RESUMEN
The effect of the difference in the thickness ratio of the double-layered thickness-shear resonator on the temperature characteristics of the resonance frequency was investigated using a Ca3TaGa3Si2O14 (CTGS) single crystal. Three specimens with thickness ratios of x = 0.25 , 0.33, and 0.50 were prepared using 122° Y - and 171° Y -cut CTGS substrates. For the specimens with x = 0.25 and 0.33, the temperature characteristics varied depending on the order of the resonance mode. For the specimen with x = 0.50 , on the other hand, almost the same temperature characteristics were observed regardless of the order of the resonance mode. To interpret this phenomenon, a new equation for predicting the temperature characteristics of the fundamental mode (first mode) for the double-layered resonator was created using the electric flux density ratio generated in the two substrates. The expected values using this equation were in good agreement with the result of the first mode temperature characteristics.
Asunto(s)
Vibración , TemperaturaRESUMEN
We report on the potential of the potassium magnesium fluoride (KMgF) crystal as a fast-response scintillator with tunable cross-luminescence (CL) emission wavelength through high-pressure applications. By performing first-principles density functional theory calculations using the Perdew-Burke-Ernzerhof (PBE) hybrid functional including exact exchange (PBE0) and Green's function and screened Coulomb interaction approximation as implemented in the Vienna Ab initio Simulation Package using plane-wave basis sets within the projector-augmented wave method, we identify the specific valence-to-core band transition that results in the experimentally observed CL emission at 148 nm (8.38 eV) and 170 nm (7.29 eV) wavelengths with intrinsically fast decay times of 290 ps and 210 ps, respectively. Uniform volume compression through hydrostatic high-pressure applications could decrease the energy gap between the valence and core bands, potentially shifting the CL emission wavelength to the ultraviolet (UV) region from 200 nm (6.2 eV) to 300 nm (4.1 eV). The ability to tune and shift the CL emission to UV wavelengths allows for the detection of the CL emission using UV-sensitive photodetectors in ambient atmosphere instead of highly specialized vacuum UV detectors operating in vacuum while maintaining the intrinsically fast CL decay times, thereby opening up new possibilities for KMgF as a fast-response scintillator.
RESUMEN
We propose a scheme for imaging mid-infrared (MIR) wavelengths via pre-excitation-assisted up-conversion luminescence in lanthanide ion (Ln3+)-doped Self-organizing Optical FIber Array (SOFIA) crystal. First, near-infrared pre-excitation wavelength excites an electron from the ground state to an excited state of Ln3+. Next, the MIR wavelength to be imaged promotes this excited electron to a higher-lying energy state. Finally, relaxation of the electron from the higher-lying energy state to the ground state emits the up-conversion luminescence in the visible region, completing the MIR-to-visible wavelength conversion. An analysis of the 4f to 4f intra-configurational energy level transitions in Ln3+, together with an appropriate selection of the pre-excitation wavelength and the visible luminescence constrained within the 500-700 nm wavelength range, reveals that trivalent erbium (Er3+), thulium (Tm3+), holmium (Ho3+), and neodymium (Nd3+) can be used to image MIR wavelengths. Our proposed scheme, called MIR imAging through up-Conversion LuminEscence in a SOFIA crystal, will enable the imaging of MIR wavelengths using low-cost optics and readily available silicon-based detectors in the visible spectral region and will open up new possibilities for MIR wavelength detection and imaging.
RESUMEN
We fabricated nanosized KMgF3 single crystals via a dry pulsed laser ablation process using femtosecond laser pulses. The sizes, shapes, and crystallographic properties of the crystals were evaluated by transmission electron microscopy (TEM). Almost all of the particles were spherical with diameters of less than 100 nm, and they were not highly agglomerated. Selected-area electron diffraction and high-resolution TEM analyses showed that the particles were single crystals. Particle diameter was controlled within a wide range by adjusting the Ar ambient gas pressure. Under low gas pressures (1 and 10 Pa), relatively small particles (primarily 10 nm or less) were observed with a high number density. With increasing pressure, the mean diameter increased and the number density drastically decreased. Vacuum-ultraviolet cathodoluminescence was observed at 140-230 nm with blue shift and broadening of spectrum.
