•15 µm Ti-Sapphire photoluminescent coatings created by PEO for 20 min.•2Eg level Jahn-Teller splitting is 2195 cm−1, 10 Dq = 19300 cm−1.•Highest PL intensity at 720 nm obtained with 0.32 at% Ti ...concentration.•1180 cm−1 activation energy for temperature quenching; 594 K Debye temperature.•3.2 cm−1 K−1 bandshift sensitivity, and 0.19 K resolution for luminescence thermometry.
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15 µm thick Ti-Sapphire coatings were synthesised at room temperature by the plasma electrolytic oxidation (PEO) method for 20 min from the pure aluminium substrate and with the addition of the TiO2 particles in various concentrations in the supporting electrolyte. The coatings are featured by microscopic pores typical for PEO surfaces. The dominant is the alpha phase of alumina with the small presence of the gamma phase. The estimated average crystalline size is 41 nm. Ti is uniformly distributed in these polycrystalline ceramic coatings and does not affect morphology or phase content. Photoluminescence of PEO-created coatings shows typical absorption, excitation, and emission features of Ti-Sapphire with two broad-overlapping excitation bands in the green and blue spectral region due to the Jahn-Teller splitting of the 2Eg level and the Stokes shifted emission centred at 720 nm. 2Eg energy state splitting is equal to 2195 cm−1 and 10 Dq ≈ 19,300 cm−1. The highest emission intensity was observed in the coating prepared with the 0.1 g/L TiO2 powder concentration, i.e. 0.32 at% of incorporated Ti3+. Emission spectra recorded at temperatures ranging from 100 K to 300 K revealed the Mott-Seitz temperature dependence of emission intensity with the 1180 cm−1 activation energy. The fit to the McCumber-Sturge relation gave, for the first time, the value of Debye temperature of 594 K of Al2O3:Ti. Non-contact, luminescence temperature sensing from the temperature-induced changes in the emission bandwidth gave a high sensitivity of 3.2 cm−1 K−1 and 0.19 K temperature resolution. The PEO created Ti-sapphire coatings are a promising multifunctional barrier level – optical temperature sensor material for applications in harsh environments or on large aluminium surfaces. It shows potential to be used as a planar waveguide Ti-Sapphire laser active medium.
Abstract The excellent photoluminescent properties of graphene quantum dots (GQD) makes them suitable candidates for biomedical applications, but their cytotoxicity has not been extensively studied. ...Here we show that electrochemically produced GQD irradiated with blue light (470 nm, 1 W) generate reactive oxygen species, including singlet oxygen, and kill U251 human glioma cells by causing oxidative stress. The cell death induced by photoexcited GQD displayed morphological and/or biochemical characteristics of both apoptosis (phosphatidylserine externalization, caspase activation, DNA fragmentation) and autophagy (formation of autophagic vesicles, LC3-I/LC3-II conversion, degradation of autophagic target p62). Moreover, a genetic inactivation of autophagy-essential LC3B protein partly abrogated the photodynamic cytotoxicity of GQD. These data indicate potential usefulness of GQD in photodynamic therapy, but also raise concerns about their possible toxicity.
Herein, we investigate the performance of single- and multiparametric luminescence thermometry founded on the temperature-dependent spectral features of Ca6BaP4O17:Mn5+ near-infrared emission. The ...material was prepared by a conventional steady-state synthesis, and its photoluminescence emission was measured from 7500 to 10,000 cm−1 over the 293–373 K temperature range in 5 K increments. The spectra are composed of the emissions from 1E → 3A2 and 3T2 → 3A2 electronic transitions and Stokes and anti-Stokes vibronic sidebands at 320 cm−1 and 800 cm−1 from the maximum of 1E → 3A2 emission. Upon temperature increase, the 3T2 and Stokes bands gained in intensity while the maximum of 1E emission band is redshifted. We introduced the procedure for the linearization and feature scaling of input variables for linear multiparametric regression. Then, we experimentally determined accuracies and precisions of the luminescence thermometry based on luminescence intensity ratios between emissions from the 1E and 3T2 states, between Stokes and anti-Stokes emission sidebands, and at the 1E energy maximum. The multiparametric luminescence thermometry involving the same spectral features showed similar performance, comparable to the best single-parameter thermometry.
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.
In order to compare spectroscopic properties between nanosized and that in single crystal form of YPO4:Pr3+, temperature-dependence of the red emission from 3P0 → 3H4 and 1D2 → 3H4 transitions of ...YPO4:0.1 at. % Pr3+ nanopowders has been investigated in details. The emission spectra of the sample in size of 20 nm, under selective excitation at 3P2, measured at different temperatures, T = 10, 100, 200 and 300 K have been recorded. The variation of emission intensity of each 3P0 → 3H4 and 1D2 → 3H4 against temperature has been investigated. Several spectral lines constitute 1D2 → 3H4 emission, assigned to transitions between 1D2 and 3H4 Stark levels are observed with no noticeable shifts between them and those observed at the single crystal. It is found that 1D2 → 3H4 emission intensity dominates that of 3P0 → 3H4 transition, pointing out the high efficiency of the multiphonon relaxation (MPR) process from 3P0 to 1D2. Fitting the temperature dependence of 3P0 → 3H4 emission intensity permits to estimate the phonons and their energies involved in non-radiatively transition between 3P0 and 1D2 levels, which are found different from single crystal. Also, fitting the multiphonon relaxation (MPR) rates against temperature, extracted from the measured 1D2 lifetime gives information that seven phonons can be involved to bridge the gap between 1D2 and 1G4. Furthermore, the possibility to use the YPO4: 0.1 at. % Pr3+ in the nano-thermometry application in temperature range T = 10–300 K was investigated.
