Highly efficient and tunable fluorescence of a nanofluorophore in silica/metal dual shells with plasmonic resonance

A dual-shell structure consisting of a silica buffer shell and a metallic outer shell is studied and designed for highly efficient and tunable fluorescence. The enhanced Purcell effect due to the plasmonic resonance and the dependence of the resonance on the structural parameters are analyzed and discussed through a classical electromagnetic approach. With the present dual-shell structure a fivefold enhancement of the fluorescence efficiency can be achieved for a nanofluorophore comprised of multiple tetramethylrhodamine isothiocyanate dye molecules, as compared to the nanofluorophore within a single silica shell. Furthermore, the peak wavelength of the fluorescence spectrum can be tuned easily (due to the variation of the surface plasmon resonance) by over 50 nm when the refractive index of the ambient material varies from 1.3 to 1.6. © 2008 American Institute of Physics.published_or_final_versio

Comprehensive analysis and optimal design of top-emitting organic light-emitting devices

We present an accurate analysis of light emission in top-emitting organic light-emitting devices (TOLEDs) by explicitly considering the Purcell effect. TOLEDs are optimized separately for maximum zero-degree luminance, maximum electroluminescence (EL) efficiency, and wide viewing angle with high EL efficiency. For fluorescent material with an internal quantum efficiency ( int 0) of 0.25, the maximum zero-degree luminance and EL efficiency can be achieved by locating the emitters around the first antinode of the microcavity while for phosphorescent material with int 0 =1.0, the maximum zero-degree luminance and EL efficiency are around the second antinode. Through relaxing the efficiency by 10%-20%, the angular intensity distribution can be even better than the Lambertian distribution; meanwhile, the color shows only a small variation over an angle range of 150°. Our results, which are in good agreement with experiments, show that the Purcell effect on TOLED performances is significant and should be carefully examined in studying TOLEDs. © 2007 American Institute of Physics.published_or_final_versio

Highly efficient fluorescence of a fluorescing nanoparticle with a silver shell

Spontaneous emission (SE) rate and the fluorescence efficiency of a bare fluorescing nanoparticle and the nanoparticle with a silver nanoshell are analyzed rigorously by using a classical electromagnetic approach with the consideration of the nonlocal effect of the silver nanoshell. The dependences of the SE rate and the fluorescence efficiency on the core-shell structure are carefully studied and the physical interpretations of the results are addressed. The results show that the SE rate of a bare nanoparticle is much slower than that in the infinite medium by almost an order of magnitude and consequently the fluorescence efficiency is usually low. However, by encapsulating the nanoparticle with a silver shell, highly efficient fluorescence can be achieved as a result of a large Purcell enhancement and high out-coupling efficiency for a well-designed core-shell structure. We also show that a higher SE rate may not offer a larger fluorescence efficiency since the fluorescence efficiency not only depends on the internal quantum yield but also the out-coupling efficiency. © 2007 Optical Society of America.published_or_final_versio

The Purcell effect of silver nanoshell on the fluorescence of nanoparticles

Proceedings of the Asia Optical Fiber Communication and Optoelectronics Conference, 2007, p. 81-83The Purcell effect on the spontaneously emission rate and fluorescence efficiency of nanoparticles with and without a silver nanoshell will be investigated which are important for nanoparticle applications in biomedical diagnostics, information storage and optoelectronics.published_or_final_versio

Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity

A comprehensive analysis is given on the modifications of the exciton lifetime and internal quantum efficiency (int) for organic light-emitting devices (OLEDs). A linear relation is derived between the exciton lifetime and int, which is difficult to measure directly. The internal quantum efficiency can thus be estimated easily through the measurement of the exciton lifetime. The exciton lifetimes for OLEDs with weak or strong microcavity are studied experimentally and theoretically. The modification of the exciton lifetime is well explained through the microcavity effect and surface plasmon resonance. An excellent agreement between the experimental and theoretical results is achieved. © 2007 American Institute of Physics.published_or_final_versio

