Ratiometric luminescence thermometry employing luminescence within the biological transparency windows provides high potential for biothermal imaging. Nd3+ is a promising candidate for that purpose ...due to its intense radiative transitions within biological windows (BWs) I and II and the simultaneous efficient excitability within BW I. This makes Nd3+ almost unique among all lanthanides. Typically, emission from the two 4F3/2 crystal field levels is used for thermometry but the small ~100 cm−1 energy separation limits the sensitivity. A higher sensitivity for physiological temperatures is possible using the luminescence intensity ratio (LIR) of the emissive transitions from the 4F5/2 and 4F3/2 excited spin-orbit levels. Herein, we demonstrate and discuss various pitfalls that can occur in Boltzmann thermometry if this particular LIR is used for physiological temperature sensing. Both microcrystalline, dilute (0.1%) Nd3+-doped LaPO4 and LaPO4: x% Nd3+ (x = 2, 5, 10, 25, 100) nanocrystals serve as an illustrative example. Besides structural and optical characterization of those luminescent thermometers, the impact and consequences of the Nd3+ concentration on their luminescence and performance as Boltzmann-based thermometers are analyzed. For low Nd3+ concentrations, Boltzmann equilibrium starts just around 300 K. At higher Nd3+ concentrations, cross-relaxation processes enhance the decay rates of the 4F3/2 and 4F5/2 levels making the decay faster than the equilibration rates between the levels. It is shown that the onset of the useful temperature sensing range shifts to higher temperatures, even above ~ 450 K for Nd concentrations over 5%. A microscopic explanation for pitfalls in Boltzmann thermometry with Nd3+ is finally given and guidelines for the usability of this lanthanide ion in the field of physiological temperature sensing are elaborated. Insight in competition between thermal coupling through non-radiative transitions and population decay through cross-relaxation of the 4F5/2 and 4F3/2 spin-orbit levels of Nd3+ makes it possible to tailor the thermometric performance of Nd3+ to enable physiological temperature sensing.
Due to their unique structural properties bacterial cellulose (BC) hydrogels find possible usage in many fields such as cosmetology, food industry, or medicine. In this study, photoactive BC ...hydrogels are investigated through modifications of their structural, mechanical, and pro‐oxidant properties resulting from graphene quantum dots (GQDs) encapsulation. Detailed structural analysis is conducted by atomic force microscopy, transmission electron microscopy and scanning electron microscopy, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction method. Dynamic mechanical analysis is performed to study the changes in storage modulus, loss modulus and tan δ. Pro‐oxidative properties of new designed composites are tested by electron paramagnetic resonance (EPR). Structural and mechanical analyses show successful encapsulation of GQDs into BC whereas EPR measurements indicate high potential of these composites for singlet oxygen production.
Photoactive GQDs‐BC composite hydrogels are produced by immersing BC in GQDs acetone solution. Detailed structural, chemical and mechanical analyses show that photoactive GQDs are encapsulated into BC polymer matrix. Porosity test shows significant pore enlargement of GQDs‐BC composite hydrogels. Composite hydrogels are highly potent oxygen radical generator and present advanced material for wound dressing application.
When activated by Dy
3+
, Na
0.25
K
0.25
Bi
0.50
TiO
3
(NKBT), piezoelectric powders show strong luminescence in the blue and yellow spectral range. Emissions of this material can be effectively ...utilized for both luminescence intensity ratio and lifetime-based readouts of temperature. Photoluminescence measurements over a temperature range of 293–483 K show that the luminescence intensity ratio temperature readout has maximal relative sensitivity of 1.93% K
−1
at 380 K, while the relative sensitivity of the lifetime temperature readout reaches 1.1% K
−1
at 480 K. For this study, materials were synthesized by a solid-state reaction using TiO
2
, Bi
2
O
3
, Na
2
CO
3
, K
2
CO
3
and Dy
2
O
3
as precursors. X-ray diffraction measurements showed that the NKBT sample crystallized in the A-site substituted distorted perovskite rhombohedral structure (
R
3
c
symmetry). The photoluminescence spectra showed characteristic emission bands of Dy
3+
ions centered at 457 nm (
4
I
15/2
→
6
H
15/2
), 478 nm (
4
F
9/2
→
6
H
15/2
), 574 nm (
4
F
9/2
→
6
H
13/2
) and 663 nm (
4
F
9/2
→
6
H
11/2
). The ratio of emissions from
4
F
9/2
and
4
I
15/2
excited states to the
6
H
15/2
ground state was used as a luminescence intensity ratio indicator of temperature, while the decay of emission from
4
F
9/2
→
6
H
13/2
transition was used as a lifetime indicator of temperature. CIE coordinates
x
= 0.326 and
y
= 0.361 calculated from room temperature emission spectra show the perspective of this material for use in white light emission devices.
