Zhimin Peng

Concentration measurement of NO using self-absorption spectroscopy of the γband system in a pulsed corona discharge

Nitric oxide (NO) concentrations were measured using the γ band system spectrum based on the strong self-absorption effect of NO in pulsed corona discharges. The radiative transitional intensities of the NO γ band were simulated based on the theory of molecular spectroscopy. The intensities of some bands, especially γ(0,0) and γ(1,0), are weakened by the self-absorption. The correlations between the spectral self-absorption intensities and NO concentration were validated using a modified Beer-Lambert law with a combined factor K relating the branching ratio and the NO concentration, and a nonlinear index α that is applicable to the broadband system. Optical emissive spectra in pulsed corona discharges in NO and N2/He mixtures were used to evaluate the two parameters for various conditions. Good agreement between the experimental and theoretical results verifies the self-absorption behavior seen in the UV spectra of the NO γ bands.

Novel full color greenish-white-emitting Sr3Bi(PO4)3∶Eu2+ phosphor for white light-emitting diodes

Abstract. The full color greenish-white-emitting phosphors Eu2+-doped Sr3Bi(PO4)3 have been successfully synthesized by the conventional solid-state reaction, and its photoluminescence properties have been investigated for the first time. The emission spectra of Sr3Bi(PO4)3∶Eu2+ phosphors exhibit a greenish-white-emitting by combining blue, green, and red emissions, which are originated from the 5d→4f transition of the Eu2+. The excitation spectra reveal broad strong bands from 300 to 400 nm, which match well with the readily available emissions from near-ultraviolet light-emitting diode (LED) chips. The correlated color temperature, color rendering index (CRI), and Commission Internationale de I’Eclairage chromaticity coordinates of the entitled phosphors excited by 330 and 365 nm are also investigated. The experimental results indicate that the Eu2+-doped Sr3Bi(PO4)3 phosphors are a promising innovative greenish-white-emitting phosphor for white LEDs.

Wavelength modulation spectroscopy for recovering absolute absorbance

A highly sensitive, calibration-free method, wavelength modulation - direct absorption spectroscopy (WM-DAS), is proposed by extracting the characteristic frequencies of modulated laser intensity. This method combines the advantages of measuring absolute absorbance profile from calibration-free DAS with the enhanced noise rejection and high sensitivity of WMS. The preliminary validation experiment of H2O transitions shows that the WM-DAS method improves the accuracy of the absorbance profile measurement with a best-fit standard residual of 4.9 × 10-5. This new method might inspire new approaches to high-precision measurement of spectral line parameters and gas information with weak absorptions or industrial applications.

Non-uniform temperature measurement of flat flames using TDLAS

Tunable Diode Laser Absorption Spectroscopy (TDLAS) is a non-intrusive method of measurement, which has lots of advantages, such as real-time, fast response, high sensitivity, easy operation, harsh condition applicability and so on. In this paper, the 7173.781201 and 7199.37761 cm-1 line pair of water vapor were selected for the temperature measurement of the flat flame burner. In order to observe the non-uniform temperature distribution, the Fourier-Hankel transform in the inverse Abel transform was used to convert the integrated temperature, which got by TDLAS, into temperature field.

Shock Tube Experimental Studies on CH*/Visible Light/Pressure as Ignition Delay Criteria

Ignition delay time is a key parameter in evaluating the ignition processes of fuel mixtures. By using shock tube experiments, this paper compares three ignition criteria, namely, CH*, visible light, and pressure under high and low diluent conditions, respectively. Main comparison principles include signal-to-noise ratio, readability of signal curves, and model validation. Different types of CH* and visible light response curves are displayed. Experimental results indicate that CH* is the most appropriate ignition criterion under high diluent conditions. Visible light is the second most suitable choice, whereas pressure is unsuitable as the ignition criterion. Under low diluent conditions relevantly, CH*, visible light, and pressure can all be used as the ignition criteria. Moreover, visible light signals generally occur later than CH*, and the visible-light reading results are correspondingly larger, whereas an overlarge gain factor can result in smaller visible-light reading results than those of CH*. I...

Temperature and absolute oh density measurement by the relative emission spectroscopy in diffuse atmospheric-pressure RF glow discharges

Summary form only given. In recent years, the measurement of absolute densities of reactive species and radicals such as OH is of growing interest for many plasma applications. Many complex techniques, including laser-induced fluorescence (LIF), cavity ring-down spectroscopy, resonant absorption and broadband absorption, have been used to measure absolute OH density. However, the optical emission spectroscopy (OES) has the natural advantage of being non-intrusive, inexpensive, and easy to implement, in comparison with the abovementioned methods.In this contribution, we will extend the use of a selfabsorption model for atomic emission spectroscopy1, 2 to molecular emission spectroscopy, in particular OH(A-X). We propose to analyze the self-absorption effect on rotational lines in the emission spectra of OH(A-X) for the simultaneous measurement of gas temperature and OH(X) density. We apply the model on emission spectra recorded from a 10 cm homogeneous and diffuse glow discharge which is optically thick for the OH(A-X) emission. The effect of gas temperature, rotational temperatures, and spectral resolution of the spectrometer is assessed. The outcomes are compared in detail with OH densities measured by broadband absorption and gas temperatures by OES of N2(C-B) to validate the proposed method. The detection limit of the line integrated OH(X) density with this method is of the order of 2 × 1019 m-2. The accuracy of the density is sensitive to the rotational temperature of the OH(A) state and the nonequilibrium rotational population distribution. The proposed analysis of self-absorbed optical emission spectra is a simple and inexpensive method to determine OH densities, in large volume plasmas although it requires a high-resolution spectrometer.

Calibration-free self-absorption model for measuring nitric oxide concentration in a pulsed corona discharge

The effect of self-absorption on emission intensity distributions can be used for species concentration measurements. A calculation model is developed based on the Beer-Lambert law to quantify this effect. And then, a calibration-free measurement method is proposed on the basis of this model by establishing the relationship between gas concentration and absorption strength. The effect of collision parameters and rotational temperature on the method is also discussed. The proposed method is verified by investigating the nitric oxide emission bands (A²Σ⁺→X²∏) that are generated by a pulsed corona discharge at various gas concentrations. Experiment results coincide well with the expectations, thus confirming the precision and accuracy of the proposed measurement method.

Theoretical and experimental research on recovering line shape with wavelength modulation spectroscopy

Wavelength modulation spectroscopy has not yet formed an efficient method applied to measure line shape, which has restricted the development of tunable diode laser absorption spectroscopy. In the present paper, we have established a method which can recover line shape directly by using the data of the X and Y axes of odd harmonics based on the absorption spectral and harmonic theories. And then, in validating the accuracy of this method, the numerical simulation was used to recover the line shape of the transition at 6527.641cm-1. Meanwhile, the experimental results show that the method established in this paper can recover the line shape accurately.