Herein we report the study of the influence of synthesis conditions during the microwave-hydrothermal crystallization of freshly precipitated gels on the phase composition and morphology of the ...rare-earth doped yttrium orthophosphates nanoparticles. We characterize the nanoparticles of YPO sub(4) and YPO sub(4) times 0.8H sub(2)O using X-ray diffraction analysis, TEM, and FT-IR spectroscopy. Furthermore, we argue that for the given phase the degree of crystallinity and thus the sample morphology depend strongly on the synthesis conditions. We establish that the hexagonal hydrate phase can be obtained by means of microwave-hydrothermal method if one uses phosphate anion excess or adjusts pH of the reaction mixture. Also we show that the metastable hydrate phase is most likely stabilized by hydroxyl groups at elevated temperatures.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Possible Nd3+ positions in β-tricalcium phosphate were calculated by DFT methods.•Two types of charge compensation have been identified in Nd3+ doped β –TCP.•Low-temperature site-selective laser ...spectroscopy of Nd3+ doped β -TCP was done.•The position of eight Nd3+ optical centers (OCs) in β -TCP lattice was determined.•Two types of OCs, Nd-Nd pairs and Nd-OH were identified by energy transfer probe.
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We investigated the distribution of the Nd3+ impurity centers over five Ca2+ positions in the β-Ca3(PO4)2 lattice (space group R3c) using low-temperature site-selective laser spectroscopy and fluorescence kinetics measured by double spectral selection in combination with the results of periodic density functional theory (DFT) calculations. Site-selective fluorescence excitation spectra of the Nd3+ ion were measured by fine tuning the laser wavelength in the spectral band of the 4I9/2(1) → 4G5/2(1,2) transitions and by fluorescence detection in the spectral band of the 4F3/2(1) → 4I9/2(1,2) transitions. The kinetics of nonradiatiative energy transfer from the 4F3/2(1) crystal field (CF) level was used to probe the local structure of Nd3+ sites. Theoretical modelling of the replacement of Ca2+ ions by Nd3+ ions with different charge compensation schemes was carried out. In the context of heterovalent substitution, hydrothermal synthesis conditions, and charge-balance mechanisms, two structural models of substitution have been proposed and thoroughly studied: substitution by a single Nd3+ ion accompanied by a trapped hydroxyl group, and substitution with a pair of Nd3+ ions. Numerical modeling of possible substitution scenarios calculated for a large number of combinations of cation-exchange sites in the lattice was carried out. The results obtained were classified according to the parameters of the accommodation of impurities and the energies of defect formation. The most favorable configurations of the distribution of impurity Nd3+ cations in the β-Ca3(PO4)2 lattice were predicted. By combining the “energy transfer probe” analysis and the results of the structural modeling, a relationship was found between the local geometry and the spectral and kinetic properties of luminescence of the Nd3+ optical centers. This allowed us to accurately determine the local structural geometries of eight experimentally detected the Nd3+ optical centers among the various possibilities in the distribution of the dopant ions over five cationic positions in β-Ca3(PO4)2. Six optical centers represent different types of Nd3+ - Nd3+ pairs, the formation of which is energetically favorable for charge compensation according to the 3Ca2+ → 2Nd3+ + ⎕ scheme, when one calcium position remains vacant. Two optical centers are single centers of the Nd3+ ion in which the charge is compensated by negatively charged hydroxyl ions intercalated during hydrothermal synthesis according to the scheme Ca2+→ Nd3+ + OH−. It was assumed that these pairs are located in several structural cavities free of PO4 tetrahedra.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
We demonstrated the existence of entangled 4I9/2(1) x 4G5/2(1) quantum state in a pair of Nd3+ ions due to strong resonance quadrupole – quadrupole interaction between the ions. In doing so, we used ...narrow line (0.05 Å) tunable pulsed dye laser excitation of a 1% Nd3+: LaF3 crystal at liquid helium temperatures at the 4I9/2(1) → 4G5/2(1) transition and measured the site-selective near infrared (NIR) fluorescence spectra of different optical centers (OCs) at the 4F3/2(1) → 4I9/2(1) transition of Nd3+ with high spectral resolution (0.1 Å); the NIR fluorescence excitation spectra at the 4I9/2(1) → 4G5/2(1) transition (0.05 Å); and by varying the excitation and detection wavelengths we measured the IR fluorescence kinetics of the selected type of OCs. As a result, we observed inhomogeneous splitting within 30 cm−1 of wavenumbers for the fluorescence spectra at the 4F3/2(1) → 4I9/2(1) transition, manifested in the presence of numerous narrow inhomogeneously broadened spectral lines of different OCs. We have attributed each spectral line to a different single-site, pair, triple, or quad optical centers via analysis of the 4F3/2(1) metastable level fluorescence kinetics decay times. Each type of OCs demonstrates its own specific IR fluorescence excitation spectrum at the 4I9/2(1) → 4G5/2(1) transition detected in a 1%Nd3+: LaF3 crystal at 1.6 K. One of the spectral lines of the pair centers (with the frequency 17313.3 cm−1) exhibited the fine splitting with the value of 0.2 cm−1. The shape and the value of fine splitting are explained theoretically assuming that this line corresponds to the excitation of the entangled the 4I9/2(1) x 4G5/2(1) quantum state of the pair of Nd3+ ions located at short distance, R ~ 4.1 Å.