•Temperature-dependence of the red emission YPO4:Pr3+ nanophosphor has been studied.•The phonons and their energies involved between 3P0 and 1D2 are different from single crystal.•Seven high energy phonons are involved to can bridge the gap between 1D2 and 1G4 by MPR process.•The possibility to use the YPO4: Pr3+ in the nano-thermometry application was investigated.
Luminescence thermometry on europium doped TiO2 films, prepared by the plasma electrolytic oxidation, was investigated by the Luminescence Intensity Ratio method. The performance of the material for ...temperature sensing was tested from room temperature to 260 °C. The theoretical fit of the emission intensity ratio of Eu3+5D1→7F1 and 5D0→7F2 transitions revealed the energy difference between 5D1 and 5D0 levels of 1777 cm−1. Temperature sensitivity was calculated on the entire temperature range, with maximum value of 3.43 %K−1 at 293 K. The relationship between Judd-Ofelt and thermometric parameters was demonstrated, and further utilized for the calculation of the radiative transition probability, dipole strength and radiative lifetime of the 5D1→7F1 transition.
•The performance of the TiO2:Eu3+ for temperature sensing has been investigated.•TiO2:Eu3+ was prepared by the plasma electrolytic oxidation method.•High sensitivity was obtained by the Luminescence Intensity Ratio method.•The complete Judd-Ofelt analysis has been carried out.•Judd-Ofelt and thermometry together yield a new calculation method.
Herein, the ability of gamma irradiation to enhance the photoluminescence properties of graphene quantum dots (GQDs) was investigated. Different doses of γ-irradiation were used on GQDs to examine ...the way in which their structure and optical properties can be affected. The photoluminescence quantum yield was increased six times for the GQDs irradiated with high doses compared to the nonirradiated material. Both photoluminescence lifetime and values of optical band gap were increased with the dose of applied gamma irradiation. In addition, the exploitation of the gamma-irradiated GQDs as photosensitizers was examined by monitoring the production of singlet oxygen under UV illumination. The main outcome was that the GQDs irradiated at lower doses act as better photoproducers than the ones irradiated at higher doses. These results corroborate that the structural changes caused by gamma irradiation have a direct impact on GQD ability to produce singlet oxygen and their photostability under prolonged UV illumination. This makes low-dose irradiated GQDs promising candidates for photodynamic therapy.
Fluorescence excitation-emission matrices were measured for 111 samples of different types of beer and studied by the parallel factor analysis (PARAFAC). The 5-component PARAFAC model was found to ...suitably describes the beer fluorescence, accounting for 99.4% of the fluorescence variance in the measured set of samples, and providing the completely resolved excitation and emission spectra of each component. The model was chosen based on a model’s core consistency and split-half analysis. It is shown that beer fluorescence is the sum of fluorescence of aromatic amino acids (tryptophan, tyrosine, and phenylalanine), different forms of vitamin B, and phenolic compounds. Obtained PARAFAC model of beer fluorescence demonstrated the potential for the quantification and quality analysis of beer fluorophores and classification of different beer types.
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•Ruby multifunctional coatings were created by plasma electrolytic oxidation method.•Thermometry was investigated by LIR, lifetime and bandshift methods.•LIR gave ca. 5 %K−1 ...sensitivity and 0.06 K resolution. Lifetime gave 0.08 K resolution.•Ruby coatings have the highest perspective for temperature sensing in high iodizing environments.
Thermographic properties of Cr3+-doped Al2O3 coatings created by plasma electrolytic oxidation (PEO) are investigated. Scanning electron microscopy revealed dense coatings uniformly distributed over the aluminum surface with uniform elemental maps, confirming homogeneous distribution of chromium ions. X-ray diffraction analysis shows that created coatings consist of a mixture of alpha and gamma phase of alumina and that alpha-to-gamma phase ratio increases with PEO processing time. Room-temperature photoluminescent measurements revealed two deep-red, sharp emissions placed at 694 nm (R1 line) and 693 nm (R2 line) typical for Cr3+ in Al2O3 octahedral configuration. No evidence of broad 680−800 nm emission typical for alumina gamma phase is observed and emissions were predominantly attributed to the ruby α-Al2O3:Cr3+. The temperature is obtained from the coating’s emission using temperature-induced changes in: i) band shift of the R1 line, (ii) luminescence intensity ratio (LIR) between two Cr3+ R1,2 lines, and (iii) lifetime of the Cr3+ red emission with maximal sensitivities of 0.2 cm−1 K−1 @ 550 K, 4.8 % K−1 @ 20 K and 0.9 % K−1 @ 450 K, respectively.
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