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[en] 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. © 2019 Elsevier B.V.
[en] Fluorapatite doped with rare-earth elements has a wide-range of biomedical applications. Here, a new type of fluorapatite nanocrystals doped with praseodymium (FAP-Pr) with excitation-emission profiles in visible part of the spectrum is fabricated. Energy levels of Pr3+ activator ion contain metastable multiplet states that offer the possibility of efficient multicolor emission lines in FAP nanocrystals. Three types of FAP-Pr nanocrystals with 0.1%, 0.5% and 1% atomic percent of Pr3+ (along with the undoped FAP control sample) are studied. Their novel chemical production method is described, the FAP-Pr nanocrystals structure, biocompatibility and the suitability for cell imaging are analyzed. Physicochemical characterization confirms crystals down to nanometer size. In addition, quantum-chemical calculation predicts that Pr3+ ions are incorporated into the FAP crystal lattice at Ca2 (6 h) sites. In vitro viability results shows that FAP-Pr nanocrystals are nontoxic to live cells. Additionally, the cell uptake of the FAP-Pr nanocrystals is studied using fluorescence-based widefield and confocal microscopy. The nanocrystals show characteristic green emission at 545 nm (3P0→3H5 transition of Pr3+ ion) and orange emission at 600 nm (1D2→3H4), which we use to discriminate from cell autofluorescence background. Orthogonal projections across 3D confocal stacks show that the nanocrystals are able to enter the cells positioning themselves within the cytoplasm. Overall, the new FAP-Pr nanocrystals are biocompatible and of the tested types, the 0.5% Pr3+ doped nanocrystals show the highest promise as a tracking nanoparticle probe for bioimaging applications. © 2019
[en] A theoretical model for approximate evaluation of CIE chromaticity coordinates from the Judd-Ofelt intensity parameters has been presented. By reviewing the photoluminescence properties of all the lanthanides, the model's applicability was restricted to Nd3+, Sm3+, Eu3+, Tb3+ and Dy3+. Explicit equations for calculation of CIE coordinates for each of the allowed lanthanides were tested on Y2O3:Eu3+, P2O5·ZnO·Al2O3·BaO·PbO:Tb3+, LiNbO3:Dy3+, LaF3:Sm3+, LaF3:Eu3+, Ca3Sc2Si3O12:Eu3+, and TeO2·TiO2·Nb2O5:Nd3+ by comparing the CIE coordinates of the actual spectra to the coordinates obtained from the Judd-Ofelt parameters, with overall adequate matching. © 2019 Elsevier B.V.
[en] In this paper we will be presenting JOES (Judd-Ofelt from Emission Spectra), an application software for calculation of the Judd-Ofelt intensity parameters and derived quantities from the emission spectra of Eu3+ doped materials. The program is written to be user friendly and it requires no previous experience in the field of study. This Free and Open-Source program written in JAVA, works on Windows, Linux and MAC OS operating systems. Program has been tested on three europium doped oxides with good luminescent properties: TiO2:Eu3+, ZrO2:Eu3+ and Nb2O5:Eu3+. We wish to give to the researchers this theoretical tool which can make the calculations easier, faster and more reliable. © 2018 Elsevier B.V.
[en] By time-resolved spectrsscopy the intrinsic emission spectrum of UO2MoO4 at 4.2 K is obtained. The main progressions in the vibronic structure are identified as couplings with the Asub(g) correlation field components of the symmetric and asymmetric UO2 stretching modes. The intrinsic zero-phonon line in the emission and excitation spectrum is shown to be split both by the crystal field and correlation field. The steady-state emission spectrum at 4.2 K ist dominated at emission from traps. The vibronic structure of the trap emission reveals that all traps are distorted uranyl groups. (orig.)
[en] The effect of 1 MeV electron irradiation and a 100sup(o)C annealing stage on the intensity of the U2 line at 1.1182eV is presented. Evidence is provided from intensity vs. excitation power measurements tha the U2 radiative recombination involves only a single exciton. Eight models are discussed, with a complex isoelectronic center being favored. (orig.)
