Herein, we demonstrate the photoluminescence properties of Dy
3+
-activated YNbO
4
, LuNbO
4,
and mixed Y
x
Lu
1−
x
NbO
4
:Dy
3+
(
x
= 0.25, 0.5, 0.75) phosphors. For this purpose, five samples ...with a fixed Dy
3+
concentration (2 mol%) were prepared by the solid-state reaction method. X-ray diffraction measurements showed that all phosphors crystallize in a monoclinic fergusonite-beta-(Y) structure with a C2/c space group. Scanning electron microscopy clearly shows that samples are composed of dense, well-developed micron-sized, cube-shaped grains with rounded edges. The photoluminescent emission spectra feature Dy
3+
peaks at standard positions corresponding to transitions from the
4
F
9/2
excited emitting level to the
6
H
J
(
J
= 15/2; 13/2; 11/2 and 9/2) lower levels with two dominant emission bands placed in the blue (~ 479 nm, B) and yellow (~ 576 nm, Y) spectral region. It is observed that with Lu increase in the host lattice Y/B ratio decreases toward the desired ratio of unity to obtain white light. To evaluate the suitability of these phosphors for use in solid-state lighting, their photoluminescence emission was analyzed in detail by calculating CIE coordinates, correlated color temperature (CCT) and Delta u,v (DUV). It is shown that CIE chromaticity coordinates of all Dy
3+
-activated Y
x
Lu
1−
x
NbO
4
samples (
x
= 0, 0.25, 0.5, 0.75, and 1) fall into the white portion of the diagram and that with the increase of Lu in the host lattice color becomes whiter. CCT values for all samples are in the cooler 4000–4500 K range with positive DUVs indicating that color points are placed above the black body curve. The average lifetime of
4
F
9/2
level is calculated to be ~ 0.2 ms for all Dy
3+
-activated Y
x
Lu
1−x
NbO
4
samples, indicating that there is no influence of the Y-to-Lu ratio in the host niobate material on the luminescence kinetics.
This paper provides the detailed study of (nano)particle's size effect on structural and luminescent properties of LaPO4:Eu3+ synthesized by four different methods: high temperature solid-state, ...co-precipitation, reverse micelle and colloidal. These methods delivered monoclinic monazite-phase submicron particles (> 100nm), 4 × 20nm nanorods and 5nm spheres (depending on the annealing temperature), 2 × 15nm nanorods, and ultra-small spheres (2nm), respectively. The analysis of emission intensity dependence on Eu3+ concentration showed that quenching concentration increases with a decrease of the particle size. The critical distance for energy transfer between Eu3+ ions is found to be 18.2Å, and the dipole-dipole interaction is the dominant mechanism responsible for the concentration quenching of emission. With the increase in Eu3+ concentration, the unit-cell parameter slightly increases to accommodate larger Eu3+ ions at sites of smaller La3+ ions. Photoluminescent emission spectra presented four characteristic bands in the red spectral region: at 592nm (5D0→7F1), at 612nm (5D0→7F2), at 652nm (5D0→7F3) and at 684nm (5D0→7F4), while in small colloidal nanoparticles additional emission bands from host defects appear at shorter wavelengths. Intensities of f-f electronic transitions change with particles size due to small changes in symmetry around europium sites, while emission bandwidths increase with the reduction of particle size due to increased structural disorder. Judd-Ofelt analysis showed that internal quantum yield of Eu3+ emission is strongly influenced by particle's morphology.
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Temperature sensing from the photoluminescence of MgAl2O4:Cr3+ ceramic powder is systematically investigated. Material was prepared by self-propagating high temperature synthesis method. In this ...host, Cr3+ experiences the strong crystal field, so the overlapping emissions from 2E and 4T2 energy levels are observed. Emission and excitation spectra were recorded from 300 K to 540 K. The broad photoluminescence attributed to 4T2→4A2 emission gains in intensity with increase in temperature on account of 2E→4A2 emission intensity until 460 K when both emissions start quenching. The emissions were separated by deconvolution at each temperature and used for the luminescence intensity ratio temperature readout method. The obtained relative sensitivity exhibited high values in the physiological range, from 3.5 %K−1 at 300 K to 2.9 %K−1 at 330 K, above 2 %K−1 below 400 K and above 1 %K−1 between 400 K and 540 K.
