Abstract Synthesis of new antibacterial agents is becoming increasingly important in light of the emerging antibiotic resistance. In the present study we report that electrochemically produced ...graphene quantum dots (GQD), a new class of carbon nanoparticles, generate reactive oxygen species when photoexcited (470 nm, 1 W), and kill two strains of pathogenic bacteria, methicillin-resistant Staphylococcus aureus and Escherichia coli . Bacterial killing was demonstrated by the reduction in number of bacterial colonies in a standard plate count method, the increase in propidium iodide uptake confirming the cell membrane damage, as well as by morphological defects visualized by atomic force microscopy. The induction of oxidative stress in bacteria exposed to photoexcited GQD was confirmed by staining with a redox-sensitive fluorochrome dihydrorhodamine 123. Neither GQD nor light exposure alone were able to cause oxidative stress and reduce the viability of bacteria. Importantly, mouse spleen cells were markedly less sensitive in the same experimental conditions, thus indicating a fairly selective antibacterial photodynamic action of GQD.
Highlights • Color and translucency of model composites were affected primarily by the type of monomer. • Color stability was greatly affected by monomer and to a lesser extent by photoinitiator. • ...TPO-containing composites showed greater color stability than CQ-containing composites. • Milk added to black tea reduced the staining potential of tea.
Eu(III)-doped GdVO4 nanocrystals were prepared by precipitation of the Gd(III) and (Eu(III) citrate complexes, with fractions of Eu(III) ranging from 5 to 100mol%. Their red fluorescence is strongly ...quenched by H2O2, and this finding forms the basis for a fluorometric assay for H2O2 with a limit of detection as low as 1.6μM. The probe was further employed to design a highly sensitive enzymatic assay for glucose.
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•Synthesis of fluorescent nanocrystals (NCs) of type GdVO4 and doped with varying fractions of Eu(III) ions.•The NCs are shown to be viable fluorescent probes for hydrogen peroxide.•The NCs can be used as probes for sensing glucose via the hydrogen peroxide produced by enzymatic action of glucose oxidase.•Detection limits are as low as 1.6μM for H2O2 and 2.1μM for glucose.
The authors describe the preparation of Eu3+-doped GdVO4 nanocrystals (NCs) by precipitation of the Gd3+(Eu3+)-citrate complex which was then converted to the respective vanadate by dialysis. The fractions of Eu3+ ranged from 5 to 100mol%. The NCs were characterized by XRD, TEM, ICP-OES and dynamic light scattering which revealed that they possess superior colloidal stability in aqueous solutions in that no precipitation can be observed even after several months. The NCs display red and largely red-shifted fluorescence (peaking at 618nm) on photoexcitation at around 300nm. Fluorescence is strongly quenched by hydrogen peroxide. It is also shown that the fraction of doping with Eu3+ strongly affects quenchability. Most efficient quenching by H2O2 is observed if the NCs are doped with 50% of Eu3+. The findings were exploited to develop a fluorometric assay for H2O2 that works in the 5 to 250μM concentration range, with a limit of detection as low as 1.6μM (at a signal-to-noise ratio of 3). The probe was further employed to design a highly sensitive enzymatic assay for glucose via measurement of the quantity of H2O2 formed as a result of the catalytic action of glucose oxidase.
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•Photoluminescence of YVO4 doped with 1% Eu3+ and Dy3+ were recorded up to 733 K.•Thermometry by luminescence intensity ratio, line-shift and line broadening methods.•Experimental ...data of all three methods is fitted with excellent agreement with theory•Sensitivities were estimated for all three methods.•YVO4:Eu3+ and YVO4:Dy3+ are excellent thermographic phosphors.
Photoluminescence spectra of bulk YVO4 doped with 1 mol% of Eu3+ and Dy3+ were recorded on the range from room temperature to 733 K, in 20 K steps. The temperature sensing performances were estimated by the luminescence intensity ratio, line-broadening and line-shift methods. The luminescence intensity ratio was tested by the ratio of intensities of 5D1→7F1 and 5D0→7F2,4 transitions of Eu3+, and 4I15/2→6H15/2 and 4F9/2→6H15/2 transitions of Dy3+. The temperature dependent line-broadenings were measured on 5D0→7F2 and 4F9/2→6H13/2 of Eu3+ and Dy3+, respectively. The line-shifts were investigated on 5D0→7F1 and 4F9/2→6H15/2 of Eu3+ and Dy3+, respectively. The experimental data of all three methods is fitted and is in excellent agreement with the theory. The calculated thermometric figures of merit, absolute and relative sensitivities, show the sensor performances at the given temperature, and allow the selection of the best sensor material or transition to be chosen for the desired temperature range.