Cassiterite oxygen isotopes in magmatic-hydrothermal systems: in situ microanalysis, fractionation factor, and applications

Tin and tungsten are important metals for the industrializing society. Deciphering the origin and evolution of hydrothermal fluids responsible for their formation is critical to underpin genetic models of ore formation. Traditional approaches obtain isotopic information mainly from bulk analysis of both ore and gangue minerals, or less frequently from in situ analysis of gangue minerals, which either bear inherited complexities and uncertainties or are indirect constraints. Hence, directly obtaining isotopic information from ore minerals such as cassiterite by in situ techniques is warranted. However, this has been hampered by challenges from both analytical and applicational aspects. In this study, we first demonstrate a lack of crystallographic orientation effects during cassiterite ion microprobe oxygen isotope analysis. Along with our newly developed matrix-matched reference material, the Yongde-Cst, which has a recommended δ18O value of 1.36 ± 0.16‰ (VSMOW) as defined by gas source isotope ratio mass spectrometry, in situ oxygen isotope analysis of cassiterite now is possible. We further refine the oxygen isotope fractionation (1000 ln α) for quartz-cassiterite by first-principles calculations, which is given by the equation of 1.259 × 106/T2 + 8.15 × 103/T − 4.72 (T is temperature in Kelvin). The 1000 ln α for quartz-cassiterite has a sensitive response to temperature, and makes cassiterite-quartz an excellent mineral pair in oxygen isotope thermometry, as described by the equation of T (℃) = 2427 × (δ18Oqtz − δ18Ocst)−0.4326 − 492.4. Using the well-established 1000 ln α of quartz-water, 1000 ln α of cassiterite-water is derived as 2.941 × 106/T2 − 11.45 × 103/T + 4.72 (T in Kelvin), which shows a weak response to temperature. This makes cassiterite an ideal mineral from which to derive δ18O of fluids as robust temperature estimates are no longer a prerequisite. We have applied oxygen isotope analysis to cassiterite samples from six Sn(-W) deposits in China. The results show considerable variability in δ18O values both within a single deposit and among studied deposits. Combining the δ18O of cassiterite samples and the equilibrium oxygen isotope fractionation, we find that the δ18O values of ore-forming fluids show a strong magmatic affinity with variable but mostly no to low degree involvements (~0-10%) of meteoric water, hence our results invite a reassessment on the extent and role of meteoric water in Sn-W mineralization. This study demonstrates that in situ oxygen isotope analysis of cassiterite is a promising tool to refine sources of ore-forming fluids, and to decode hydrothermal dynamics controlling tin and tungsten mineralization

Modifications of the exciton lifetime and internal quantum efficiency for organic light-emitting devices with a weak/strong microcavity

Author name used in this publication: P. K. A. Wai2007-2008 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe

MiR-637 maintains the balance between adipocytes and osteoblasts by directly targeting Osterix

Bone development is dynamically regulated by homeostasis, in which a balance between adipocytes and osteoblasts is maintained. Disruption of this differentiation balance leads to various bone-related metabolic diseases, including osteoporosis. In the present study, a primate-specific microRNA (miR-637) was found to be involved in the differentiation of human mesenchymal stem cells (hMSCs). Our preliminary data indicated that miR-637 suppressed the growth of hMSCs and induced S-phase arrest. Expression of miR-637 was increased during adipocyte differentiation (AD), whereas it was decreased during osteoblast differentiation (OS), which suggests miR-637 could act as a mediator of adipoosteogenic differentiation. Osterix (Osx), a significant transcription factor of osteoblasts, was shown to be a direct target of miR-637, which significantly enhanced AD and suppressed OS in hMSCs through direct suppression of Osx expression. Furthermore, miR-637 also significantly enhanced de novo adipogenesis in nude mice. In conclusion, our data indicated that the expression of miR-637 was indispensable for maintaining the balance of adipocytes and osteoblasts. Disruption of miR-637 expression patterns leads to irreversible damage to the balance of differentiation in bone marrow. © 2011 Zhang et al.published_or_final_versio