[en] Ca(Tb)3Ga2Ge3O12 and Sr3[Y(Tb)]2Ge3O12 garnets provide a cubic lattice with trivalent terbium, a luminescent rare earth, in dodecahedral (8 oxygen neighbors) and in octahedral (6 oxygen neighbors) sites, respectively. In the materials examined, Tb3+ in octahedral sites has a narrower fluorescence emission spectrum, higher luminescence efficiency and a longer lifetime than in dodecahedral sites. The luminescence properties and the unit cell size of the Ca3Y2Ge3O12 garnet, where Tb3+ is expected to be located on octahedral sites, are between those of the CaGa and SrY garnets. All these garnets are phosphorescent. On the basis of the variation with temperature of the phosphorecence decay law, it is proposed that the radiative electron-hole recombination process proceeds via a tunneling mechanism at temperatures below the thermal glow peaks, and via a free carrier diffusion mechanism at temperatures above the thermal glow peaks. All three Tb3+-doped germanate garnets have sufficiently high efficiency and persistence under electron beam excitation to be suitable for practical phosphor applications. The strontium yttrium germanate-Tb material has a cathodoluminescence decay time nearly three times that of the commercial P53 garnet phosphor. (orig.)
[en] An excitation band at 300 nm corresponding to Ce3+ absorption is observed in pentaphosphate crystals containing Ce3+ and Nd3+ when the Nd3+ luminescence is monitored. The decay of excitation of Ce3+n crystals of pure cerium pentaphosphate, CeP5O14, follows single exponential kinetics with 22 +- 2 nsec lifetime. In Ce0sub(.)5Nd0sub(.)5P5O14 crystals, the Ce3+ lifetime is shortened to 3.8 +- 0.4 nsec as a result of efficient nonradiative energy transfer to the Nd3+ ions. (orig.)
[en] Photoluminescence spectra in heat-treated CdTe:P and undoped CdTe were studied at emperatures of 4.2-77K in the edge emission and the exciton emission region. Temperature dependences and excitation intensity dependences were measured, and the recombination mechanism of each emission line was identified. A change in recombination center with psub(C)sub(d) was studied. In a heavily doped crystal an acceptor A2 (66 meV) was dominant at low psub(C)sub(d) and the phosphorus acceptor (78 meV) at high psub(C)sub(d). A rather deep donor (about 35 meV) was also observed. In a lightly doped crystal the spectra were intermediate between those of the undoped and the heavily doped crystals, and the emission line due to the phosphorus acceptor was not observed. In an undoped crystal an acceptor A1 (52 meV) was dominant at low psub(C)sub(d) and the A2 acceptor at medium and high psub(C)sub(d). (orig.)
[en] The cathodoluminescence (2-6 keV incident electrons) observed from thorium (111) and (533) crystal faces was recorded and analyzed for surfaces produced under various conditions. The blue luminescence observed in the presence of a partial oxygen pressure approx. equal to 133 μPa (approx. equal to 10-6 Torr) was found to consist of a broad asymmetric major band that peaked around 468 nm on which weak bands or lines were superimposed at approximately 433, 489, 502, and 534 nm. The emission was almost totally extinguished in the presence of a partial CO pressure approx. equal to 133 μPa (approx. equal to 10-6 Torr). The thorium-oxygen cathodoluminescence (CL) is interpreted as arising from the formation of ThO2 and the excitation of luminescence centers by the incident electron beam and their subsequent decay. The major luminescence at 468 nm arises from F centers in ThO2. The weak bands at 433 and 534 nm may arise from surface F+ and F centers designated as Fsub(s)+ and Fsub(s). The former may also be due to an OH luminescence center. The two longer wavelength lines (489, 502 nm) superimposed on the broad major band at approximately 468 nm are interpreted as arising from Pr-3 impurities in the thorium lattice that gave rise to fluorescence of ThO. The cathodoluminescence spectra observed in the presence of CO, and (CO+O2) and (CO+H2) gas mixtures were consistent with an interpretation that O2 in the gas phase was required in order to obtain ThO2 on and below the surface to produce significant luminescence. Auger spectroscopy showed that exposure to CO left approximately as much oxygen on the surface as in the case of O2 but did not produce appreciable cathodoluminescence. (orig.)