) which – to the authors' knowledge – have previously not been used in thermometry. Results indicate that errors due to photocathode bleaching, extinction, signal trapping and changes of luminescence properties may cause an erroneous temperature evaluation with temperature errors in the order of several tens of Kelvin.
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| 3. |
- Feuk, Henrik, et al.
(författare)
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Laser excitation effects in lifetime-based high-speed phosphor thermometry
- 2022
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 250
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Tidskriftsartikel (refereegranskat)abstract
- With high-speed phosphor thermometry becoming more established follows the need for an improved understanding of laser excitation induced measurement errors. With this aim in mind, the impact of kHz laser excitation on the lifetime method was investigated for the phosphors Mg3FGeO6:Mn (MFG) and YVO4:Tm. The results showed that significant measurement errors can occur for both phosphors. The Maximum Entropy Method (MEM) was utilized to observe changes in the distribution of decay time with changes in laser excitation fluence and repetition rate. In the light of this analysis, it was concluded that the changes in measured decay time and therefore measured temperature cannot be primarily attributed to laser heating for either phosphor. The dominant source of changes in the measured decay time is ascribed to changes in the distributions of decay time with laser fluence for YVO4:Tm and laser irradiance for MFG.
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| 4. |
- Guo, Huijie, et al.
(författare)
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Regulation of photoinduced charge transfer in all-small-molecule organic solar cells through the synergistic effect of external electric field and solvent
- 2024
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Ingår i: Journal of Luminescence. - 0022-2313. ; 268
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Tidskriftsartikel (refereegranskat)abstract
- The donor (BTR-Cl) and acceptor (BTP-FCl-FCl) have well-defined small molecule properties and excellent repeatability, and they can form charge transfer complexes with a wide spectral absorption range. Using density functional theory (DFT), we simulate the photoinduced charge transfer of bulk-heterojunction (BHJ) organic solar cell (OSC) materials modulated by the external electric field (Fext) at the microscopic level. The excited-state properties, reorganization energy (λ), Gibbs free energy (ΔG), electron coupling matrix elements (VDA) and intermolecular charge transfer (ICT) rate dependent on Fext are systematically analyzed. The results manifest that Fext has apparent positive regulation on the charge separation rate (KCS), and VDA is the main factor affecting KCS. The synergistic effect of solvent and Fext on charge transfer process is further investigated. It is found that the charge transfer rate in solvent is lower than that in solvent-free conditions, and the charge transfer rate in chlorobenzene (CB) solvent does not change significantly under the control of Fext. At the same time, Fext has a positive effect on the charge transfer rate in tetrahydrofuran (THF) solvent. Considering the charge transfer rate under different solvents and Fext intensities, it is found that the solvent and Fext play an essential role in determining the KCS and charge recombination rate (KCR).
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| 5. |
- Khanin, Vasilii, et al.
(författare)
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Exciton interaction with Ce3+ and Ce4+ ions in (LuGd)3(Ga,Al)5O12 ceramics
- 2021
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- Scintillators based on Ce-doped garnets are regularly co-doped with Mg2+ or Ca2+ to form Ce ions in 4+ state and reduce undesired afterglow. However overly high Ce4+ concentration leads to poor light yield performance. In order to understand the reason for variation in luminescence efficiency of Ce3+- and Ce4+-doped garnets we investigate the differences in energy conversion processes in complex LuGd2Ga3Al2O12:Ce3+/Ce4+ ceramics by means of VUV synchrotron irradiation. At first we have established via transmission spectroscopy and X-ray absorption spectroscopy that LuGd2Ga3Al2O12:Ce, Mg sample contains cerium in the 4+ state only. Then we show with VUV spectroscopy efficient interaction of excitons with Gd3+ and Ce3+, and lack of exciton absorption edge in LuGd2Ga3Al2O12:Ce4+ excitation spectrum. Instead, Ce4+ exhibits charge-transfer absorption band in the range of exciton emission. We suggest that when Ce4+ concentration becomes too high, the exciton → Gd3+ → Ce3+ energy transfer path is hindered. It leads to high intensity of Gd3+ luminescence in Lu1Gd2Ga3Al2O12:Ce, Mg ceramics, but lowered Ce3+ X-ray excited luminescence. Fine balance between 3+ and 4+ Ce concentrations is necessary to achieve the best performance of garnet scintillators.
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| 6. |
- Kiligaridis, Alexander, et al.
(författare)
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Excitation wavelength dependence of photoluminescence flickering in degraded MAPbI3 perovskite and its connection to lead iodide formation
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 222
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskite semiconductors often exhibit photoluminescence blinking and flickering when luminescence of individual small nano- or even microcrystals is monitored. The nature of these fluctuations is not well understood but must be related to the presence of metastable non-radiative recombination channels and efficient charge migration in these materials. Here we report on the excitation wavelength dependence of photoluminescence flickering effect in degraded methylammonium lead iodide (MAPbI3) thin films. While the luminescence intensity is temporary stable when excited in the blue region with wavelength shorter than 530 nm, excitation with red light (wavelength longer than 530 nm) results in luminescence flickering. It is hypothesised that the wavelength dependence reflects the excitation energy dependence of the photochemical mechanism that switches non-radiative recombination channels on and off. The effect can also be related to hindered charge carrier diffusion due to their localization in the interfacial layer between MAPbI3 and PbI2 which is formed in the course of degradation.
