The radiative and nonradiative transitions of the first three excited levels of Er3+ doped in Ga2S3–GeS2–Sb2S3 glass were investigated. Particularly, we focused on the 4I9/2 and 4I11/2 which are the initial and final levels of mid‐infrared emission around 4 µm. The effects of energy transfer from these levels to co‐doped rare‐earth ions, Yb3+ and Nd3+, were estimated. The population of the final level, 4I11/2, was efficiently quenched by the energy transfer to the Yb3+, 2F5/2 level. This leads to the population inversion between the initial and final levels. In the Nd3+‐co‐doped glass, on the contrary, the initial level, 4I9/2, was more rapidly quenched than the final level, 4I11/2, through the energy transfer to Nd3+, 4F5/2 + 2H9/2. 相似文献
Various resonators for surface emission are reviewed that have recently been developed to improve radiative‐ and collection‐efficiencies of terahertz quantum cascade lasers (THz QCL). While the fabrication of waveguides for long wavelengths is challenging in terms of molecular beam epitaxy, long wavelengths also provide a wonderful testbed for new photonics structure concepts, since these can be easily produced by conventional optical lithography because of the typically large size of the required features. This led to novel geometries, like one‐ and two‐dimensional non‐periodic photonic crystals, or circular gratings for microdisk‐ and ring‐lasers, which are all implemented by simply patterning the top metal cladding of a metal‐metal waveguide. The modeling of such resonators with the finite element method is also described, highlighting the importance of this tool for the engineering of surface losses and far‐field patterns. 相似文献
Coiled carbon nanostructure (CNS) is prepared by a catalytic chemical vapor deposition (CVD) process on copper/chromium films deposited by radio frequency (RF) sputtering. Uniform CNS with coiled structure is fabricated by changing the size of the catalyst particles. The effects of Cu catalyst size and RF sputtering power, on the growth of the coiled CNS are discussed, and the results importantly conclude that Cu-catalyzed CVD offers a preferable control of coiled CNS to optimize the field emission property for application. 相似文献
It remains a challenge to generate cold, atmospheric pressure plasmas in sealed packages for biological disinfection. In this paper, we report a plasma device to form large‐area and atmospheric‐pressure plasmas in a sealed package for the low‐temperature disinfection of fungi. The visually uniform plasmas were easily generated in the portable plastic bag containing Candida albicans with a population of 105 spores placed on the plasma device. The He plasma containing about 1% O2 was found to entirely kill resistant Candida albicans with a treatment time of 5 min. Measurements for optical emission spectra and disinfection efficiencies indicate that the plasma‐created species such as O radicals and charged species play a major role in the inactivation process.
The field emission properties of gallium oxide nanowires grown by thermal evaporation–deposition have been investigated inside the chamber of a scanning electron microscope. Turn on electric fields and enhancement factors have been determined for Sn doped nanowires. X‐ray photoelectron spectroscopy measurements have been performed to calculate the work function of Sn doped Ga2O3. The results show improved field emission properties of Sn doped Ga2O3 nanowires, with a lower threshold field (below 1.0 V/µm). The obtained values are competitive with those achieved in other nanostructured materials, including carbon nanotubes. 相似文献
Dy3+ doped lead fluoroborate (LFB) glasses (B2O3 + PbO + PbF2) have been prepared following conventional melt quenching technique by varying the concentration of Dy2O3 in the order 0.01, 0.1, 1, 2, and 3 mol%. X‐ray powder diffraction (XRD), Fourier transform infrared (FTIR), optical absorption, fluorescence emission, and decay curves have been recorded and analyzed. From the optical measurements and based on the Judd–Ofelt (JO) theory, the JO intensity parameters were evaluated and in turn used to evaluate the radiative transition probabilities (A), stimulated emission cross‐section ( ), radiative lifetimes (τrad), and branching ratios (βR) for the various 4F9/2 → 6HJ (J = 11/2, 13/2, 15/2) transitions of Dy3+ ions in the LFB glasses and these values were compared with the other reported Dy3+:glasses. The decay curves of the 4F9/2 level were measured and found to be deviate from the exponential nature with the increase in Dy3+ ion concentration. The luminescence quantum efficiency of the 4F9/2 level was also determined and discussed. Differential scanning calorimetry (DSC) curves were used to evaluate the glass stability factor (S) and Hruby's parameter (HR) through the glass transition (Tg), crystallization (Tc), and melting (Tm) temperatures and these results were discussed and reported. 相似文献
A boron‐doped polycrystalline diamond film was deposited on a molybdenum substrate and resistively heated in a high vacuum environment. The thermally excited emission current as a function of cathode temperature was measured. This phenomenon, known as thermionic emission, is characterized by electron emission arising from a surface at elevated temperatures and is described by the Richardson equation. The observed thermionic emission current from the diamond sample followed the Richardson equation from which a work function of 4.43 eV and a Richardson constant of ∼60 A/cm2K2 were observed. This indicates boron‐doped polycrystalline diamond behaves as an interesting thermionic emitter for possible energy conversion and other electron emission applications. 相似文献
In this report, the current–voltage (I–V) characteristics of Au/GaN Schottky diodes have been carried out in the temperature range of 300–510 K. The estimated values of the Schottky‐barrier height (SBH) and the ideality factor of the diodes based on the thermionic emission (TE) mechanism were found to be temperature dependent. The barrier height was found to increase and the ideality factor to decrease with increasing temperature. The conventional Richardson plot of ln(Is/T2) versus 1/kT gives the SBH of 0.51 eV and Richardson constant value of 3.23 × 10−5 A cm−2 K−2 which is much lower than the known value of 26.4 A cm−2 K−2 for GaN. Such discrepancies of the SBH and Richardson constant value were attributed to the existence of barrier‐height inhomogeneities at the Au/GaN interface. The modified Richardson plot of ln(Is/T2)–q2σ/2k2T2 versus q/kT, by assuming a Gaussian distribution of barrier heights at the Au/GaN interface, provided the SBH of 1.47 eV and Richardson constant value of 38.8 A cm−2 K−2. The temperature dependence of the barrier height is interpreted on the basis of existence of the Gaussian distribution of the barrier heights due to the barrier‐height inhomogeneities at the Au/GaN interface. 相似文献
