Chu Guoqiang

Effect of emitter position on emission intensity in an organic planar microcavity

We have fabricated a λ/2-length planar microcavity between two silver mirrors that had the same thickness and consisted of a sandwich structure LiF1/Alq3/LiF2. By altering the relative thickness of the two LiF layers, the adjustment of the position of thin layer Alq3 in the microcavity was achieved and the apparent photoluminescence (PL) intensity change was observed. The maximal emission intensity device, corresponding to the luminescence layer located at antinode, is four times that of the minimal one whose luminescence layer is near a silver mirror that is close to a node. This indicates that the coupling between vacuum electric field and dipole strongly affects the emission intensity in the forward direction of the microcavity plane. Comparing the PL intensity between the microcavity and the non-cavity devices with the same sandwich structure LiF1/Alq3/LiF2 in free space, at the resonance wavelength a maximal enhancement factor of nine is obtained.

Vegetation history and climate change recorded by stomata evidence during the late glacial in the Great Khingan Mountain Region, Northeastern China

The research on the evolution of larch forest is significant to understand the vegetation and climate change in mid-high latitude region of the Northern Hemisphere. However, the pollen records to reconstruct the larch forest are problematic due to low pollen representation caused by severely poor pollen productivity and dispersal. New proxy of microfossils is needed to solve this problem. Using coniferous stomata as a proxy to reconstruct the evolution of conifers has some advantages, such as well preserved, locally deposited, continuously remained in lake sediments and can be accurately identified to the genus level. Therefore, a high-resolution stomata record covering 20.3–10.8 cal ka BP from Lake Moon was presented, in order to reconstruct larch forest history from the Last Glacial Maximum to early Holocene in the Great Khingan Mountain Region, Northeast China. Reference conifer stomata from fresh leaves of the local coniferous species and lake surface samples were prepared for the identification of the fossil stomata. Larix , Sabina and Picea stomata were identified from the sedimentary sequence of Lake Moon, and the results of stomata influx from this study and pollen influx from the previous study indicate that the vegetation evolution has gone through distinct stages. Before 15.0 cal ka BP, no Larix existed in the vicinity of study site. The first arrival of larch is inferred by the continuous presence of stomata at 15.0 cal ka BP, which manifests that the vegetation turned into forest steppe. The coverage of forest increases slightly from 15.0 to 12.8 cal ka BP with an interruption between 14.3 and 14.0 cal ka BP. During 12.8–11.8 cal ka BP, the vegetation were characterized by the expansion of conifers mainly Larix and the shrinkage of broadleaves and herbs. From 11.8 to 10.8 cal ka BP, the vegetation type remained as forest steppe with the shrinkage of conifers dominated by Larix , in conjunction with the expansion of broadleaves and herbs with high vegetation coverage. The establishment of larch forest inferred by the continuous presence of stomata marks the onset of the late glacial in the Great Khingan Mountain Region at 15.0 cal ka BP. The application of stomata analysis provides detailed scenes of coniferous evolution surrounding the Lake Moon. It is suggested that the analysis of fossil stomata is a valuable tool to demonstrate unambiguous evidence for the local presence of the conifers in study region, even better than pollen records when the component of larch is low in vegetation. The evolution of the forest communities in the late glacial period in the Great Khingan Mountain Region is comparable with the vegetation evolution of other regions at different latitudes in East Asian monsoon region, which indicates that the climate change at millennial/centennial scale in late glacial is roughly synchronous in East Asian monsoon region. The series of climatic periods in this study revealed by the stomata and pollen records is also similar to that of Europe, like Meiendorf interstadial, Oldest Dryas cold event, Bolling-Allerod warm phases, Younger Dryas cold event, warm and humid early Holocene. The temperature change is probably the main factor to impact the vegetation change. The study shows that the vegetation succession in the study area is responsive to the temperature change of the Northern Hemisphere controlled by the global ice volume, and reveals the synchronization of the late glacial climate change in the mid latitude region of East Asia and the North Atlantic region.

Three-colour single-mode electroluminescence from Alq3 tuned by microcavities

Organic metal microcavities were fabricated by using full-reflectivity aluminium film and semi-transparent silver film as cavity mirrors. Unlike conventional organic microcavities, such as the typical structure of glass/DBR/ITO/organic layers/metal mirror, a microcavity with a shorter cavity length was obtained by using two metal mirrors, where DBR is the distributed Bragg reflector consisting of alternate quarter-wave layers of high and low refractive index materials. It is realized that red, green and blue single-mode electroluminescence (EL) from the microcavities with the structure, glass/Ag/TPD/Alq3/Al, are electrically-driven when the thickness of the Alq3 layer changes. Compared to a non-cavity reference sample whose EL spectrum peak is located at 520 nm with a full width at half maximum (FWHM) of 93 nm, the microcavity devices show apparent cavity effects. The EL spectra of red, green and blue microcavities are peaked at 604 nm, 540 nm and 491 nm, with FWHM of 43 nm, 38 nm and 47 nm, respectively.

火山灰全岩与原位分析差异：以四海龙湾记录的1 600年前金龙顶子火山喷发为例

火山灰地层学主要依靠火山玻璃的成分进行源区的识别，然而，当火山玻璃成分不均一时就会对源区识别造成影响.四海龙湾玛珥湖位于东北新生代龙岗火山区内，其湖泊沉积物可以记录周边的火山喷发，电子探针等方法得到的火山玻璃成分可以揭示其喷发来源.同时，玛珥湖的纹层年龄可以限定其喷发年龄.在四海龙湾沉积物(钻孔2008) 的78~79 cm岩芯处出现一层火山灰层，其纹层年龄为AD 308 a，电子探针结果显示火山玻璃具有不均一的主量元素组成，为玄武质粗安岩到碱玄质响岩.FeO、TiO2及Al2O3等与MgO协变图解更清楚地显示了此次火山喷发的火山玻璃成分的不均一性.火山玻璃与火山灰全岩对比分析显示，全岩分析在火山灰地层学应用中容易造成对比偏差.

Microanalytical study of varves in the recent sediments of Lake Bele

The inner structure of varves in the recent sediments of Lake Bele, Khakassia, is studied via X-ray fluorescence microanalysis at the Siberian and Shanghai Centers of Synchrotron Radiation. Similar experimental conditions apply in both cases: excitation energy, 20–22 keV; size of exciting radiation spot, 80–100 μm; scanning step, 100 μm. The dates determined for marking layers coincide. The experimental results shed new light on the geochemistry of sedimentation processes and help estimate the current sedimentation rate.

Tracing the Provenance of the Huguangyan Maar Lake Sediments in Coastal Regions of South China

The Huguangyan Maar Lake(HML)(21°9’N,110°17’E),situated on the Leizhou Peninsula in the southernmost of mainland China,is the deepest recent crater lake among the identified volcanic structures in the Leiqiong Volcanic Field.The bi-lobate lake,with a diameter of~1.7 km and