RESUMEN
Acoustically related physical constants were experimentally determined for Ca3Nb(Ga0.75Al0.25)3Si2O14 (CNGAS) single crystal for the first time. Several plate specimens of the X-, Y -, Z -, 40.24 ° Y -, and 144.98 ° Y -cut were prepared from a CNGAS single crystal ingot grown by Czochralski technique. Elastic constants, piezoelectric constants, and their temperature coefficients for CNGAS were determined from longitudinal wave and shear wave velocities at around room temperature, measured by the ultrasonic microspectroscopy system. Dielectric constants, density, and coefficients of thermal expansion were also measured. It was demonstrated that the determined constants could provide calculation accuracy within ±0.12% in leaky surface acoustic wave velocity. The piezoelectric constants for CNGAS were a 7.2% increase in e11 and a 1.7% decrease in e14 due to Al-substitution effect, compared with those of Ca3NbGa3Si2O14. The appropriate cut angle for thickness-shear mode resonator with zero temperature coefficient of velocity was estimated to be around 150 ° Y -cut from calculations using the determined constants of CNGAS exhibiting electromechanical coupling factor k2 of 3.19% and power flow angle of -1.70°.
RESUMEN
Ca3Nb(Ga1-xAlx)3Si2O14 (CNGAS) single crystals with various Al concentrations were grown by a micro-pulling-down (µ-PD) method and their crystal structures, chemical compositions, crystallinities were investigated. CNGAS crystals with x = 0.2, 0.4 and 0.6 indicated a single phase of langasite-type structure without any secondary phases. In contrast, the crystals with x = 0.8 and 1 included some secondary phases in addition to the langasite-type phase. Lattice parameters, a- and c-axes lengths, of the langasite-type phase systematically decreased with an increase of Al concentration. The results of chemical composition analysis revealed that the actual Al concentrations in as-grown crystals were almost consistent with the nominal compositions. In addition, there was no large segregation of each cation along the growth direction.
RESUMEN
A vacuum ultraviolet (VUV) field emission lamp was developed by using a neodymium ion doped lutetium fluoride (Nd(3+) : LuF3) thin film as solid-state phosphor and carbon nanofiber field electron emitters. The thin film was synthesized by pulsed laser deposition and incorporated into the lamp. The cathodoluminescence spectra of the lamp showed multiple emission peaks at 180, 225, and 255 nm. These emission spectra were in good agreement with the spectra reported for the Nd(3+) : LuF3 crystal. Moreover, application of an acceleration voltage effectively increased the emission intensity. These results contribute to the performance enhancement of the lamp operating in the VUV region.
Asunto(s)
Electrones , Lutecio/química , Neodimio/química , Humanos , Mediciones Luminiscentes , Rayos UltravioletaRESUMEN
We grew column-shaped Sr(3)NbGa(3)Si(2)O(14) (SNGS) and Sr(3)TaGa(3)Si(2)O(14) (STGS) langasite-type piezoelectric single crystals by the micro-pulling-down (µ-PD) method. 3-mm-diameter SNGS and STGS crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die. According to X-ray rocking curve measurements, the grown crystals had crystallinity equivalent to that of crystals grown by the Czochralski (Cz) method. The crystals were single-phase materials with langasite-type crystal structure. The lattice parameters of the grown crystals were almost consistent with those of crystals grown by the Cz method.
RESUMEN
We have grown shape-controlled langasite-type crystals by the micro-pulling-down (µ-PD) method. Columnar shaped La(3)Ta(0.5)Ga(5.5)O(14) (LTG), Ca(3)NbGa(3)Si(2)O(14) (CNGS), Ca(3)TaGa(3)Si(2)O(14) (CTGS), Sr(3)NbGa(3)Si(2)O(14) (SNGS), and Sr(3)Ta- Ga(3)Si(2)O(14) (STGS) crystals were grown using a Pt-Rh crucible with a 3-mm-diameter columnar die at the bottom. All grown crystals showed high transparency except for the peripheral area and diameter of approximately 3 mm. The chemical phases at the central parts of the grown crystals were identified as a single phase of langasite-type structure and their lattice parameters were almost the same as those of crystals grown by the Czochralski (Cz) method; however, some impurity phases were observed in the peripheral area. In X-ray rocking curve measurements, the grown crystals indicated equivalent crystallinity to the crystal grown by the Cz method. The piezoelectric constant d(11) of the CNGS crystal was 3.98 pC/N; this value is well correlated with those of previous reports.