Abstract
The near-infrared luminescence of Ca
6
Ba(PO
4
)
4
O:Mn
5+
is demonstrated and explained. When excited into the broad and strong absorption band that spans the 500–1000 nm spectral range, ...this phosphor provides an ultranarrow (FWHM = 5 nm) emission centered at 1140 nm that originates from a spin-forbidden
1
E →
3
A
2
transition with a 37.5% internal quantum efficiency and an excited-state lifetime of about 350 μs. We derived the crystal field and Racah parameters and calculated the appropriate Tanabe–Sugano diagram for this phosphor. We found that
1
E emission quenches due to the thermally-assisted cross-over with the
3
T
2
state and that the relatively high Debye temperature of 783 K of Ca
6
Ba(PO
4
)
4
O facilitates efficient emission. Since Ca
6
Ba(PO
4
)
4
O also provides efficient yellow emission of the Eu
2+
dopant, we calculated and explained its electronic band structure, the partial and total density of states, effective Mulliken charges of all ions, elastic constants, Debye temperature, and vibrational spectra. Finally, we demonstrated the application of phosphor in a luminescence intensity ratio thermometry and obtained a relative sensitivity of 1.92%K
−1
and a temperature resolution of 0.2 K in the range of physiological temperatures.
Therapy of bacterial urinary tract infections (UTIs) and catheter associated urinary tract infections (CAUTIs) is still a great challenge because of the resistance of bacteria to nowadays used ...antibiotics and encrustation of catheters. Bacterial cellulose (BC) as a biocompatible material with a high porosity allows incorporation of different materials in its three dimensional network structure. In this work a low molecular weight chitosan (Chi) polymer is incorporated in BC with different concentrations. Different characterization techniques are used to investigate structural and optical properties of these composites. Radical scavenging activity test shows moderate antioxidant activity of these biocompatible composites whereas
in vitro
release test shows that 13.3% of chitosan is released after 72 h. Antibacterial testing of BC-Chi composites conducted on Gram-positive and Gram-negative bacteria causing UTIs and CAUTIs (
Escherichia coli
,
Pseudomonas aeruginosa
,
Klebsiella pneumoniae
) and encrustation (
Proteus mirabilis
) show bactericidal effect. The morphology analysis of bacteria after the application of BC-Chi shows that they are flattened with a rough surface, with a tendency to agglomerate and with decreased length and width. All obtained results show that BC-Chi composites might be considered as potential biomedical agents in treatment of UTIs and CAUTIs and as a urinary catheter coating in encrustation prevention.
Bacterial cellulose-chitosan composite with antibacterial and moderate antioxidant activity for potential UTI/CAUTI treatment and catheter coating in encrustation prevention.
A promising way to improve the performance of luminescent materials is to combine them with noble metal nanoparticles. Herein, a set of silver/europium-doped lanthanum orthophosphate ...(Ag/La0.95Eu0.05PO4) nanostructures with different concentrations of silver nanoparticles were prepared and investigated. The presented overlap between the strongest europium (Eu3+) excitation line and the broad silver nanoparticle surface plasmon resonance makes the combination prospective for coupling. X-ray powder diffraction confirmed the monoclinic monazite structure. The transmission electron microscopy revealed particles with a rod-like shape and ~4 aspect ratio. Photoluminescence spectra show characteristic Eu3+ ion red emission. One of the requirements for an enhanced luminescence effect is the precise control of the distance between the noble metal nanoparticles and the emitter ion. The distance is indirectly varied throughout the change of Ag nanoparticle concentration in the La0.95Eu0.05PO4 host. The emission intensity increases with the increase in Ag nanoparticles up to 0.6 mol %, after which the luminescence decreases due to the nanoparticles’ close packing and aggregation leading to the displacement of La0.95Eu0.05PO4 from the vicinity of the metal particles and reabsorption of the emitted light. The emission intensity of La0.95Eu0.05PO4 increases more than three times when the Eu3+ excitation is supported by the localized surface plasmon resonance in the Ag/La0.95Eu0.05PO4 nanostructures.
Lanthanide‐doped vanadate thin films offer (i) a promising platform for luminescence‐based noncontact temperature sensing; (ii) ratiometric/self‐referencing absolute measurements; (iii) exceptional ...repeatability and reversibility for multirun uses and a long life cycle; (iv) 2% K−1 maximum temperature sensitivity (among the highest recorded for inorganic nanothermometers); (v) a temperature resolution greater than 0.5 K; and (vi) the potential for high‐resolution 2D temperature mapping.