An extension of the Judd-Ofelt theory, a theoretical model to the field of Luminescence intensity ratio method in phosphor thermometry has been presented, that enables a calculation of thermometric ...figures of merit: sensitivity, maximum sensitivity and temperature resolution, by the Judd-Ofelt intensity parameters. The model is applicable for 7 out of 14 lanthanides, and as a testing ground for the model's adequacy, Y2O3 doped with three different Eu3+ concentrations had been chosen. PL spectra were recorded up to 480 °C and photoluminescence and thermometric properties have been obtained. Conventionally estimated thermometric figures of merit have been compared to those obtained by a Judd-Ofelt thermometric model, with a good matching. Consequently, a novel method for calculation of magnetic dipole strength of the mixed induced electric dipole and magnetic dipole transition has been developed. Additionally, an interactive application software has been developed for the quick evaluation of the sensitivity and temperature resolution from Judd-Ofelt intensity parameters.
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•Judd-Ofelt model for predicting thermometric sensor properties is presented.•Sensitivities and temperature resolutions can be estimated from Judd-Ofelt parameters.•Model is tested on Y2O3:Eu3+ up to 480 °C with good matching to experiment.•Explicit model equations for 7 lanthanides are presented.•Software for predicting sensor properties is created for fast calculation.
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•A new approximation to McCumber-Sturge relation has been introduced.•Bandshift of luminescence peaks is modelled without polylogarithmic functions.•Approximation allows for the ...extraction of the Debye temperature and coupling parameter.•The approximation works better at lower temperatures than Walsh and Di Bartolo approximation.
Temperature-induced bandshift of luminescence peaks is frequently described with McCumber-Sturge relation which is difficult for fitting or practical applications due to its mathematical complexity. Here for the first time, we give its exact solution in terms of polylogarithms, and an excellent approximation that is better at lower temperatures than the approximation by Walsh and Di Bartolo (WB). The novel approximation is analytically compared with that of WB, clearly giving the preferred temperature and Debye temperature ranges for each approximation. Three additional approximations are given, each with lowered complexity, until the equivalent quadratic form of Magomedov’s approximation is reached. All approximations are compared for their complexity vs applicable temperature range.
The binary luminescence thermometry probe is prepared from Y2O3:Ho3+ and Mg2TiO4:Mn4+ powders. This probe facilitates self‐referencing temperature readouts with excellent repeatability from both ...emission intensity ratio and excited state lifetimes. The ratio of intensities of Mn4+ deep red emission from 2E, 4T2→4A2 electronic transitions, and Ho3+ green emission from 5F4,5S2 →5I8 electronic transitions provides temperature measurements over the room temperature to 100 °C temperature range with a superior relative sensitivity of 4.6% °C−1 and temperature resolution of 0.1 °C. Over the same temperature range, the temperature readout from the Mn4+ emission lifetime offers measurements with relative sensitivity better than 0.5% °C−1 and better than 0.2 °C in resolution.
The combination of Mn4+ and Ho3+ emissions facilitates highly sensitive and repeatable luminescence thermometry. It shows a superior temperature resolution which can be realized using cheap blue LED sources and which covers the most relevant temperature range from room temperature to 100 °C.
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.
MgTiO3 nanoparticles doped with Mn4+, with homogeneous size ranging about 63.1 ± 9.8 nm, were synthesized by a molten salt assisted sol gel method. These nanoparticles have been investigated as ...optical thermal sensors. The luminescence of tetravalent manganese ion in octahedral environment within the perovskite host presents drastic variations with temperature. Three different thermometry approaches have been proposed and characterized. Two luminescence intensity ratios are studied. Firstly between the two R-lines of Mn4+ emission at low temperature (−250 °C and −90 °C) with a maximal sensitivity of 0.9% °C−1, but also secondly between 2E → 4A2 (R-line) and the 4T2 → 4A2 transitions. This allows studying the temperature variation within a larger temperature range (−200 °C to 50 °C) with a sensitivity between 0.6% °C−1 and 1.2% °C−1 over this range. The last proposed method is the study of the lifetime variation versus temperature. The effective lifetime value corresponds to a combination of transitions from two excited energy levels of the tetravalent manganese (2E and 4T2) in thermal equilibrium toward the fundamental 4A2 state. Since the more energetic transition (4T2 → 4A2) is spin-allowed, contrary to the 2E → 4A2 one, the lifetime drastically decreases with the increase in temperature leading to an impressive high sensitivity value of 4.1% °C−1 at 4 °C and an exceptional temperature resolution of 0.025 °C. According to their optical features, MgTiO3:Mn4+ nanoparticles are indeed suitable candidates for the luminescence temperature probes at the nanoscale over several temperature ranges.
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.
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