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We discuss the synthesis of cuboid-monoclinic tungsten oxide (C-m-WO3) particles and hexagonal-plate-like-hexagonal tungsten oxide (H-h-WO3) particles by acidification and hydrothermal treatment with (NH4)10W12O41·5H2O as a starting material. From the WO3 particles, thin- and thick-film gas sensors were fabricated for NO2 sensing applications and the effect of the morphology and crystal structure of the WO3 particles on the NO2 sensing properties was investigated. The extremely high sensor responses of 160 to 20 ppb NO2 and 10 120 to 500 ppb NO2 were obtained for a C-m-WO3 thin-film sensor at an operating temperature of 200 °C. The crystal structure features of as-prepared particles were studied by XRD, XPS, SEM, TEM, and solid state 1H and 13C NMR measurements. The presence of residual impurities, cations, and high density of surface OH− in the H-h-WO3 particles was demonstrated, which could be one of the key reasons for the crystal structure dependence of the sensing properties in C-m-WO3 and H-h-WO3 gas sensors.

The fluorescence characteristics of different Ce3+:Er3+-codoped fluoride host glasses, such as fluorozirconate and fluoroindate glass, are reported. It is shown that Ce3+ codoping into Er3+ doped fluoride glasses resulted in a quenching of Er3+ ions from the 4I11/2 to the 4I13/2 state, and the branching ratio for the Er3+ 4I11/2→4I13/2 transition increased from 0.20 to over 0.80 by codoping 2.0 mol % Ce3+. Further, the fluorescence quantum yield at 1.55 μm was also significantly improved. A Ce3+:Er3+-codoped fluorozirconate fiber laser operating at 1.55 μm band with 980 nm excitation has been realized for the first time, which clearly indicates the effectiveness of Ce3+ codoping.

To improve 1.55 /spl mu/m band fluorescence, Ce and Yb were doped into Er doped ZBLAN glasses, the fluorescence characteristics and energy transfer dynamics of Ce:Er:Yb:ZBLAN glasses were investigated.

Optical glasses doped with a fullerene mixture of C60/C70 were made in our lab. Three peaks, corresponding to C60, C70, and a modified fullerene (possibly its oxide), respectively, were found in the chromatogram of high performance liquid chromatography (HPLC) analysis of the 0.1‐wt % fullerene doped phosphate glass. Depending on the doping procedure and impurity, weak to strong interacting between C60 and its environment was found by the nuclear magnetic resonance study. For both phosphate and fluorophosphate glasses with 0.01‐wt % fullerene mixture doping, the eigen UV absorption edge showed a significant blueshift, indicating that the bonding between the nonbridging oxygen in these glasses was subjected to a strong change due to the fullerene doping.

We present the experimental results on how to suppress self‐mode‐locking in a free‐run or Q‐switched Nd:YAG laser with intracavity fullerenes. It was demonstrated that the self‐mode‐locking was partly or completely suppressed when a certain sample containing fullerenes, such as C60 toluene solution, C60 in polystyrene host, or optical glass doped with fullerenes, was placed within the laser resonator, and that the degree of suppression was dependent upon the length and fullerenes concentration of the sample. Qualitative analysis showed that the nonlinear absorption of the intracavity fullerenes resulted in this effect.

The fluorescence characteristics of Er/sup 3+/ codoped with Ce/sup 3+/ or Yb/sup 3+/ in ZBLAN glass were studied. It was found that the 1.55 /spl mu/m band fluorescence characteristics can be effectively improved by Ce/sup 3+/-codoping, and dynamics of the transfer and back transfer among Yb/sup 3+/ and Er/sup 3+/ ions in fluoride glasses can be well described by the energy transfer model.

Four types of WO3 particles, spherical, disk, cuboid, and hexagonal, were prepared and WO3 film sensors were deposited on Au comb-type microelectrodes by dropping suspension using the various WO3 powders obtained. The sensing properties to dilute NO2 revealed that the cuboid WO3 film sensor had the best response-recovery characteristics with the 90% response and 90% recovery times of 1.3 and 0.9 min to 0.05 ppm NO2 at 200°C, respectively. On the other hand, the hexagonal WO3 film sensor showed extremely high sensor response of 41.1 even to 0.01 ppm NO2 at 200°C, but the sensor response fluctuates widely with the operating temperature ranging from 80 to 300 °C. The adsorption-desorption behaviours of NO2 on various surfaces of WO3 particles with different morphologies were investigated using temperature programmed desorption (TPD) technique, which suggesting that NO2 molecules were adsorbed easily on the WO3 surface. The desorbed amount of NO decreased in the order of hexagonal, cuboid, disk and spherical, which agreed with the respective sensor response of the four WO3 film sensors.

The fluorescence characteristics of Ce3+:Er3+ codoped fluoride glass are reported. It is observed that the decay rate of the 4I11/2 state of Er3+ increased by increasing the Ce3+ concentration. Further, the branching ratio for the transition from the 4I11/2 state to the 4I13/2 state of Er3+ increased from 0.20 to 0.95 by codoping 6.0 mol% Ce3+ into Er3+-doped ZBLAN-H fluoride glass. As a result, the 1.55 µm fluorescence quantum yield has been significantly improved.