Chemical modification can effectively control the quantum spin Hall (QSH) state by changing the lattice constant or topological phase transition. We functionalized ultraflat stanene with hydrogen and halogens on a single side (s-SnX) and both sides (b-SnX). It was found that the buckled heights of the neighboring Sn atoms for s-SnX were still zero, while b-SnX changed into a buckled structure, which is consistent with previous studies. In this work, the electronic and topological properties of s-SnX (X = H, F, Cl, Br, I) were mainly studied based on first-principles calculations. We predicted that s-SnF, s-SnCl and s-SnBr would be topological insulators (TIs). It was found that the band structures of s-SnF, s-SnCl, s-SnBr have s-p band inversions and semimetal-to-semiconductor transitions considering spin orbit coupling (SOC) with the largest band gap of 0.25 eV. The edge bands of calculating the edge states cross linearly, and the numbers of edge bands passing through the zero energy level between -X and Gamma point are odd, indicating that s-SnF, s-SnCl and s-SnBr are TIs. Ultraflat stanene functionalized by hydrogen and halogen atoms can effectively control QSH states. It is proved that functionalization provides more choices for topological insulator materials and topological device applications.

The results of liquid nitrogen cooling (LNT, 77 K) on the spectral properties of bismuth-doped aluminosilicate fibers (BDFs) have been presented under varying pump wavelengths. It is revealed that the spectral luminescence of bismuth active centers (BACs) is mildly affected upon excitation at 405, 532, and 980 nm at LNT, whereas notable luminescence enhancement (similar to 1.3 times) is observed in the range of 1100-1350 nm (BACs-Al) under 830 nm pumping. The experimental data on the luminescence shape and kinetics of BACs-Al have been obtained at both room temperature (RT) and LNT with varied pumping powers. It is revealed that the enhanced luminescence is caused by the steep rise of emission around 1300 nm (denoted as BAC-Al (II)), which is more efficiently stimulated at a lower temperature. The key laser parameters of BACs have also been evaluated at both RT and LNT. The obtained results may shed some light on the NIR-emitting nature of BACs, and provide a promising strategy for tuning the spectral NIR luminescence scheme of BDFs.

宽禁带半导体具有高效的光电转化能力、优良的高频功率特性、高温性能稳定和低能量损耗等优势,成为支撑信息、能源、交通、先进制造、国防等领域发展的重点新材料。Ga203是一种极具潜在应用前景的宽带隙半导体,其出色的材料特性包括极宽的带隙（Eg～4.9 eV）和高击穿电场（8 MV/cm）,使它特别适用于太阳能盲光电探测器（SBPD）和高功率场效应晶体管（FET）。本论文依托课题组承担的国家自然科学基金（批准号:11547039,61675032）,主要开展了以下几个方面研究工作:1)二维β-Ga203基本物理性质研究。基于准粒子近似+随机相位近似（GW+RPA）和准粒子近似+双粒子格林函数运动方程（GW+BSE）两种方法研究了二维β-Ga203的几何结构、电子结构、光学性质以及激子特性。几何优化的结果显示二维β-Ga203的晶体结构发生了畸变,晶体的对称性下降,并且影响到了它们的电子结构。二维β-Ga203的激子效应非常明显,主导了它们的光学性质。2)H-β-Ga203基本物理性质研究。基于GW+RPA和GW+BSE两种方法研究了H钝化对二维β-Ga203的调控效应,精确地得到了激子束缚能、最大吸收系数以及所对应的能量值。H钝化将影响二维β-Ga203的几何结构、电子结构,且随层数的变化而变化。钝化后材料更加趋向于绝缘性。从基于GW+BSE计算的吸收系数来看,1L、2L、3L在xx、zz三个极化方向上的吸收系数都在105 cm-1数量级,并且GW+BSE方法计算的吸收峰相对于GW+RPA计算的吸收峰发生了明显的红移,在基本电子能带带隙以下的能量范围出现了吸收峰,这说明H-β-Ga203具有很强的激子效应。3)体相β-Ga203以及掺杂Si后β-Ga203基本物理性质研究。准确做出了体相β-Ga203的第一布里渊区、布里渊区高对称点及高对称点路径。基于GW0方法修正了能带带隙（4.67 eV）以及态密度。计算了在r点能带的电子有效质量,它们几乎是各向同性的,其值在0.27 me和0.28 me之间。研究表明,体相β-Ga203材料中的激子效应非常明显,主导了它的光学性质。计算了激子束缚能,及最大吸收峰位置与强度。Si重掺杂后,β-Ga203变为间接带隙材料,其动态介电函数具有各向异性,吸收带边缘上升得更慢。本论文的主要创新如下:（1）采用基于GW近似的多体微扰理论对体相、二维β-Ga2O3展开研究。对体相β-Ga2O3、二维纳米结构β-Ga2O3以及加氢钝化的二维β-Ga2O3的能带结构进行GW0修正计算,分别得到它们准确的能带结构、带隙、态密度以及电子、空穴有效质量等。（2）在准确预测电子结构的基础之上,基于GW+BSE方法对体相、二维β-Ga2O3展开研究。计算了体相β-Ga2O3、二维纳米结构β-Ga2O3以及加氢钝化的二维β-Ga2O3光学性质及激子效应,为基于β-Ga2O3制作光电子器件提供了良好的理论支撑。

The effect of the lead or erbium co-doping upon the spectroscopic properties has been systematically investigated through the analysis of the absorption and emission spectra of Bi doped fibre (BDF), Bi/Pb and Bi/Er co-doped fibre (BPDF and BEDF). All these BDFs have a broadband emission from 1000 nm to 1600 nm. The Pb or Er co-doping in BDFs will evidently reduce the formation of bismuth related active centres (BACs) due to the formation of other types' centres and then restrain the emission of BAC through their competition of the pump consumption and the cross energy transfer among these active centres. Further analysis indicates that the co-doping effect of Pb to restrain the formation of BAC and its emission is stronger than that of Er to some degree, possibly due to the analogy property between Bin+ and Pbn+ with isoelectronic configures. In addition, the analysis of the BAC concentration indicates that the atom concentration measured by energy dispersive X-ray (EDX) analyser has a large gap with the effective content reflected from the absorption and emission. All these results point out a way to design and fabricate bismuth doped/co-doped fibre with high performance in future.

We investigated the thermal-related spectral properties for BEDF under 830 nm pumping and observed a notable (similar to 1.6 times) luminescence enhancement in the range of 1.1-1.3 mu m by thermal quenching at 500 degrees C. (C) 2020 The Author(s)

The first results of the liquid nitrogen cooling effect on the spectral properties of a phosphor-related bismuth active center (BAC-P) have been presented. It is found that the small-signal absorption bands of BACs are mildly affected at liquid nitrogen temperature (LNT, 77 K), while the unsaturable absorption level is lowered moderately. Meanwhile, noticeable shape changes of luminescence spectra and enhanced luminescence intensity (∼ twice) of BAC bands were revealed at LNT upon excitation at 830 or 980 nm, which is contributed by the notable growth of BAC-P. In addition, the influence of cooling on the on-off gain performance of BACs is also explored. Furthermore, the laser-induced effect on the luminescence of BAC-P upon cooling at LNT is also investigated, revealing a noticeable increase (∼10%) instead of photobleaching. These experimental results bring new insights into the temperature-related spectral properties of BACs and provide an effective way for tuning the luminescence scheme for Bi-doped fibers by cryogenics for the desired spectral range 1.26–1.36 µm.
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