Lithium Fluoride Single Crystals Research Articles

Sound speed measurements in lithium fluoride single crystals shock compressed to 168 GPa along [100

The shock wave response of [100] lithium fluoride (LiF) single crystals at high stresses is of long-standing interest due to their extensive use as optical windows in dynamic compression experiments. The report of melting in shock-compressed LiF single crystals between 134 and 152 GPa—based on a single sound speed datum [Liu et al., J. Appl. Phys. 117, 045901 (2015)]—was surprising because good optical transmission was previously demonstrated in LiF shock compressed to ∼200 GPa [Rigg et al., J. Appl. Phys. 116, 033515 (2014)]. To address these apparent differences, we report on plate impact experiments on [100] LiF single crystals shock compressed to 168 GPa. Wave profiles were measured using laser interferometry to determine Hugoniot states and longitudinal sound speeds in shock-compressed LiF. The measured Hugoniot states are in good agreement with those measured in previous studies. However, the measured sound speeds presented here show no evidence of melting up to 168 GPa. In particular, the abrupt drop reported previously in sound speed at 152 GPa was not observed in the present work. Our results establish a lower bound of 168 GPa for the onset of melting in shock-compressed LiF single crystals.

Thermal transport and optical spectroscopy in 710-MeV Bi ion irradiated LiF crystals

We present thermal conductivity measurements of lithium fluoride single crystals irradiated by 710 MeV Bi ions at fluences ranging between 1010 and 1013 cm−2. The thermal transport degradation due to irradiation damage was examined across two depths regions, on nanometer and micrometer scales, by picosecond time-domain thermoreflectance and modulated continuum wave thermoreflectance methods, respectively. The proliferation of swift heavy ion-induced structural defects (color centers) was characterized using optical absorption and photoluminescence spectroscopies. Klemens thermal model was applied to correlate the concentrations of color center defects to thermal conductivity reduction in irradiated LiF crystals.

Исследование плазменных колебаний в стеклообразных диэлектриках методом полного внешнего отражения рентгеновских лучей

Glass-like dielectrics are studied by methods of plasmon dispersion and asymmetry of the number of localized electrons in the zone of formation of the total external reflection of x-rays and the excitation of plasma vibrations. Defined by the internal mechanical stress and the associated polarization of the investigated dielectrics. The absence of internal mechanical stress in a single crystal of lithium fluoride was found out, and the observed polarization is caused by a large macroscopic dipole moment in this single crystal

Refractive index of [100] lithium fluoride under shock pressures up to 151 GPa

Single-crystal lithium fluoride(LiF) is a widely used window material in shock wave experiments to maintain the shock stress on the sample surface. It is transparent under shock compression up to ∼200 GPa, allowing the interferometer to record the movement of the monitored surface. However, the interferometer techniques require knowing the accurate refractive index of LiF under shock compression to deduce the true particle velocity. Although the refractive index of LiF under shock compression has long been studied, different experimental results diverge, especially in the high pressure region. Here, we used iron as the standard material to measure the refractive index of [100] LiF up to 151 GPa using two-stage light gas gun. Our results show that for the 1550 nm light, the true particle velocity (utrue) has a linear dependence on the apparent particle velocity (uapp), utrue = 12.26(2.07)m/s + 0.7759(0.0005)uapp, when the apparent particle velocity, uapp > 0.38 km/s.

Theoretical and Experimental Study of Multipactor Discharge on a Dielectric

A review of theoretical and experimental studies of secondary electron emission microwave discharge (multipactor) on a dielectric is presented. The coefficient of microwave power absorption by a single-surface multipactor on a dielectric is found as a function of the incident microwave power and secondary electron emission properties of the dielectric. Results of experimental studies of a single-surface multipactor on a lithium fluoride (LiF) single crystal in a rectangular waveguide are presented and compared with theoretical results. The dependence of the micowave power absorbed by a single-surface multipactor on the incidence angle of microwave radiation is studied numerically and analytically. The influence of the metal waveguide walls on a single-surface multipactor in a parallel-plate waveguide is analyzed. It is shown that, at a sufficiently high microwave intensity, a combined single + double-surface multipactor develops in the region adjacent to the dielectric window.

