Yin-Hong Wang

Luminescence detection of phase transitions, local environment and nanoparticle inclusions

Luminescence data offer delicate probes of changes in structure and local environment in insulating materials. Therefore they have long been employed in studies of imperfections and characterisation of lattice distortions. Luminescence techniques are inherently very sensitive so respond to small concentrations of intrinsic defects and impurities, and intentionally added probe ions, such as rare earth or chromium ions, are particularly effective at displaying responsive changes linked to modified structural environments. Parameters of interest are variations in luminescence efficiency, the details of the emission spectra, polarisation, temperature dependence and changes in excited state lifetimes. These are suitable properties to monitor variations in both short and long range lattice structure, composition, pressure and temperature. For modern photonic materials such probes are powerful tools to follow changes introduced by processing to make waveguides, surface layers and new materials. The use of different excitation conditions for the luminescence can resolve differences between near surface and bulk features. A less common approach is to use luminescence as a route to detect phase transitions. This is particularly valuable for rapid survey studies of new materials which are of relevance to modern optics. One of the more surprising results is the observation that phase changes of very small inclusions, such as phase precipitates or impurity nanoparticles, can totally dominate the luminescence response of the bulk material. Specific examples include the frequent observation of trapped nanoparticles of water, N2, O2 and CO2. Further, the excitation techniques, and ion implantation or surface stresses can all induce surface relaxations which, in materials such as SrTiO3 or ZnO, result in phase changes propagating throughout the entire crystal. This review rapidly recalls the methods used in the older studies of imperfections and then uses a range of examples to show how luminescence studies can be effective in detecting and confirming the presence of phase transitions. Interestingly the examples include not only transparent insulating materials but also fullerenes and superconductors.

Zircon U–Pb and molybdenite Re–Os geochronology, Hf isotope analyses, and whole-rock geochemistry of the Donggebi Mo deposit, eastern Tianshan, Northwest China, and their geological significance

The geodynamic setting of Mesozoic magmatic rocks and associated mineralization in eastern Tianshan, Northwest China, are attracting increasing attention. The newly discovered giant Donggebi molybdenum deposit (0.508 Mt at 0.115% Mo) is located in the central part of eastern Tianshan, Xinjiang. The molybdenum mineralization was genetically associated with the Donggebi stock, comprised of porphyritic granite and granite porphyry. Secondary ion mass spectrometry (SIMS) zircon U–Pb dating constrains that the porphyritic granite and granite porphyry emplacement occurred at 233.8 ± 2.5 Ma and 231.7 ± 2.6 Ma, respectively. The Re–Os model ages of six molybdenite samples range from 235.2 to 237.0 Ma, with a weighted mean age of 236.1 ± 1.4 Ma, which is roughly consistent within errors with the zircon U–Pb ages, suggesting a Middle Triassic magmatic–mineralization event at Donggebi. Geochemically, the Donggebi granitoids are characterized by high SiO2 and K2O contents, with low MgO contents, belonging to high-K calc-alkaline granites. These rocks show pronounced enrichment in K, Rb, U, and Pb, and depletion in Sr, Ba, P, and Ti, with negative Eu anomalies (Eu/Eu* = 0.20–0.38). In situ Hf isotopic analyses of zircon from the porphyritic granite and granite porphyry yielded εHf(t) values ranging from +6.6 to +10.5, and from +5.5 to +10.1, respectively. The geochemical and isotopic data imply that the primary magmas of the Donggebi granitoids could have originated by partial melting of a juvenile lower crust that involved some mantle components. Combined with the regional geological history, geochemistry of the Donggebi granitoids, and new isotopic age data, we thus propose that the Donggebi molybdenum deposit was formed in the Middle Triassic, and occurred in an intracontinental extension setting in eastern Tianshan.

Petrogenesis of Late Carboniferous granitoids in the Chihu area of Eastern Tianshan, Northwest China, and tectonic implications: geochronological, geochemical, and zircon Hf–O isotopic constraints

ABSTRACT This contribution presents new SIMS zircon U–Pb geochronology, major and trace element geochemistry, and zircon Hf–O isotope systematic on an example of Late Carboniferous granodiorite and porphyritic granodiorite intrusions from the Chihu area of Eastern Tianshan, Xinjiang. SIMS zircon U–Pb dating indicates that the Chihu granodiorite and porphyritic granodiorite formed at 320.2 ± 2.4 Ma and 314.5 ± 2.5 Ma, respectively. These rocks are metaluminous to weakly peraluminous with an A/CNK value of 0.92–1.58, as well as low 10000 Ga/Al, Zr + Nb + Y + Ce, and Fe2O3T/MgO values, which suggest an I-type normal island arc magmatic suite. The porphyritic granodiorite has a slightly higher Sr/Y ratio (28–37) and lower Y (6.9–11.7 ppm) and Yb (0.98–1.49 ppm) contents, suggesting mild adakite affinities. In situ Hf–O isotopic analyses using LA-ICP-MS-MC and SIMS indicate that the εHf(t) and δ18O values of granodiorite zircons vary from +11.5 to +14.9 and 4.80 to 5.85 ‰, respectively, similar to values for porphyritic granodiorite zircons, which vary from +11.9 to +17.2 and 3.78 to 4.71 ‰, respectively. The geochemical and isotopic data imply that the Chihu granodiorite and porphyritic granodiorite share a common origin, most likely derived from partial melts of the subduction-modified mantle. Based on the regional geological history, geochemistry of the Chihu intrusions, and new isotopic studies, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Palaeo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc.