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| 7. |
- Labrador Paez, Lucia, et al.
(författare)
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Eu 3+luminescent ions detect water density anomaly
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- It is well known that water density varies anomalously with temperature. However, nowadays there is still a lack of agreement on the causes of this phenomenon. In this work, we use Eu3+ luminescent ion as a probe to investigate the changes in the arrangement of water molecules around the temperature of maximum density. The slight changes in the arrangement of water molecules in the first coordination sphere of Eu3+ ions due to the water density anomaly affect the variation with temperature of Eu3+ ions emission spectra and intensity decay time. This is the first time, to the best of our knowledge, that the effect of the anomaly in the density of water is detected by a luminescent material. From these experimental results we can infer that possibly the anomaly could be caused by variation in the length of hydrogen bonds between molecules with temperature for both water and heavy water.
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| 8. |
- Liu, Yong-feng, et al.
(författare)
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Sulfur quantum dot as a fluorescent nanoprobe for Fe3+ ions : Uncovering of detection mechanism, high sensitivity, and large detection range
- 2023
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Ingår i: Journal of Luminescence. - : Elsevier. - 0022-2313 .- 1872-7883. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Sulfur quantum dots (SQDs), as a novel metal-free fluorescent material, are getting increasingly tremendous attention in metal ion detection, especially for Fe3+, due to the merits of antimicrobial potential, low toxicity, and exciting optoelectronic properties. However, sensing mechanism of SQD based fluorescent probe for Fe3+ is not clear yet, and high sensitivity and large detection range remain a challenge. Here, we report the synthesis of hydrophilic SQDs as a fluorescent nanoprobe for Fe3+ via a fluorescent turn-off mode. We systematically studied the quenching mechanism by ultraviolet–visible absorption spectra, steady-state and time-resolved photoluminescent spectra, and temperature-dependent quenching constants. Results unclearly evidenced the quenching behavior to both inner filter effect and static quenching. Furthermore, the nanoprobe presents a large detection range from 2.5 to 700 μM and a limit of detection low to 53.6 nM, both of which are the record performance to our knowledge. At last, it shows high selectivity toward Fe3+ and presents no ionic strength effect in the range of investigation, which enables surprising results for Fe3+ detection in deionized water with interference ion and real water samples.
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| 9. |
- Markina, D. I., et al.
(författare)
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Photophysical properties of halide perovskite CsPb(Br1-xIx)3 thin films and nanowires
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 220
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Tidskriftsartikel (refereegranskat)abstract
- Thin films and nanowires based on lead halide perovskites are promising objects for the design of various optoelectronic devices as well as nano- and microlasers. One of the main advantages of such materials is their absorption and photoluminescence spectra tuning across the visible range via the change in their chemical composition, for instance, by substitution of one halide atom (Br) for another one (I) in the crystal lattice of CsPb(Br1-xIx)3. However, this approach gives materials showing unstable photoluminescence behavior caused by light-induced perovskite phase separation under high-intensity excitation at room temperature. In this work, CsPb(Br1-xIx)3 thin films and nanowires are obtained by chemical vapor anion exchange method from their CsPbBr3 counterparts fabricated by improved wet chemical methods. Spontaneous and stimulated emission from the mixed-halide and pristine bromide samples are studied. Tribromide nanowires exhibit lasing with relatively low thresholds (10–100 μJ/cm2) and high Q-factor of the laser mode up to 3500. The temperature dependence of the photoinitiated phase separation in CsPbBr1.5I1.5 samples is investigated, showing that light-induced phase instability of the mixed-halide nanowires can be suppressed at the somewhat higher temperature (250 K) than the value observed for the thin films having a similar chemical composition. The results obtained are important for the optimization of the functioning of optoelectronic devices based on considered perovskite materials.
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| 10. |
- Merdasa, Aboma, et al.
(författare)
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Microscopic insight into the reversibility of photodegradation in MAPbI3 thin films
- 2020
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Whether optoelectronic devices based on metal-halide perovskite semiconductors will become a commercially viable technology will be determined by their intrinsic and operational stability. Recent results indicate there is some reversibility of perovskite degradation in thin films and devices, although mechanistic insight into the processes driving degradation and recovery are still scarce. We here present a comparative spectroscopic study of methylammonium lead iodide (MAPbI3) films having undergone either photo- or thermal degradation under controlled conditions. We confirm that the degradation mechanism pertaining to each type of stress is inherently different. Our results from photoluminescence microscopy measurements paint a spatially, spectrally and temporarily resolved picture showing that, unlike thermally degraded samples, photodegraded samples are in a state that intermittently recovers to luminescent MAPbI3 upon laser excitation. This indicates that rather than irreversibly decomposing, photoinduced degradation leaves MAPbI3 structurally or compositionally intact but induces defects causing non-radiative recombination losses.
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