Evolution of X-ray rocking curves for paratellurite and lithium fluoride crystals under intense ultrasound

Local deformations of the crystal lattice under ultrasonic loading over a wide range of amplitudes have been investigated by means of recording the X-ray rocking curves for paratellurite and lithium fluoride single crystals.

Analysis and experimental verification of neutron-activated LiF as a stable matrix for tritium beta sources

Tritium (3H) has long been considered a useful radioisotope for many purposes due to its low-energy and pure beta decay. However, due to its aggressive migration, solid-state retention of tritium for use as a beta radiation source is challenging. Bulk-level infusion of tritium in a solid is often employed as a solution to effusion and outgassing but limits the beta radiation output due to the use of high-Z materials. This letter presents experimental and simulated analysis regarding the production and efficacy of a low-Z, solid-state tritium beta source. Single-crystal lithium fluoride (LiF) is used as a host matrix for tritium radionuclides, which are generated by the 6Li(n,α)3H reaction when the crystal is exposed to thermal neutron irradiation. The experimental findings present negligible outgassing of tritium from the material, while the simulation results suggest thickness optimization of the LiF/3H beta source. Moreover, the simulation results indicate significantly enhanced beta output efficiency compared to palladium tritide, which is a state-of-the-art tritium host. With proper thickness, the tritium-filled LiF matrix is a stable low energy beta source, which can be easily produced and incorporated into a variety of applications.

Fluorescent detection of single tracks of alpha particles using lithium fluoride crystals

Lithium fluoride single crystals were successfully used for fluorescent imaging of single tracks of alpha particles. This was realized with a standard wide-field fluorescent microscope equipped with a 100× objective. Alpha particles create F2 and F3+ color centers in LiF crystals. The subsequent illumination with the blue light (wavelength around 445nm), excites these centers and produces fluorescence with a broad band peaked at 670nm. The observed tracks of alpha particles have diameter of about 500nm. Focusing of the microscope at different depths in a LiF crystal, enables imaging changes of shape and position of tracks, allowing for visualization of their paths. These encouraging results are the first step towards practical application of LiF as fluorescent nuclear track detectors.

Mechanical response of lithium fluoride under off-principal dynamic shock-ramp loading

Single crystal lithium fluoride (LiF), oriented [100], was shock loaded and subsequently shocklessly compressed in two experiments at the Z Machine. Velocimetry measurements were employed to obtain an impactor velocity, shock transit times, and in-situ particle velocities for LiF samples up to ∼1.8 mm thick. A dual thickness Lagrangian analysis was performed on the in-situ velocimetry data to obtain the mechanical response along the loading path of these experiments. An elastic response was observed on one experiment during initial shockless compression from 100 GPa before yielding. The relatively large thickness differences utilized for the dual sample analyses (up to ∼1.8 mm) combined with a relative timing accuracy of ∼0.2 ns resulted in an uncertainty of less than 1% on density and stress at ∼200 GPa peak loading on one experiment and <4% on peak loading at ∼330 GPa for another. The stress-density analyses from these experiments compare favorably with recent equation of state models for LiF.

Near and Mid-Infrared Emission Characteristics of Er³⁺/Tm³⁺/Ho³⁺-Doped LiYF₄ Single Crystals Excited by Laser Diode.

Yttrium lithium fluoride (LiYF₄) single crystals triply doped with Er³⁺/Tm³⁺/Ho³⁺ are synthesized by a vertical Bridgman method. Absorption spectra, emission spectra, and decay curves are measured to investigate the luminescent properties of the crystals. Compared with Er³⁺ singly doped and Er³⁺/Tm³⁺ and Er³⁺/Ho³⁺ doubly doped LiYF₄ crystals, an intense emission around 2.7 µm can be obtained in the triply doped LiYF4 crystal under excitation of 980 nm laser diode. Meanwhile, the near infrared emission at 1.5 µm from Er³⁺ in the triply doped crystal is effectively reduced. The possible energy transfer processes and the luminescent mechanisms for enhancing emission at 2.7 µm and quenching emission at 1.5 µm in the Er³⁺/Ho³⁺/Tm³⁺ triply doped crystals are proposed. The large energy transfer efficiency of 82.0% and excellent optical transmission indicate that this Er³⁺/Tm³⁺/Ho³⁺ triply doped crystal can be considered as a promising material for a mid- infrared laser at 2.7 µm.

