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Dye-doped hemispherical resonators are self-assembled on a distributed Bragg reflector based on hydrophobic effect. The size of hemispheres can be well-controlled with diameters ranging from 5 to 150 μm. Upon optical pumping, whispering gallery mode laser emission with transverse magnetic polarization is observed from the hemispheres. Application of the microlasers as refractive index gas sensors has been demonstrated by detecting the spectrum shift of the lasing mode, and the sensitivity higher than 130 nm/RIU is achieved. Our approach provides an effective technique to obtain high quality microlasers and opens an opportunity to employ the cost effective microlasers as high sensitive sensors.

Photoluminescence (PL) properties of tin oxide (SnO 2 ) nanowires are studied in detail using high spectral resolution spectroscopy in a temperature range of 10-300 K. The nanowires have an average diameter of 86 nm. The high quality of the nanowires enables the observation of rich fine structures in the ultraviolet PL spectra at low temperatures. By carefully analyzing the temperature and excitation power dependent spectra, the following emissions are identified: recombination of donor-acceptor pairs, excitons bound to neutral and ionized donor impurities and optical transitions from free electrons to neutral acceptor impurities. Moreover, it is believed that the emission from recombination of free excitons is observed, which is unusual for SnO 2 , a dipole forbidden direct band gap semiconductor.

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Intense near-infrared (NIR) emission around 1534 nm has been obtained from ZnO-SiO2:Er3+ composites upon broadband ultraviolet light excitation. Remarkably, enhancement of the NIR emission as much as 20 times was achieved by optimal codoping with Li+ ions. To elucidate the relevant mechanisms, comprehensive spectroscopic measurements have been performed on ZnO-SiO2 composites with and without Er3+ ions doping. Photoluminescence spectroscopy and fluorescence decay dynamics clearly verify the efficient energy transfer from ZnO quantum dots (QDs) to Er3+ ions. Our results have not only demonstrated an efficient approach of color down-conversion but also indicated that ZnO-SiO2:Er3+ composites could be a promising material for optical amplifier using broadband UV pumping.