掺钴纳米玻璃陶瓷的光谱性质

采用溶胶-凝胶法分别制备和表征了组分为5ZnO(5MgO,5Li2O)-6Al2O3-89SiO2-0.4CoO的掺钴硅酸铝锌(镁,锂)纳米玻璃陶瓷材料.这3种玻璃陶瓷的结晶温度分别为900,1 000℃和850℃,对应的结晶相分别为:ZnAl2O4,MgAl2O4和β-锂辉石、方石英,晶粒度在10～30 nm之间.主要研究了纳米玻璃陶瓷的吸收和发光性质,它们在可见光及近红外区域具有相似的吸收和发光特性.在这3种纳米玻璃陶瓷中,Co2 分别占据ZnAl2O4,MgAl2O4及β-锂辉石纳米晶的四面体晶格位置,四面体配位Co2 的存在是产生这些吸收和发光峰的主要原因.     

Preparation of 1,4-bis(4-methylstyryl)benzene nanocrystals by a wet process and evaluation of their optical properties

Single-crystal 1,4-bis(4-methylstyryl)benzene is a promising material for optoelectronic device applications. We demonstrate the preparation of 1,4-bis(4-methylstyryl)benzene nanocrystals by a wet process using a bottom-up reprecipitation technique. Scanning electron microscopy revealed the morphology of the nanocrystals to be sphere-like with an average particle size of about 60 nm. An aqueous dispersion of the nanocrystals was monodisperse and stable with a ζ-potential of -41 mV. The peak wavelengths of the absorption and emission spectra of the nanocrystal dispersion were blue and red shifted, respectively, compared with those of tetrahydrofuran solution. Powder X-ray diffraction analysis confirmed the crystallinity of the nanocrystals. The presented 1,4-bis(4-methylstyryl)benzene nanocrystals are expected to be a candidate for a new class of optoelectronic material.     

Co:CdS半导体纳米晶的合成、晶体结构及光学性质

利用水相合成技术,以巯基乙酸(MAA)为稳定剂,合成了Co:CdS半导体纳米晶.XRD结果表明,得到的掺杂纳米晶为闪锌矿结构,平均粒径约为3.9 nm;FT-IR结果表明,MAA成功包覆在Co:GdS纳米晶的表面;UV-vis吸收谱表明,Co离子成功掺入CdS品格中;PL结果表明,掺杂离子浓度过大会导致CdS发光淬灭;...     

Annealing temperature and environment effects on ZnO nanocrystals embedded in SiO2: a photoluminescence and TEM study

We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO₂ matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO₂ thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO₂ matrix.     

Preparation and optical properties of dispersible ZnSe nanocrystals synthesized by high energy ball milling

ZnSe nanocrystals have been successfully synthesized by high energy ball milling method. X-ray diffraction patterns show a single zinc blende structure formed in the milling process. HRTEM images confirm that the formation of the ZnSe nanocrystals synthesized by high energy ball milling have a wide crystals distribution (3–20 nm). Using the aqueous solutions of Na₃PO₄, (NaPO₃)₆ and Na₄P₂O₇ to disperse the 40 h-milled samples, we have observed the gradual blue-shift of the absorption edge along with the different centrifuging speed. In PL spectras, two main bands peaked at about 1.95 and 2.35 eV are observed, the former band is related to the V_Zn defects emission; and the latter is related to the V_Se defects emission. The V_Se defects emission does not depend on the dispersants, but the V_Zn defects emission changes in different dispersants.     

Er3+ Ions‐Doped Germano‐Gallate Oxyfluoride Glass‐Ceramics Containing BaF2 Nanocrystals

Er³⁺ ions‐doped germano‐gallate oxyfluoride glass‐ceramic containing BaF₂ nanocrystals was prepared through conventional melt quenching and subsequent thermal treatment method. X‐ray diffraction patterns and transmission electron microscope images confirmed the formation of BaF₂ nanocrystals in glass‐ceramics. Preferential incorporation of Er³⁺ ions into the BaF₂ nanocrystals were confirmed by the absorption spectra and emission spectra, and enhanced upconversion emission and infrared emission were observed. Relatively high transmittance in the mid‐infrared region indicated great potential of this germano‐gallate oxyfluoride glass‐ceramics as host materials for the efficient mid‐infrared emission from rare‐earth ions.     