Simultaneous upconversion luminescence and color centers generated by femtosecond laser irradiation of LiF crystals

We report the upconversion luminescence of lithium fluoride single crystals excited by an infrared femtosecond laser at room temperature. The luminescence spectra demonstrate that upconversion luminescence originates from the color center of F3+. The dependence of fluorescence intensity on pump power reveals that a two-photon excitation process dominates the conversion of infrared radiation into visible emission. Simultaneous absorption of two infrared photons is suggested to produce the F3+ center population, which leads to the characteristic visible emission. The results are on the reveal and evaluation of the simultaneous two-photon absorption on the green upconversion process.

Anharmonic thermal oscillations of the electron momentum distribution in lithium fluoride.

Anharmonic thermal effects on the electron momentum distribution of a lithium fluoride single crystal are experimentally measured through high-resolution Compton scattering and theoretically modeled with abinitio simulations, beyond the harmonic approximation to the lattice potential, explicitly accounting for thermal expansion. Directional Compton profiles are measured at two different temperatures, 10 and 300K, with a high momentum space resolution (0.10a.u. in full width at half maximum), using synchrotron radiation. The effect of temperature on measured directional Compton profiles is clearly revealed by oscillations extending almost up to |p|=4 a.u., which perfectly match those predicted from quantum-mechanical simulations. The wave-function-based Hartree-Fock method and three classes of the Kohn-Sham density functional theory (local-density, generalized-gradient, and hybrid approximations) are adopted. The lattice thermal expansion, as described with the quasiharmonic approach, is found to entirely account for the effect of temperature on the electron momentum density within the experimental accuracy.

Rotations of monoblocks of a single crystal in a shock wave front during the measurement of the interplanar spacing by two characteristic radiation lines

The structure of shock-compressed lithium fluoride single crystals has been studied using pulsed X-ray diffraction with Kα and Kβ characteristic radiation lines. The X-ray diffraction patterns of the shock-compressed single crystals indicate that the monoblocks are rotated by ∼3° in the shock-wave front in both the plastic flow region and the elastic region. Ignoring this phenomenon leads to errors in the interpretation of the obtained results.

Efficient Near-Infrared Quantum Cutting in Tm3+/Yb3+ Codoped LiYF4 Single Crystals for Solar Photovoltaic

Downconversion (DC) with emission of two near-infrared photons about 1000 nm for each blue photon absorbed was obtained in thulium (Tm3+) and ytterbium (Yb3+) codoped yttrium lithium fluoride (LiYF4) single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were measured through photoluminescence excitation, emission spectra and decay curves. Luminescence between 960 and 1050 nm from Yb3+: 2F5/2→2F7/2 transition, which was originated from the DC from Tm3+ ions to Yb3+ ions, was observed under the excitation of blue photon at 465 nm. Moreover, the energy transfer processes were studied based on the Inokuti-Hirayama model, and the results indicated that the energy transfer from Tm3+ to Yb3+ was an electric dipole-dipole interaction. The maximum quantum cutting efficiency approached up to 167.5% in LiYF4 single crystal codoped with 0.49mol% Tm3+ and 5.99mol% Yb3+. Application of this crystal has prospects for increasing the energy efficiency of crystalline Si solar cells by photon doubling of the high energy part of the solar spectrum.

Optical and luminescence properties of single crystals of LiF:Cu and LiF:Mg, Cu

Results from spectral studies of the optical and luminescent properties of single crystals of lithium fluoride grown using the Czochralski technique and doped with ions of copper and magnesium, are presented. The effect of heat treatment regimes and the dependence of the concentration of magnesium impurities on the sensitivity of crystals of LiF:Mg, Cu to ionizing radiation are discussed.