Bacterial infection and their resistance to known antibiotics delays wound healing. In this study, nanochitosan dots (nChiD) produced by gamma irradiation have been encapsulated in bacterial ...cellulose (BC) polymer matrix to study the antibacterial potentials of these nanocomposites and their possible usage in wound healing treatment (scratch assay). Detailed analyses show that nChiDs have disc-like shape and average diameter in the range of 40 to 60 nm depending of the applied dose. All nChiDs as well as BC-nChiD nanocomposites emit green photoluminescence independently on the excitation wavelengths. The new designed nanocomposites do not have a cytotoxic effect; antioxidant analysis shows their moderate radical scavenging activity whereas antibacterial properties show significant growth inhibition of strains mostly found in difficult-to-heal wounds. The obtained results confirm that new designed BC-nChiD nanocomposites might be potential agent in wound healing treatment.
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•New innovative approach for wound healing treatment•Photoactive nanochitosan dots produced by gamma irradiation•Encapsulation of nanochitosan dots in bacterial cellulose•Nanochitosan dots/bacterial cellulose nanocomposite as moderate antioxidant agent•Nanochitosan dots/bacterial cellulose nanocomposite as strong bactericidal agent
La(PO3)3 activated with different concentrations of Pr3+ was synthesized by a solid-state process. The obtained powder was composed of chunks of several microns in size, typical for this type of ...synthesis. X-ray diffraction confirmed an orthorhombic crystal structure with the C2221 space group. The electronic band structures and density of states of La(PO3)3 and La(PO3)3:Pr3+ are calculated and presented. The visible and near-infrared emissions from Pr3+ Xe4f2→ Xe4f2 electronic transitions were detected under 442 nm excitation. The red emission from the 1D2 state dominates visible spectra while emissions from the 3P0,1,2 states have smaller intensities. The 1D2 emission centered around 1020 nm is detected in the near-infrared spectral range. Intensities of 3P0 emissions increased with an increase in Pr concentration, while 1D2 emissions decreased in intensity. We found that the main process responsible for the 1D2 state decay is the Pr(1D2) + Pr(3H4) → Pr(1G4) + Pr(3F3,4) cross-relaxation between two Pr ions of electric dipole-dipole character. This finding is supported by 1D2 emission decay measurements, which revealed a reduction of average decay constants from 242 μs for a 0.5 mol% doped sample to 11 μs for a 10 mol% doped sample and an increasingly stronger non-exponential behavior of emission decay patterns with an increase in Pr3+ concentration.
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•La(PO3)3:Pr3+ powders were synthesized by a solid-state process.•Visible and near-infrared emissions from Pr3+ were analyzed.•Electronic band structures and density of states of La(PO3)3:Pr3+ were calculated.•Pr3+ (1D2) + (3H4) → (1G4) + (3F3,4) cross-relaxation process was identified.
•Eu3+, Mn4+ co-doped YAG for dual-activated luminescence intensity ratio thermometry.•Modified pechini method for body-centered cubic structure with crystallite size ∼20 nm.•PL spectra with emissions ...in red spectral region from both Eu3+and Mn4+transitions.•Suppression of Eu3+ emission reveals efficient Eu3+ → Mn4+ energy transfer.•Eu3+ 5D0→7F1 / Mn4+ 2E→4A2 LIR for SAmax = 19.2mK−1 @351 K and SRmax = 5.06%K − 1 @321 K.
Potential of Eu3+, Mn4+ co-doped YAG for dual-activated luminescence intensity ratio thermometry is investigated. The samples were prepared by modified Pechini method and cubic structure confirmed by X-ray diffraction with average crystallite size of ∼ 20 nm. Scanning electron microscopy revealed different sized chunks composed of ellipsoidal-shaped particles bellow 50 nm. Temperature-dependent photoluminescent emission spectra (λex = 465 nm, 98–473 K temperature range) of co-doped samples consist of emission bands in the red spectral region originating from both Eu3+and Mn4+transitions. Concentration of Mn4+ and Eu3+ is optimized to be 0.5mol% and 3mol%. Observed suppression of Eu3+ emission indicate an efficient (∼97%) energy transfer from Eu3+ to Mn4+. Using luminescence intensity ratio as the ratio between the integrated intensities of the Eu3+ 5D0→7F1 transition and the Mn4+ 2E→4A2manyfold, maximal absolute and relative sensitivities of SAmax = 19.2mK−1 at 351 K and SRmax = 5.06%K − 1 at 321 K were calculated.
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