Infrared absorption of OH- doped LiF

The low temperature IR spectra of OH^- doped LiF shows no additional absorption in the vicinity of the main stretching band. This suggests that it is an “on-center” paraelectric system and that this feature suppresses most manifestations of this type of impurities.     

UV luminescence from LiF/carbon nanotube microcomposites

In this work we perform a study on growth and characterization of LiF/carbon nanotube (CNT) composites.     

Spin-lattice relaxation of the Vk-center in LiF

The angular and temperature dependences of the spin-lattice relaxation (SLR) rate of V_k-centers in LiF doped with Mg or Ag have been investigated. In the temperature interval 4.2–100 K the results can be fitted by the formula $\text{τ}{}^{\mathrm{?1}}\text{= A(θ)T + Be}{}^{\mathrm{<mtext>?\Delta </mtext><mtext>T</mtext>}}$ with A(0°) = 0.11 sec^?1K^?1, A(90°) = 1.3 sec^?1K^?1, B = 3 × 10⁵sec^?1 and Δ = (175 ± 15)K.A mechanism for the SLR is considered, assuming the modulation of the hyperfine interaction by phononinduced transitions between the ground and excited states of the resonant molecular vibrations of the V_k-center. This mechanism is found to explain the value, the temperature dependence and the isotropy of τ^?1 in the interval T = 20–100 K.The one-phonon SLR mechanisms of the V_k-center in the T < 10 K region are discussed.     

Proton-induced F-centers in LiF and MgF2

The growth of F-centers in LiF irradiated at room temperature with 40- and 85-MeV protons and with ⁹⁰Sr electrons was found to be proportional to the square root of the absorbed energy over the range 0.5 to 2.3 Mrad which corresponds to an F-center density range of 1 × 10¹⁶ to 1.5 × 10¹⁷ per cm³. The production efficiency was 5 × 10³eV per F-center at an absorbed energy of 2.3 Mrad. The density of F-centers produced in MgF₂ by 40- and 85-MeV protons was measured over an absorbed energy range of 0.2 to 29 Mrad which corresponds to a maximum F-center density of 2 × 10¹⁶ per cm³. The production efficiency for MgF₂ was 4 × 10⁵eV per F-center at an absorbed energy of 16 Mrad.     

利用LiF/Al作为电极的有机电致发光器件

本文报道了利用LiF/Al作为负电极的有机电致发光器件,器件结构为ITO/TPD/Alq3/LiF/Al,LiF层的加入增强了电子注入,当其厚度为0.4nm时,器件的性能最好,与单层Al和Mg/Al电极的同类器件相比,此时器件的开启电压由Al电极时的4.3V和Mg/Al电极时的3.0V降低到了2.0V,器件的最大亮度分别由4000cd/m²、14000cd/m²提高到19600cd/m²,器件的发光效率也分别增加了5倍和2倍,达到2.66lm/W.     

Y-Absorptionsbande im bestrahlten LiF

The absorption measurements at a constant and uniformly increasing temperature and the thermostimulated electron emission and luminescence of with α-, cathode- andγ-rays irradiated LiF crystals were performed and the conditions of the formation of a new absorption band at about 500 nm investigated. It turned out that the band in α-irradiated samples is composed from two and inγ-irradiated from three bands. In this case the short-wave-length-band with the zero-phonon-line at 491 nm is very probably the well knownF ₃ ^t -band. The long-wave-length-band with the zero-phononline at 507 nm (theX band) is of unknown nature. TheY band lies at 494,3 nm (at 77 ?K) and its nature could consist in the colour centre agglomerates.     

Blocking of interfacial diffusion at Ag/Alq3 by LiF

X-ray photoelectron spectroscopy has been applied to interface studies of Ag/tris-(8-hydroxyquinoline) aluminum (Alq₃) and Ag/LiF/Alq₃. For Ag/Alq₃, diffusion of Ag atoms into the Alq₃ layer occurs immediately after the adhesion of the metal onto the organic layer and the process lasts several hours. Insertion of a monolayer-thick LiF buffer at the interface can effectively block the diffusion process. This is quite different from what is observed from Al/LiF/Alq₃, where Al penetrates into the LiF layer as deep as several nanometers. It is thus concluded that the LiF buffer may play different roles in Ag/LiF/Alq₃ and Al/LiF/Alq₃ and hence different mechanisms may dominate in the two cases for the enhanced carrier injection observed.     