•We observed strong inhomogeneous splitting for the NIR fluorescence spectra of Nd3+ in 1 at.% Nd3+: LaF3 crystal at 1.6 K•We attributed each spectral line to a different single-site, pair, triple, or quad optical centers.•The spectral line of the pair center exhibited the fine splitting (0.2 cm−1).•The shape and the value of fine splitting are explained theoretically.•We confirmed the entangled 4I9/2(1) x 4G5/2(1) quantum state in a pair of Nd3+ ions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The paper deals with the development of methods for changing the surface properties of metals (copper, brass, aluminum-beryllium) under the action of an electron beam on the organic liquids in the ...near-surface metal layer. Metacrylic acid, tetraethoxysilane (TES), and hexamethyldisiloxane (HMDS) were used as metal surface modifiers. Parameters of pulsed high-current electron accelerator were as follows: kinetic electron energy 90 keV and beam current density 65 A/cm
2
. An analysis of the IR spectra showed that irradiation of the metal surfaces with an electron beam in the presence of methacrylic acid, TES, and HMDS leads to the fixation of organic compounds on these surfaces.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A comparative study of the sizes and spatial structure of single dielectric colloidal nanoparticles of lanthanum fluoride, doped with rare-earth neodymium ions (Nd
3+
:LaF
3
), and their ...conglomerates in an aqueous solution has been performed. Nanoparticles were synthesized by aqueous co-precipitation method with subsequent hydrothermal microwave (HTMW) treatment. Experiments were performed using three methods: transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and dynamic light scattering (DLS). An analysis of the results has shown that a stable colloidal solution of nanoparticles is formed during synthesis. The solution consists of single lanthanum fluoride nanoparticles, having a narrow (10–30 nm) size distribution, and nanoclusters formed on their basis. It is also shown that the spatial structure of nanoclusters cannot be described in terms of the fractal model, which is widely used to describe clusters formed in colloidal solutions of nanoparticles of various nature.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Pair centers of Nd3+ ions in the CdF2, CaF2, and SrF2 doped crystals at T=6.5K were studied under tunable narrow-linewidth laser excitation. It has been established that the exchange of electronic ...excitation leads to the splitting of the one-exciton cooperative 4G5/2(1) x 4I9/2(1) state by 2–3 cm−1 with a non-monotonic dependence on the distance between the ions in the pairs in these crystals. This dependence is explained by the competition of forced dipole-dipole and quadrupole-quadrupole interactions with spin flip. The high rate of such exchange mechanisms is due to strong spin–orbit interaction and small energy difference between the 4f levels of Nd3+ ions. It is shown that the pair centers in all one-exciton cooperative states, in contrast to the ground and two-exciton excited states, have nonzero static dipole moments. This makes it possible to use the latter states as ultrafast qubits, and one-exciton states as control qubit to implement a CNOT quantum gate.
•Nd3+ ion pairs in doped fluorite-type crystals are studied by narrow laser excitation.•Strong resonance exchange interaction splits the entangled 4G5/2(1) x 4I9/2(1) state.•Exchange transitions occur with spin-flip due to spin-orbit interaction.•No direct correlation between the splitting value and ion distance in pairs was found.•The splitting is due to quadrupole-quadrupole and forced dipole-dipole ion interaction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Using two-color excitation with narrow laser lines of 0.2 cm−1 and time-resolved site-selective fluorescence spectroscopy, we measured the fluorescence excitation spectra of the one-exciton 4G5/2(1) ...x 4I9/2(1) state monitored in the near IR, and the two-exciton 4G5/2(1) x 4G5/2(1) state monitored in the near UV of the pair M centers in the Nd3+ doped CaF2 and SrF2 crystals at 6.5 K. We observed the splitting of the one-exciton state of the order of 2–3 cm−1 depending on the type of crystal matrix. A significant inhomogeneous splitting ∼1.5 cm−1 of the spectral lines of the one-exciton state of the pair M centers in the Nd3+: SrF2 crystals was found. The measured single spectral line of the two-exciton state of the pair M centers in these crystals has in one-photon scale the linewidth of ∼0.8 cm−1, which is mainly determined by inhomogeneous broadening.
