Y. G. Zhang

Bright white upconversion luminescence in rare-earth-ion-doped Y2O3 nanocrystals

Room temperature bright white upconversion (UC) luminescence in Yb3+–Tm3+–Er3+ ions doped Y2O3 nanocrystals was obtained under single-wavelength diode laser excitation of 976nm. The white light consists of the blue, green, and red UC radiations which correspond to the transitions G41→H63 of Tm3+, H11∕22∕S3∕24→I15∕24, and F9∕24→I15∕24 of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses. The calculated color coordinates display that white light can be achieved in a wide range of pumping powers, which promises their potential applications in the field of displays, lasers, photonics, and biomedicine.

Two-color upconversion in rare-earth-ion-doped ZrO2 nanocrystals

To develop fluorescent labels for multicolor imaging, rare-earth-ion-doped ZrO2 nanocrystals were prepared by a complex precursor method. Laser excitation of 976nm induced single fluorescent bands of green and red upconversion (UC) in ZrO2:Er3+ and ZrO2:Er3++Yb3+ nanocrystals, respectively. A suppression ratio (SR) parameter was introduced, defined as the UC intensity ratio of the main band to all the other detected impurity bands, and SR values in the order of 10–100 were experimentally obtained, demonstrating the excellent monochromaticity of the UC labels. Thus, the two-color UC labels obtained are potentially ideal to be used for biological multicolor imaging.

Simultaneous detection of multiple-gas species by correlation spectroscopy using a multimode diode laser

Simultaneous detection of multiple-gas species has for the first time (to our knowledge) been demonstrated by using a multimode diode-laser-based correlation spectroscopy (MDL-COSPEC) scheme. Concentration measurements of a mixture of CO(2) and CO gas were performed by probing overlapping line spectra around 1.57microm using an MDL. Species identification and corresponding quantitive analysis were implemented by correlating the recorded absorption signals of the sample gas mixtures with those of the reference gases of particular interest, attaining accuracies of 2% and 1%, respectively. MDL-COSPEC is a generic technique with potential application for simultaneous detection of multiple gases having resolvable narrow lines.

Concentration evaluation method using broadband absorption spectroscopy for sulfur dioxide monitoring

We report on an approach for sulfur dioxide monitoring using broadband absorption spectroscopy in the ultraviolet spectral range. The method was applied in real-time measurements and has the advantage of straightforward data evaluation, limited susceptibility for interference from other gases, and low degree of complexity compared with other real-time optical detection techniques having the same precision. Concentration measurement is demonstrated at atmospheric pressure, which is of interest for pollution emission monitoring, yielding a detection limit of about 1ppm with 3s integration time. Comparison is made with low pressure measurements for validation of the accuracy of the method.

Nitrogen dioxide monitoring using a blue LED

We report on a monitoring technique for nitrogen dioxide based on broadband absorption spectroscopy using a blue light-emitting diode (LED) operating around 465 nm. The technique is suited for real-time measurements of nitrogen dioxide due to the use of a straightforward data evaluation method, limited interference from other gases, and a low degree of complexity compared with other real-time optical detection techniques having the same precision. Additionally, the use of a LED can reduce the cost of nitrogen dioxide monitoring. Real-time measurements of nitrogen dioxide concentration were demonstrated at atmospheric pressure, which is of great interest for industrial nitrogen dioxide emission monitoring; a detection limit of about 3 ppm using a 50-cm-long gas cell with 2 s integration time was achieved.

Broadband spectroscopic sensor for real-time monitoring of industrial SO(2) emissions.

A spectroscopic system for continuous real-time monitoring of SO(2) concentrations in industrial emissions was developed. The sensor is well suited for field applications due to simple and compact instrumental design, and robust data evaluation based on ultraviolet broadband absorption without the use of any calibration cell. The sensor has a detection limit of 1 ppm, and was employed both for gas-flow simulations with and without suspended particles, and for in situ measurement of SO(2) concentrations in the flue gas emitted from an industrial coal-fired boiler. The price/performance ratio of the instrument is expected to be superior to other comparable real-time monitoring systems.

Diffuse reflectivity measurement using cubic cavity.

A method for measuring diffuse reflectivity using cubic cavity based on the variable port fraction method was developed by measuring oxygen P11 line at 762 nm using tunable diode laser absorption spectroscopy. An experimental method to determine the additional path length l0 was presented. We measured the diffuse reflectivity of a cubic cavity with scattering coatings of different thickness. The error of diffuse reflectivity was reduced from 0.004 to 0.0003 when the diffuse reflectivity increased from 0.867(4) to 0.9887(3). A simulation result manifests that the error of diffuse reflectivity has the potential to be further reduced at higher diffuse reflectivity.