LiF:F+2-centre laser for intracavity spectroscopy

We describe a broad-band uncooled LiF:F⁺₂ colour centre laser (880–970 nm), pumped by a pulsed Xe-ion laser, for intracavity spectroscopy. Spectra of molecular absorption and gain, and of time-resolved absorption by atomic metastables demonstrate the versatility of the system.     

Electroluminescence efficiency in bilayer organic light-emitting devices with LiF/Al cathode

An analytical model to calculate electroluminescence (EL) efficiency of bilayer organic light-emitting devices, considering the influence of introducing LiF insulating buffer layer at metal/organic interface on the barrier height for electron injection, was presented. The relations of EL efficiency versus the applied voltage and injection barrier or internal interfacial barrier or the thickness of organic layer were discussed. The results indicate that: (1) when δ e/δ h < 2, metal/organic (M/O) interface is ohmic contact; when δ e/δ h > 2, M/O becomes contact limited; and when δ e/δ h = 2 (Φ h ～ 0.2 eV, Φ e ～ 0.3 eV), there is a transition from ohmic contact to contact limited; (2) η EL decreases with the increase of δ′e / δ′h; however, when δ′e / δ′h > 2.5 (H ′h～ 0.2 eV, H ′e～ 0.4 eV), the changes of η EL are very small, which shows that η EL is dominated by the carrier’s injection; (3) when increasing Lh/L, η R has a descending trend at low voltage and a rising one at higher voltage. For a given Lh/L, η EL first increases and then decreases with the increasing applied voltage, and as Lh/L further increases, the variation tendency of η EL is more obvious. These conclusions are in agreement with the reported theoretic and experimental results.     

Enhanced electron injection in organic light-emitting devices using Al/LiF electrodes

The temperature dependence of the current-voltage-luminescence characteristics in organic light-emitting diodes (OLEDs) with varying thickness of LiF layers are studied to understand the mechanism of the enhanced electron injection by inserting a thin insulating LiF layer at the tris(8-hydroxyquinoline) aluminum (Alq₃)–Al interfaces. At room temperature, the LiF/Al cathode enhances the electron injection and the quantum efficiency (QE) of the electroluminescence (EL), implying that the LiF thin layer lowers the electron-injection barrier. However, at low temperatures it is observed that the injection-limited current dominates and the barrier height for the electron injection in the device with LiF/Al appears to be similar with the Al only device. Thus, our results suggest that at low temperatures the insertion of LiF does not cause a significant band bending of Alq₃ or reduction of the Al work function.     

Intraband radioluminescence of LiF crystals

Spectra of high-energy electrons are calculated in the electron-hole ionization-passive region of lithium fluoride crystals for the conditions of intense irradiation by short pulses of accelerated electrons. The yield of intraband radioluminescence of these crystals is estimated in comparison with the yield of this kind of luminescence of more extensively studied NaCl crystals. The calculations demonstrate that the yield of radioluminescence determined by electron transitions in the conduction band of LiF crystals is two orders of magnitude weaker than the yield of analogous luminescence of NaCl crystals. This is explained, first, by special features of the energy band structure and, second, by the form of the energy dependence of the density of states in the conduction band of LiF crystals. The yield of hole-type intraband radioluminescence is estimated for various assumed relations between the widths of the valence and the forbidden bands.     

Core-exciton phonon interaction in LiF

The temperature coefficients of the fundamental exciton at 12.6 eV and the Li⁺1s-2p exciton at 61.9 eV in LiF are both negative. But the Li⁺ core exciton should have a small positive temperature coefficient or, more likely, a zero one according to the point-ion model. We checked the validity of the point-ion model for LiF by measuring with great accuracy the temperature dependence of core levels binding energies by means of x-ray photoemission spectroscopy. We have concluded that the Li⁺1s-2p exciton temperature coefficient arises entirely from exciton-phonon interaction. We have determined also the Li⁺1s absorption threshold from available thermo-absorption spectra. The core-exciton phonon interaction is discussed using different models.     