•Nd3+ ion pairs in CaF2 and SrF2 doped crystals are studied by biharmonic excitation.•Strong resonance exchange interaction splits entangled the4G5/2(1) x 4I9/2(1) state.•Exchange of electron excitation with spin flip results in splitting of several cm−1.•Doubly excited 4G5/2(1) x 4G5/2(1) state has no resonance exchange interaction.•Two Nd3+ pairs in CaF2 and SrF2 crystals can be used as qubits for CNOT quantum gate.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Absorption of twisted photons for quadrupole f4−f4 transitions in Re3+ impurity ions in micro- and macrocrystals is considered. Two types of twisted photon beams-the Laguerre-Gaussian and the ...Bessel-Gaussian beams-are considered and compared. Twisted photons have a nonzero transverse field gradient, which leads to selection rules for quadrupole transitions other than those in the case of the usual quadrupole transitions caused by a longitudinal field gradient. This allows one to observe new spectral lines which are absent in the usual absorption spectra. For microcrystals placed at the beam axis of twisted photons the otherwise dominating forced dipole f4−f4 transitions are absent, which simplifies the observation of new spectral lines.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Earlier, it was shown by the EPR method that at a very low concentration of the Nd3+ ion in the Nd3+:CaF2 crystal, highly symmetric cubic centers with the Oh symmetry are formed. In the present ...study, the optical centers of the Nd3+ ion with an anomalously long radiative lifetime τR = 13.6 ms of the 4F3/2(1) crystal-field (CF) level in the Nd3+ (0.05 at.%): Na+ (0.2 at.%): CaF2 single crystal at T = 7 K were detected by the method of time-resolved site-selective fluorescence laser spectroscopy. Its fluorescence excitation at the 4I9/2(1) → 4G5/2(1) transition of Nd3+ is in a longer wavelength spectral range compared to optical tetragonal (C4v) L-, orthorhombic (Cs) pair M-, and quartet N- centers. New optical centers exhibit inhomogeneous splitting and can be attributed to nearly cubic sites with symmetry close to Oh. Also numerous Nd3+ optical sites in the Nd3+ (0.03 at.%): CaF2 and Nd3+ (0.05 at.%): Na+ (0.2 at.%): CaF2 crystals at T = 7 K with τR = 240 μs ‒ 8.5 ms of the 4F3/2(1) CF level of Nd3+ were detected in a shorter wavelength spectral range compared to the nearly cubic sites. Among them, the sites with the longest τR = 8.5 ms except for the nearly cubic sites, which were identified as C2v symmetry sites. Their radiative lifetime is about six times that of the C4v site (τR = 1.4 ms). This means that, for optical sites without a center of inversion, the radiative lifetime of the excited state at sites with higher symmetry can be almost an order of magnitude less than at sites with lower symmetry. We explained this result by the different distance between the Nd3+ ion and the ion, which compensates for the excess of its charge. Thus, we have demonstrated the use of the Judd-Ofelt approach to explain the difference in the rates of emission of the excited state in different optical sites of the same rare-earth ion in the same crystal matrix.
•We detected fluorescence of Nd3+ nearly cubic sites in the Nd3+:Na+:CaF2 crystal.•The 4F3/2(1) CF level lifetime of Nd3+ of the nearly cubic sites is long, τR = 13.6 ms.•An inhomogeneous splitting of the spectral lines of the nearly cubic sites is found.•τR of the C2v symmetry site is about six times that of the C4v higher symmetry site.•We explained the result by different Nd3+-Na+ distances using the Judd-Ofelt approach.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
To improve methods of laser hyperthermia for the treatment of bulk malignant neoplasms, an urgent task is the development of techniques and devices that automatically control heating at a given ...tissue depth and ensure its uniformity. The article proposes the concept of a system for performing hyperthermia with real-time spectroscopic temperature control and surface cooling, which allows to record spectra of diffusely scattered radiation and fluorescent signal from various depths of biological tissues by the means of the variation of the angle and distance between the fiber source of laser radiation and the receiving fiber. Theoretical and experimental modeling of the spatial distribution of diffusely scattered radiation and temperature inside the tissue with a fiber optic device providing surface cooling of the irradiated tissue, and recording spectral information from a given depth in real time, is presented. Simulation of radiation propagation in biological tissues, depending on the distance between the source and the receiver and the angle of their tilt, was carried out using the Monte Carlo method. Modeling of the temperature distribution inside the tissues was carried out by means of a numerical solution of the heat conduction equation. Experimental modeling was carried out on phantoms of biological tissues simulating their scattering properties as well as accumulation of the investigated nanoparticles doped with Nd
3+
ions. It was shown that inorganic nanoparticles doped with rare-earth Nd
3+
ions can be used as temperature labels for feedback to the therapeutic laser. According to the results of the theoretical simulation, optimal configurations of the relative arrangement of the fibers were chosen, as well as the optimum surface cooling temperatures for the given power densities. The heating of the phantom of the neoplasm containing the investigated nanoparticles doped with Nd
3+
ions by laser radiation with an 805-nm wavelength and power density of 1 W/cm
2
up to 42 °C at a depth of 1 cm while maintaining the surface temperature within the limits of the norm was demonstrated.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
