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arXiv 1109.2250cond-mat.mtrl-sciphysics.optics
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低温法制备Zn(1-x)MgxO纳米晶的结构和光学性质

Structural and Optical properties of Zn(1-x)MgxO nanocrystals obtained by low temperature method

Manoranjan Ghosh, A. K. Raychaudhuri

摘要:

本文报道了用低温法合成的Mg取代的ZnO(Zn_(1-x)Mg_xO)纳米晶(~10- 12 nm)的结构和光学性质。在低温合成路线中,可以达到x = 0.17而没有富Mg相的偏析。通过定量分析确定了准确的化学成分。XRD数据的Rietveld分析证实了纤锌矿结构和随着x增加晶格的连续压实(特别是c轴参数)。随着Mg的替代,晶格中的应变增强。带隙也随着x的增加而增强,并且对于x = 0.17达到4 eV的值。从TEM和XRD数据可以得出结论,当x > 0.17时存在相分离时,在ZnO上存在Mg(OH)2壳。吸收还表明,激发子吸收的持久性Mg取代。该纳米晶在室温下显示出近带边光致发光(PL),其在Mg掺入后显示出蓝移。ZnO和Zn_(1-x)Mg_xO合金纳米晶在~550 nm波长处除了具有近带边发射外,还具有蓝绿色发射。我们发现,绿色发光的相对强度增加与镁浓度为非常低的x(高达x = 0.05)和镁浓度的进一步增加有一个急剧下降的绿色发光的相对强度,最终导致一个完全猝灭的蓝色发光。结果表明,由于相分离(x \geq 0.20),Mg(OH)2在ZnO表面形成的壳层导致了绿光发射的猝灭,但这种壳层的形成对近带边的PL没有太大的影响。

英文摘要:

In this paper we report structural and optical properties of Magnesium substituted Zinc Oxide (Zn1-xMgxO) nanocrystals (~10-12nm) synthesized by low temperature route. In the low temperature synthesis route it was possible to reach x = 0.17 without segregation of Mg rich phase. The exact chemical composition has been established by quantitative analysis. Rietveld analysis of the XRD data confirms the Wurzite structure and a continuous compaction of the lattice (in particular the c-axis parameter) as x increases. There is an enhancement of the strain in the lattice as the Mg is substituted. The bandgap also gets enhanced as x is increased and reaches a value of 4eV for x = 0.17. From the TEM and the XRD data it has been concluded that when there is a phase segregation for x > 0.17, there is a shell of Mg(OH)2 on the ZnO. The absorption also shows persistence of the excitoinc absorption on Mg substitution. The nanocrystals show near band edge photo luminescence (PL) at room temperature which shows blue shift on Mg incorporation. In addition to the near band edge emission the ZnO and Zn1-xMg xO alloy nanocrystals show considerable emission in the blue-green region at wavelength of ~550 nm. We find that the relative intensity of the green emission increases with the Mg concentration for very low x (upto x = 0.05) and on further increase of the Mg concentration there is a sharp decrease of relative intensity of the green emission eventually leading to a complete quenching of blue emission. It is concluded that due to phase segregation (for x \geq 0.20), the formation of the shell of Mg(OH)2 on the ZnO leads to quenching of the green emission .However, this shell formation does not have much effect on the near band edge PL.

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