The sensitivity of luminescence thermometry is enhanced at high temperatures when using a three-level luminescence intensity ratio approach with Dy3+- activated yttrium aluminum perovskite. This ...material was synthesized via the Pechini method, and the structure was verified using X-ray diffraction analysis. The average crystallite size was calculated to be around 46 nm. The morphology was examined using scanning electron microscopy, which showed agglomerates composed of densely packed, elongated spherical particles, the majority of which were 80–100 nm in size. The temperature-dependent photoluminescence emission spectra (ex = 353 nm, 300–850 K) included Dy3+ emissions in blue (458 nm), blue (483 nm), and violet (430 nm, T 600 K). Luminescence intensity ratio, the most utilized temperature readout method in luminescent thermometry, was used as the testing method: a) using the intensity ratio of Dy3+ ions and 4I15/2→6H15/2/4F9/2→6H15/2 transitions; and b) employing the third, higher energy 4G11/2 thermalized level, i.e., using the intensity ratio of 4G11/2→6H15/2/4F9/2→6H15/2 transitions, thereby showing the relative sensitivities of 0.41% K−1 and 0.86% K−1 at 600 K, respectively. This more than doubles the increase in sensitivity and therefore demonstrates the method’s usability at high temperatures, although the major limitation of the method is the chemical stability of the host material and the temperature at which the temperature quenching commences. Lastly, it must be noted that at 850 K, the emission intensities from the energetically higher levels were still increasing in YAP: Dy3+.
We report on overcoming the sensitivity limit of Boltzmann's thermometers by utilization of seven thermalized Dy3+ excited states in the Lu1.5Y1·5Al5O12 host. Emission spectra recorded from room ...temperature to 938 K show transitions originating from seven 4F9/2, 4I15/2, 4G11/2, 4I13/2, 4M21/2, 4K17/2, and 4F7/2 excited levels to the 6H15/2 ground state. We introduce the multi-cascade LIR (McLIR) by extending the conventional, two-thermalized level Boltzmann-type LIR to seven thermalized levels. This approach provides higher energy differences between thermalized levels which results in five times larger sensitivity than in the conventional LIR. Considering energy differences between Dy3+ excited states of 1043, 2464, 4331, and 5089 cm−1, the luminescence thermometry with McLIR provided 0.35, 0.84, 1.47, 1.73% K−1 relative sensitivities at 650 K, respectively, in four different LIR combinations. The validity of the McLIR method and the effectiveness of thermalizations between levels is confirmed with the good theoretical fit of experimental data.
•Multilevel-cascade luminescence intensity ratio method McLIR is introduced.•7 thermalized levels of Dy3+ were employed for luminescence thermometry.•5 cascades in McLIR were utilized for increasing sensitivity of Boltzmann thermometer.•McLIR was tested on novel phosphor, LuYAG, up to 938 K.•5x increased sensitivity is obtained compared to the conventional method.
The multiparametric luminescence thermometry with Dy3+, Cr3+ double activated yttrium aluminium garnet – YAG is demonstrated. Phospors were synthesized via Pechini method and their structure is ...confirmed by X-ray diffraction analysis. Mean crystallite size of powders was calculated to be ~22 nm. Morphology was investigated using scanning electron microscopy showing combination of dense, different size chunks constituted of spherical particles bellow 50 nm in size. Photoluminescence emission spectra of the Dy3+, Cr3+ double activated YAG consist of blue and yellow Dy3+ emissions and the broad, deep red Cr3+ emission. The decrease in the Dy3+ emission intensity with the increase in the Cr3+ content indicates the efficient energy transfer from Dy3+ to Cr3+ of ~90%. Temperature-dependant photoluminescence emission measurements are performed under 484 nm and 582 nm excitation in the steady-state domain and in the 175 K–650 K temperature range. The noted alterations of luminescence with temperature present an excellent base for studying the multiparametric temperature readouts. The luminescence intensity ratio, the most frequently exploited luminescent thermometry temperature readout method, was tested using: i) the combination of Dy3+ and Cr3+ emissions, ii) using the double excitation approach, and iii) using Cr3+ emission only, with relative sensitivities of 0.64 %K−1 at 175 K, 0.96 %K−1 at 200 K and 2.2 %K−1 at 200 K, respectively.
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•Multiparametric luminescence thermometry with Dy3+, Cr3+ double activated YAG.•PL consists of blue and yellow Dy3+ emissions and the broad, deep red Cr3+ emission.•Efficient energy transfer (~90%) from Dy3+ to Cr3+ in theYAG host.•LIR using: i) Dy3+ and Cr3+ emissions, ii) double excitation, and iii) Cr3+ emission.•Sr of i) 0.64 %K−1 at 175 K, ii) 0.96 %K−1 at 200 K and iii) 2.2 %K−1 at 200 K.