Correlations between low temperature thermoluminescence and oxygen vacancies in ZnO crystals

Low temperature thermoluminescence spectra of zinc oxide single crystals are presented in this paper. The signals can be interpreted in terms of annealing and inter-conversion of oxygen vacancy sites. Minor differences between signals from different suppliers suggest such vacancies are perturbed by association with complexes and impurities. Significant changes of bulk signals result from high dose surface ion implantation. This is an important demonstration of extremely long range effects resulting from ion implantation into the surface layer. Such extensive changes have rarely been considered, or experimentally sought. It is therefore fortunate that for ZnO the thermoluminescence signals offer a sensitive probe to monitor this phenomenon.

Structural changes and relaxations monitored by luminescence

Luminescence data have often been used to study imperfections and to characterize lattice distortions because the signals are sensitive to changes of structure and composition. Previous studies have included intentionally added probe ions such as rare earth ions to sense distortions in local crystal fields caused by modified structural environments. An under-exploited extension of this approach was to use luminescence to monitor crystalline phase changes. A current overview of this new and powerful technique shows that continuous scanning of the sample temperatures immediately offered at least three types of signatures for phase transitions. Because of high sensitivity, luminescence signals were equally responsive to structural changes from inclusions and nanoparticles. These coupled to the host material via long-range interactions and modified the host signals. Two frequently observed examples that are normally overlooked are from nanoparticle inclusions of water and CO2. Examples also indicated that phase transitions were detected in more diverse materials such as superconductors and fullerenes. Finally, luminescence studies have shown that in some crystalline examples, high dose ion implantation of surface layers could induce relaxations and/or structural changes of the entire underlying bulk material. This was an unexpected result and therefore such a possibility has not previously been explored. However, the implications for ion implication are significant and could be far more general than the examples mentioned here.

Substrate lattice relaxations, spectral distortions, and nanoparticle inclusions of ion implanted zinc oxide

Low temperature radioluminescence and thermoluminescence spectra of ZnO track numerous changes produced by copper ion implantation into the surface layer. A significant, but unexpected, feature is that the bulk crystal becomes modified by the stress generated in the surface layer. This is reflected by the energy of intrinsic band gap emission. There are also differences in the spectra and peak temperatures of the thermoluminescence components, consistent with such a structural relaxation. The copper implant layer is both absorbing and reflective, so this introduces major distortions on the radioluminescence component from the bulk region, since the bulk luminescence signals are transmitted through, or reflected from, the implant layer. The temperature dependence of the spectra includes anomalies that are typical of changes driven by phase transitions of nanoparticle inclusions. Overall, the features of bulk relaxation, spectral distortion, and detection of nanoparticle inclusions are rarely considered for...

Indications of bulk property changes from surface ion implantation

In the majority of cases, the effects of ion implantation are confined close to the implant zone but, potentially, the resultant distortions and chemical modifications could catalyse relaxations extending into the bulk substrate. Such possibilities are rarely considered but the present data suggest that high dose ion implantation of ZnO has induced bulk changes. Surface implants with Cu and Tb strongly modified the low temperature bulk thermoluminescence properties generated by X-ray irradiation. Suggestions are proposed for the possible mechanisms for bulk relaxations and structural characteristics, which may indicate where such instability may occur in other lattice structures.

Luminescence detection of nanoparticle inclusions from their phase transitions

Nanoparticle inclusions in insulators from contaminants dramatically alter host luminescence properties of intensity and spectra. Their presence is readily revealed if, during heating or cooling, the nanoparticles undergo phase transitions, as their structural changes modify the host signals. Examples cited include both bulk contaminants retained from growth, and impurities and changes from surface reactions and in-diffusion. Phase changes from impurities such as water ice, oxygen, nitrogen, argon, or carbon dioxide can alter the host emission intensity by factors of ten to a hundred times, and also distort the spectra. Such nanoparticle inclusions are detectable in many insulators. Unfortunately, not only does this imply that published data of luminescence performance efficiency may often have been compromised, but the examples of pressure transitions controlling long range interactions within the host lattice mean they distort not only luminescence signals, but also many electrical and other responses. ...

Photoluminescence identification of surface contaminants on zinc oxide from their phase transitions

Abstract The spectra of photoluminescence (PL) from a zinc oxide (ZnO) crystal included an unusual feature of an ultraviolet (UV) emission at a higher energy than the ZnO interband transitions. The energy of this UV emission varied with temperature and included two discontinuous energy steps in the temperature range from 78 to 700 K. The temperature values of the steps match phase transition temperatures of ethanol. Ethanol was used during sample cleaning and can be trapped in the form of nanoparticles inclusions. Both the intrinsic and defect site, PL signals have different temperature dependencies from those of bulk crystals, as seen during radioluminescence. The origins of the changes are discussed.