Linearer Stark-Effekt desR-Zentrums in LiF

The K-ionization cross section of Aluminium by electron impact was measured detecting quantitatively the Al-K X-rays emitted by thin targets of known mass thickness. The apparatus and the measurements are briefly described. The experimental results are considerably higher than the values of the theories using the Born approximation. The discrepancy increases with increasing energy of the incoming electron. At twenty-fold threshold energy for example, the measurements are higher thanBurhop's calculations by a factor of 1.7. It is shown that considering the process ofK-ionization the influence of the nuclear field on the impact electron increases with decreasing atomic number. Thus, the calculations ofRudge andSchwartz using coulomb wave functions for the impact electron, are closest to the measurements (maximum deviation 16%). The formula ofGryzinski based on classical calculations is a good approximation to the experimental results if multiplied by a factor 1.23.     

Investigation and simulation of the structural and electronic properties of LiF:Mg,LiF:Cu,LiF:P nano-layer dosimeters

In this study, electronic structure of lithium fluoride thin films in pure state and doped with magnesium (Mg), copper (Cu) and phosphorus (P) impurities was studied using WIEN2K Code. The structural and electronic properties of two LiF thin films with 1.61 and 4.05?nm thicknesses were studied and compared. Results show that the distance of atoms in the surface and central layers of pure LiF are 1.975 and 2.03?nm, respectively. Electronic density of the valence band around the surface atoms is greater than that around middle atoms of the supercell. The band gap of bulk LiF is 9?eV. But, in the case of thin films, it is reduced to 2?eV. Electronic and hole-traps were not observed in composition of LiF thin films doped with Mg and P with 1.61 and 4.05?nm thickness and in fact, metallic properties were observed. When Cu atoms were doped in composition of an LiF thin film, the thin film was converted to semiconductor.     

A new phase growth in LiF: Ti and LiF: Ti,Mg

Abstract

ITC measurements, optical absorption spectra in the wavenumber range 5.4 × 10⁴?200 cm^?1, microspectrophotometry, photoluminescence spectra, optical and electron microscopy and X-ray diffraction have been used to study the growth and the nature of a new phase occlusions in LiF: Ti³⁺ and LiF: Mg²⁺, Ti³⁺. They grow along the 100 direction as a consequence of high temperature heat treatments in moist atmosphere.     

Ultraviolet photoemission study of LiF

Photoemission from evaporated films of LiF were measured at photon energies of 10-27 eV. The photoelectron spectra exhibit features that can be identified as density-of-states structures in the valence and conduction bands of LiF. Regions of high density of states can be seen at ca. 3.3 and 7.8 eV above the vacuum level. The valence-band spectrum shows a doublet structure similar to the calculated density of states for the F^?2p band of LiF. The base width of this structure is found to be 4.6 ± 0.3 eV. The photoelectron spectra for photon energies > 15 eV indicate that the highest occupied states of the F^?2p band are located at 11.8 ± 0.3 eV below the vacuum level. The photoelectron spectra in the exciton region, however, show photo-emission from higher occupied states.     

用作VISAR窗口的LiF晶体折射率变化修正因子

 利用加窗VISAR测速方程和平面碰撞实验产生已知样品-窗口界面粒子速度的方法，对LiF晶体用作VISAR（激光波长532 nm）测速窗口时的折射率变化修正因子进行了测定。给出了LiF晶体窗口在冲击压力2.7~66 GPa范围内，折射率变化修正因子测量结果及界面粒子速度修正方法。     

Impurity cathodoluminescence of oxygen-containing LiF crystals

Cathodoluminescence of oxygen-containing LiF crystals (LiF-O, LiF-O,OH, LiF-WO₃) is studied by pulsed spectrometry with nanosecond resolution upon excitation of crystals by a single electronbeam pulse at 15 K.     

Photoluminescence measurements of LiF TL detectors

The properties of standard lithium fluoride (LiF) thermoluminescent (TL) detectors, which are routinely used in radiation protection systems, were investigated under light stimulation. The luminescence of different types of LiF detectors, which were irradiated with gamma rays of energy up to 300 Gy and alpha particles with a fluence up to 5*10⁹ cm⁻², were stimulated by a blue light and were heated up to temperature of 240 °C or 400 °C, depending on the type of detectors. The irradiated LiF detectors during the blue-light (460 nm) stimulation emit green photoluminescence (PL) with a wavelength of 530 nm. The LiF detectors showed a PL effect of much higher efficiency after they were irradiated with alpha particles than after they were irradiated with gamma rays. However, in contrast to PL, the TL readout showed a significantly lower efficiency of LiF detectors after alpha particle irradiation. These effects result from the different trap mechanisms that are responsible for TL and PL phenomena. The temperature stability of the traps responsible for the PL effect for both types of LiF detectors was studied.