Colloidal stabilization of magnetic nanoparticles is one of the most important steps in the preparation of magnetic nanoparticles for potential biomedical applications. A special kind of magnetic ...nanoparticle are barium hexaferrite nanoplatelets (BSHF NPLs) with a hexagonal shape and a permanent magnetic moment. One strategy for the stabilization of BHF in aqueous media is to use coatings. In our research, we used an eco-friendly tannic acid, as a coating on BSHF NPLs. As-prepared BSHF NPLs coated with tannic acid were examined with transmission electron microscopy, infrared and UV-Vis spectroscopy, electro-kinetic measurements, and their room-temperature magnetic properties were measured. Stable colloids were tested in two biological complex media and antimicrobial properties of the material were examined. To enhance the antimicrobial properties of our material, we used tannic acid as a platform for the in-situ production of silver on BSHF NPLs. New hybrid material with silver also possesses magnetic properties and excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus.
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•Hard magnetic barium-hexaferrite nanoplatelets (NPLs) are coated with tannic acid.•Coating enhanced colloidal stability of NPLs in water and complex biological media.•Tannic acid was a platform for the in-situ production of silver onto NPLs.•The new hybrid is magnetic and has excellent antimicrobial activity.
This paper presents four new temperature readout approaches to luminescence nanothermometry in spectral regions of biological transparency demonstrated on Yb3+/Er3+-doped yttrium aluminum garnet ...nanoparticles. Under the 10 638 cm−1 excitation, down-shifting near infrared emissions (>10 000 cm−1) are identified as those originating from Yb3+ ions' 2F5/2 → 2F7/2 (∼9709 cm−1) and Er3+ ions' 4I13/2 → 4I15/2 (∼6494 cm−1) electronic transitions and used for 4 conceptually different luminescence thermometry approaches. Observed variations in luminescence parameters with temperature offered an exceptional base for studying multiparametric temperature readouts. These include the temperature-dependence of: (i) intensity ratio between emissions from Stark components of Er3+ 4I13/2 level; (ii) intensity ratio between emissions of Yb3+ (2F5/2 → 2F7/2 transition) and Er3+ (4I13/2 → 4I15/2 transition); (iii) band shift and bandwidth and (iv) lifetime of the Yb3+ emission (2F5/2 → 2F7/2 transition) with maximal sensitivities of 1% K−1, 0.8% K−1, 0.09 cm−1 K−1, 0.46% K−1 and 0.86% K−1, respectively. The multimodal temperature readout provided by this material enables its application in different luminescence thermometry setups as well as improved the reliability of the temperature sensing by the cross-validation between measurements.
The luminescence thermometry based on the intensity ratio of Cr3+ and host emissions in the Cr3+ activated MgTiO3 phosphor powder is demonstrated over the 100–350 K temperature range. Phosphor was ...prepared by a two-step procedure based on the sol-gel and molten salt methods. Rhombohedral crystal structure of the material is confirmed by X-ray diffraction analysis, and the mean crystallite size of the powder was calculated to be ~ 32 nm. Morphology was investigated using scanning electron microscopy showing ellipsoidal, densely packed grains with 100 nm–150 nm average size. Photoluminescence emission spectra recorded under 385 nm excitation showed the broad host emission centered at ~ 485 nm and the Cr3+ emission around ~ 700 nm. The temperature-dependent emission spectra showed that host-emission intensity is almost temperature invariant, while the intensity of the Cr3+ emission rapidly decreases from 200 K to 350 K. Such behavior theoretically modelled and further applied for the ratiometric luminescence temperature sensing showed the maximal relative sensitivity of ~ 2.6% K-1, temperature resolution of 0.3 K, and excellent repeatability.
The emission of Er3+ provides three combinations of emission bands suitable for ratiometric luminescence thermometry. Two combinations utilize ratios of visible emissions (2H11/2→4I15/2 at 523 nm/ ...4S3/2→4I15/2 at 542 nm and 4F7/2→4I15/2 at 485 nm/ 4S3/2→4I15/2 at 545 nm), while emissions from the third combination are located in near-infrared, e.g., in the first biological window (2H11/2→4I13/2 at 793 nm/ 4S3/2→4I13/2 at 840 nm). Herein, we aimed to compare thermometric performances of these three different ratiometric readouts on account of their relative sensitivities, resolutions, and repeatability of measurements. For this aim, we prepared Yb3+,Er3+:YF3 nanopowders by oxide fluorination. The structure of the materials was confirmed by X-ray diffraction analysis and particle morphology was evaluated from FE-SEM measurements. Upconversion emission spectra were measured over the 293–473 K range upon excitation by 980 nm radiation. The obtained relative sensitivities on temperature for 523/542, 485/542, and 793/840 emission intensity ratios were 1.06 ± 0.02, 2.03 ± 0.23, and 0.98 ± 0.10%K−1 with temperature resolutions of 0.3, 0.7, and 1.8 K, respectively. The study showed that the higher relative temperature sensitivity does not necessarily lead to the more precise temperature measurement and better resolution, since it may be compromised by a larger uncertainty in measurement of low-intensity emission bands.
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