On the power-dependent spectral shift of photoluminescence from ensembles of silicon nanocrystals

ABSTRACT: Nanocrystals are widely studied for their tunable optical properties, most importantly increased luminescence efficiency and emission energy. Quantum confinement effects are found for many different types of nanocrystals and these introduce a relation between the emission wavelength and size of nanocrystals. When ensembles of nanocrystals with a distribution of sizes are studied, this can have profound effects on their luminescence spectra. Here we show how photoluminescence spectra of ensembles of silicon nanocrystals can shift under different excitation conditions, resulting from differences in absorption cross section of the individual nanocrystals sizes. This effect, together with the fact that after a pulsed excitation a silicon nanocrystal can only emit a single photon, determines how the distribution of excited nanocrystals changes and leads to the spectral shift for different excitation powers. Next to this effect, also the influence of different radiative rates in such ensembles are addressed. These notions are important for interpretation of photoluminescence data for silicon nanocrystals, but can be extended to any nanoparticle system comprising size-distributed ensembles.     

Enhanced near-infrared to green upconversion from Er3+-doped oxyfluoride glass and glass ceramics containing BaGdF5 nanocrystals

In this work, effect of glass composition as well as ceramization on visible and near-infrared (NIR) luminescence properties along with their decay dynamics of Er³⁺ ions has been compared considering two different oxyfluoride glasses yielding BaF₂ and BaGdF₅ nanocrystals. Both the glass systems have exhibited an intense normal and upconversion green emission under ultraviolet (378 nm) and NIR (978 nm) excitations, respectively. A remarkable enhancement of these emission intensities is observed for gadolinium-(Gd) containing glasses. Interestingly, NIR fluorescence intensity from Er³⁺ ions at 1540 nm has showed marginal decrease in gadolinium-containing glass which is attributed to occurrence of strong excited-state absorption (ESA) due to higher fluorine content ensuing an augmentation of upconversion green emission with a concomitant decrease in NIR emission. The quadratic dependence of upconversion green emission intensity on its pump power for all the samples revealed biphotonic absorption process from ground-state ⁴I_15/2 to the excited-state ⁴I_11/2 followed by ESA of second photon to the ⁴F_7/2 level. The intense green upconversion emission as well as enhanced NIR fluorescence lifetimes indicate the suitability of these glass/glass ceramics for upconversion lasers and amplification in the third telecom window.     

Enhanced up-conversion luminescence of Er:LaOF oxyfluoride borosilicate glass ceramics

Er³⁺-doped transparent oxyfluoride borosilicate glass ceramics containing LaOF nanocrystals have been obtained by the high temperature melt-quenching and subsequent heat treatment method. The formation of LaOF nanocrystals in the glass matrix was confirmed by XRD and TEM results. In comparison with the precursor glass, Er³⁺-doped transparent oxyfluoride glass ceramics containing LaOF nanocrystals exhibited efficient up-conversion luminescence. Especially, the green emission intensity was greatly enhanced about nearly 200 times and its up-conversion mechanism can be ascribed to a two-photon absorption process.     

ZnAl2O4：Cu,Mn纳米晶的光学性能研究

采用溶胶凝胶法制备了铜锰共掺的ZnAl2O4纳米晶,使用X射线衍射和光致发光对晶体的结构和光学性能进行了研究。结果表明样品具有单一的尖晶石结构,在309 nm波长光的激发下,具有438 nm、511 nm、530 nm和617nm的光发射。随退火温度的升高,红光发射强度变强,蓝光发射随Cu2＋掺杂浓的增加而变强,CIE坐标显示纳米晶的发光在白光区域。