Phase transition, radio- and photoluminescence of K3Lu(PO4)2 doped with Pr3+ ions

Luminescent characteristics of K3Lu(PO4)2:Pr3+ (1 and 5 mol.%) microcrystalline powders, a promising optical material for scintillation applications, were investigated using various experimental techniques. The material shows emission features connected with both high intensity interconfigurational 4f15d→4f2 transitions (broad UV emission bands) and intraconfigurational 4f2→4f2 transitions (weak emission lines in the visible range). The output of X-ray excited 4f15d→4f2 emission of Pr3+ increases with a temperature rise from 90 K to room tem- perature and higher depending on the Pr3+ ions concentration. The high 5% concentration of Pr3+ ions is found to be favourable for the stabilization of a monoclinic phase (P21/m space group) over a trigonal one (P3 space group) while emission properties of the material reveal that a phase transition occurs at higher temperatures. Decay kinetics of Pr3+ 4f15d→4f2 emission are recorded upon excitation with high repetition rate X-ray syn- chrotron excitation and pulse cathode ray excitation. Issues related to a non-exponential decay of luminescence and presence of slow decay components are discussed in terms of energy transfer dynamics. The presence of defects was revealed with thermoluminescence measurements and these are suggested to be the mainly responsible for delayed recombination of charge carriers on the Pr3+ 4f15d states. Some peculiarities of host-to- impurity energy transfer are discusse

Action recognition using single-pixel time-of-flight detection

Action recognition is a challenging task that plays an important role in many robotic systems, which highly depend on visual input feeds. However, due to privacy concerns, it is important to find a method which can recognise actions without using visual feed. In this paper, we propose a concept for detecting actions while preserving the test subject's privacy. Our proposed method relies only on recording the temporal evolution of light pulses scattered back from the scene. Such data trace to record one action contains a sequence of one-dimensional arrays of voltage values acquired by a single-pixel detector at 1 GHz repetition rate. Information about both the distance to the object and its shape are embedded in the traces. We apply machine learning in the form of recurrent neural networks for data analysis and demonstrate successful action recognition. The experimental results show that our proposed method could achieve on average 96.47 % accuracy on the actions walking forward, walking backwards, sitting down, standing up and waving hand, using recurrent neural network

Optical and luminescence characterization of LiBaAlF6 single crystals

Far ultraviolet optical, luminescence excitation and pulse cathodoluminescence spectroscopy methods were used to determine the electronic structure properties of undoped single crystals of LiBaAlF6 (LBAF). The spectrum of the refraction index in the ultraviolet–visible range was recorded. The photoluminescence excitation spectroscopy was carried out for both the excitonic (4.3 eV) and fast vacuum ultraviolet (6.6 eV) emission bands of LBAF single crystals at 10 K. Modeling of the photoluminescence excitation spectra for excitonic emission was performed to characterize the low-energy tail of the host absorption of LBAF single crystals. The pulse cathodoluminescence spectroscopy method was used to characterize the fast vacuum ultraviolet (6.6 eV) emission band and proof its origination from the radiative core-valence transitions F− 2p →→ Ba2+ 5p

Electronic Properties of undoped LiBaAlF6LiBaAlF_6 Single Crystals: Far-Ultraviolet Optical, Luminescence, and X-Ray Photoelectron Spectroscopy Studies

The electronic structure properties of undoped single crystals of LiBaAlF6 (LBAF) were determined using low-temperature (T=10  K) time-resolved far-ultraviolet (3.7–40 eV) synchrotron radiation spectroscopy, calculations for the spectra of optical functions, and x-ray photoelectron spectroscopy. The bandgap of the investigated compound was found at Eg=12.3  eV, the energy threshold for creation of the unrelaxed excitons at En=1=11.6  eV, and the low-energy fundamental absorption edge at 11.0 eV. The subnanosecond photoluminescence emission band at 6.6 eV in LBAF single crystal is due to radiative valence-core transitions 2p F−→5p Ba2+

Luminescence properties and energy transfer processes in LiSrPO4 doped with Pr3+ and co-doped with Na+ and Mg2+

The paper studies the influence of co-doping with alkali metal ions (Na+, Mg2+) on fast interconfigurational 5d-4f luminescence in LiSrPO4 doped with Pr3+. Na+ and Mg2+ ions were introduced in order to provide charge compensation and modify the electronic configuration of the materials. Luminescent properties of the powder samples were investigated using time-resolved pulsed cathodoluminescence and luminescence spectroscopy in the UV-VUV spectral region. The obtained results were compared with those obtained earlier on LiSrPO4:Pr3+ without co-dopants. With introduction of the co-dopants, slight changes in relative luminescence intensity and decay time of Pr3+ ion 4f15d1-4f2 radiative transitions were found. The study revealed a complex interplay be- tween defects of crystalline structure and impurity ions leading to the peculiarities in energy relaxation pro- cesses. Energy transfer leading to the delayed recombination processes is responsible for significant afterglow in Pr3+4f15d1-4f2 emissio