Near and mid-IR spectroscopic properties of Er&lt;SUP&gt;3&lt;/SUP&gt;&lt;SUP&gt;+&lt;/SUP&gt; doped and Er&lt;SUP&gt;3&lt;/SUP&gt;&lt;SUP&gt;+&lt;/SUP&gt;/Nd&lt;SUP&gt;3&lt;/SUP&gt;&lt;SUP&gt;+&lt;/SUP&gt; codoped lutetium lithium fluoride single crystal

High quality Er3+/Nd3+ co- doped Lutetium lithium fluoride (LiLuF4) single crystals with a size of 10 mmx90 mm were grown by a Bridgman method. XRD, absorption spectra, and fluorescence spectra of these single crystals were studied. Enhanced mid- IR emission of 2.7m, and weakened up-conversion emission of 550 nm and down-conversion emission of 1.5 mu m emission were observed in Er3+/Nd3+ co-doped LiLuF4 single crystals under an exciting light of 808 nm, as compared with Er3+ singly-doping. Meanwhile, Mid-IR emissions of 3.6 mu m and 4.2 mu m were also observed in Er3+/Nd3+ co-doped LiLuF4 single crystals. Energy transfer efficiencies between Nd3+ and Er3+ ions were calculated and the decay curves of the 1.06 mu m for Nd3+ emission and 1.5 mu m for Er3+ emission were analyzed with a modified Inokuti-Hirayama model. The large energy transfer efficiency of 95.6% and excellent optical properties indicate that this Er3+/Nd3+ co-doped LiLuF4 single crystal is a potential candidate for the applications in mid-IR laser.

Cooperative Down-Conversion Luminescence in $ \hbox{Tb}^{3+}/ \hbox{Yb}^{3+}$ Co-Doped $\hbox{LiYF}_{4}$ Single Crystals

Cooperative down-conversion (DC) with emission of two near-infrared photons for each blue photon absorbed was achieved in Tb3+/Yb3+ co-doped yttrium lithium fluoride single crystals grown by an improved Bridgman method. The luminescent properties of the crystals were investigated through photoluminescence excitation, emission spectra, and decay curves. With the excitation of Tb3+ ion by a 486 nm light, emission between 980 and 1030 nm from the Yb3+:2F5/2 → 2F7/2 transition was observed, and this emission originated from the DC between Tb3+ and Yb3+ ions. The energy transfer processes are studied based on the Inokuti-Hirayama's model, and the interaction between Tb3+ and Yb3+ is confirmed to be electric dipole-dipole. The large quantum cutting efficiency approaches up to 166.7% for 0.32 mol% of Tb3+ and 7.98 mol% of Yb3+ co-doped LiYF4, which is potentially used as a DC layer in silicon-based solar cells.

诊断LiF单晶弹性变形的瞬态X射线衍射

诊断LiF单晶弹性变形的瞬态X射线衍射

磁驱动准等熵压缩下单晶氟化锂的光学特性

磁驱动准等熵压缩下单晶氟化锂的光学特性

Synthesis and efficient near-infrared quantum cutting of Pr3+/Yb3+ co-doped LiYF4 single crystals

Yttrium lithium fluoride single crystals doped with trivalent lanthanide ions Pr3+ and Yb3+ are prepared by an improved Bridgman method. X-ray diffraction, photoluminescence excitation, and emission spectra and decay curves are measured to investigate the structural and luminescent properties of the crystals. An efficient near-infrared quantum cutting downconversion from the crystals was observed. The downconversion involves the emission of two near-infrared photons for each blue photon absorbed at 480 nm via cross relaxation energy transfer from Pr3+ to Yb3+. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. The maximum quantum cutting efficiency approaches up to 168.4% in LiYF4: 0.28 mol. % Pr3+ and 6.02 mol. % Yb3+, and this is equivalent to 68.4% energy transfer efficiency.