Optical and luminescence spectroscopy studies of electronic structure of Li6GdB3O9Li_6GdB_3O_9 single crystals

This article presents the study of electronic structure of Li6GdB3O9 single crystals and radiative relaxation of electronic excitations in them. The investigation was performed by the means of low-temperature optical and luminescence far-ultraviolet spectroscopy upon excitation by synchrotron radiation. On the basis of the low-temperature (T = 10 and 30 K) spectra of the reflection, recorded in the present research and the dispersions of the complex optical functions of View the MathML sourceεˆ(E),nˆ(E) and μ(E)μ(E), calculated in the framework of the oscillator model, we have determined the parameters of the electronic structure of the Li6GdB3O9 crystals as follows. The value of the minimum energy for the interband transitions in the boron–oxygen framework is View the MathML sourceEg=9.42eV, the energy position of the first excitonic peak in the excitation spectra for anionic excitons is View the MathML sourceEn=1=7.46eV, the minimum threshold energy for excitation of excitons in linear chains of the Gd3+ cations is View the MathML sourceEc=6.80eV. The excitation spectra of an intrinsic luminescence of Li6GdB3O9 crystals, recorded at 10 K in the range of the optical charge-transfer transitions O–Gd have a band with the maximum at View the MathML sourceECT=6.57eV

Decay Kinetics of CeF3 under VUV and X-ray Synchrotron Radiation

Characteristic dimensions and evolution times of regions of secondary electronic excitations created by the interaction of ionizing radiation with matter cannot be measured directly. At the same time these are essential parameters both for engineering of nanostructured composite materials defining optimal layer thickness and nanoparticles radii and for the development of optimized scintillators. The paper demonstrates how such spatial and temporal data can be extracted from luminescence decay kinetics excited by vacuum ultraviolet (VUV) and X-ray photons at modern sources of synchrotron radiation MAX IV and PETRA III. Specific features of energy-band structure of self-activated crystal CeF 3 are discussed, and its potential for a super-fast detection of ionizing radiation evaluated. Diffusion-controlled dipole-dipole interaction of Frenkel excitons is demonstrated to account well for the luminescence non-exponential decay kinetics providing information on the scales of excited regions created by photons of different energy. For 20 eV photons the radius of excited regions is estimated to be 10 nm, and for 200 eV photons it increases to 18 nm. Effective radius of excited regions of complicated shape created by 19 keV is as large as 80 nm and the diffusion length of Frenkel excitons over radiative time is 14 nm

Luminescence properties of undoped LiBaAlF6\mathrm{LiBaAlF_{6}} single crystals

This paper presents the results of the study of electronic excitations in undoped LiBaAlF6 single crystals by means of luminescence spectroscopy and complimentary optical methods. The intrinsic emission at 4.2 eV due to self-trapped excitons was identified. The fast nanosecond defect-related luminescence was revealed at 3.0 eV. Both emissions degrade under electron beam irradiation, the most probable reason of which is defect creation introducing an additional non-radiative relaxation channel prohibiting energy transfer to luminescence centers. These defects can be recovered and luminescence intensity restored at higher temperatures (>200 K). The permanent damage by electron beam irradiation results only in overall growth of the absorption coefficient in the whole 1.5–6.5 eV spectral region studied. The analysis of thermally stimulated luminescence glow curves in the temperature range of 5–410 K revealed two shallow charge carrier traps with the activation energies of 0.22 and 0.33 eV, respectively. The luminescence of an impurity peaked at 2.5 eV was found and tentatively assigned to an oxygen-related emission center

Intraband luminescence excited in new ways: Low-power x-ray and electron beams

Hot intraband luminescence (IBL) was observed under excitation by high-power (120 keV, 10 A/cm2) pulsed electron beam, low-energy (10 keV) and low-current (2 μA) continuous electron beam as well as pulsed x-rays. Thus, the fundamental possibility of IBL excitation by x-rays was confirmed, and for most studied materials the absence of the dependence of IBL spectral shape on excitation energy was revealed. For the first time, the intraband luminescence was monitored under low-power excitation, which confirmed the absence of a power threshold of its mechanism and completely ruled out the role of excitation density effects in IBL formation. The data obtained allow the prediction that the IBL can be excited by single photons of 511-keV energy, which is required for enhancing scintillation time resolution in TOF-PET