[Er3+:Yb3+ co-doped nanocrystals BaGd2ZnO5 of up-conversion optical temperature sensing].

By far, the most efficient upconversion nanocrystals luminescence materials BaGd2ZnO5: 4%Yb3+ , 1%Er3+, with stable chemical performance, were prepared by using Sol-gel method. XRD pattern shows that the sample is pure phase, belongs to the orthogonal crystals, and space group is Pbnm; SEM micrograph shows that the prepared sample of the morphology sized around 150 nm is evenly distributed. Samples with 971 nm semiconductor laser excitation produce a strong green emission, visible to the naked eye, and uponversion strength and pump energy relation n = 1.22 is two-photon for the realization of the upconversion emission. They originated from Er3+ ions 2H(11/2)--2H(11/2)-->4I(15/2) and 4S(3/2)-->4I(15/2) transition emission, Er3+ ions main excited state absorption (ESA) process is: 4I(15/2)-->4I(11/2)-->2F(7/2)-->2H(11/2), 4S(3/2), Yb3+ was added because of its large absorption cross section (10(4) cm(-1)) so that it is easy to transfer excitation energy to the E3+ ions which enhance the layout particles number and the energy state of the 1F7/2, thereby enhancing the intensity of the peaks of the spectrum. Fluorescence intensity ratio (FIR) technique based on the green upconversion emission of the sample has been studied because the Er3+ ions 2H(11/2) and 4S(3/2) energy level spacing is small. The electrons at the two levels conform to the Boltzmann distribution which is a function of temperature, and thus the fluorescence intensity ratio of two levels can be used to measure the temperature of the substrate material. This method does not interfere with temperature field of the measured object, and can eliminate the uncertainty of the accuracy; the test has a wide temperature range and reasonable temperature resolution, the pump source used is simple, convenient and inexpensive, and has more commercial values. The temperature range of the samples is from 350 to 800 K, and the highest temperature measuring sensitivity can reach 0.0031 K(1). At the same time, under low excitation density, it can produce higher conversion transmission power, making it become ideal material for distance non-contact temperature measurement.

[Studies on laser induced dispersive fluorescence spectroscopy of SO2 molecule excited by two-photon].

The processes of excitation and complicated de-excitation of A-symmetric state in the first-excited band of SO2 molecule were studied experimentally with the techniques of two-photon laser induced dispersive fluorescence spectroscopy where a pulsed dye laser (579 nm) was used as excitation sources. The SO2 molecule which were excited from ground state X1A1 to the high vibrational levels of A1 A2 state by absorbing two photons, will realize the repopulation in several vibration-rotational energy levels of A1 A2, B1 B1 and alpha3 B1 states by internal energy conversion and collision relaxation. Because of transitions to the different vibrational levels of ground electronic state X1 A1 from the ground vibrational levels of A1 A2, B1 B1, and alpha3 B1, the fluorescence spectrum envelopes centered at 305 and 425 nm and the regular fluorescence lines centered at 347.2 nm were formed in the fluorescence spectra. In addition, the process of tri-photon excitation X1 A1 --> C1 B2 of SO2 molecule was observed, and the result of the process was the fluorescence spectrum envelope in 200-278 nm and the overlapping fluorescence lines centered at 425 nm. The harmonic frequencies of the symmetry stretch vibration and the bendvibration and the anharmonic constants of stretch vibration mode and the bend vibration mode of related states were calculated from the experimental data.

[Mollow profile with seven peaks under double coupling fields].

Transparency and absorption overlaping with Mollow profile in a lambda three-level scheme driven by two coupling fields was investigated. There are two degenerate hyperfine levels within ground state. A strong coupling field and a probing field interact with the same optical transition between the excited state level and the first ground state hyperfine level, and an additional weak coupling field interacts with the excited state level and the second ground state hyperfine level, which is named double coupling lambda three-level scheme. It can be seen that when the strong coupling field is off-resonant, there is the superposition of Mollow profile with EIT, EIA and other quantum coherent phenomena, namely, Mollow profile with seven peaks. The dependence of the position of the EIT or EIA on Rabi frequency and frequency detuning of the strong coupling field was investigated. The results can be accounted for by dressed-state formalism.

[Study on the reaction mechanism of NO removal by pulse corona discharge].

Chemical reaction kinetics of NO removal by pulse corona discharge under the condition of normal atmospheric pressure was studied by using dispersive fluorescence spectrum and time-resomved spectrum. The fluorescence spectrum of NO pulse corona discharge was obtained. Moreover, dactylograms of NO, and those of the N+, O, N2, produced in the process of discharging were confirmed by attributing the fluorescence spectrum, and then the time behaviors of these particles were studied by analyzing these dactylograms. The results show that, the NO molecule turns to NO+ ion after colliding with high-energy electron, and then the NO+ ion breaks down to N+ and O. Subsequently, the N+ ion turns to N atom after absorbing an electron and then combines with another N atom, while the O atom turns to O2 molecule when combining with another O. From these results, the chemical kinetics model of NO removal by pulse corona discharge was proposed, which is helpful to increasing NO removal rate.

[Self-absorption of NO fluorescence induced by two-photon].

The two-photon LIDFS of NO excited with 452.4 nm output of an optical parameter generator and optical parameter amplifier pumped by a Nd: YAG laser was obtained. The vibration frequency and the inharmonic coefficients of the ground electronic state of NO were calculated from the results of the spectral ascription. They are omega"e = (1 904. 7 +/- 7. 3) cm(-1), omega"e chi"e = (14.2 +/- 1.2) cm(-1), and omega"e y"e = -(0.021 8 +/- 0.009 1) cm(-1) respectively. It was found for the first time that the intensity of the spectral lines departs from the Frank-Condon principle due to the self-absorption of NO molecules. The spectral line of A 2sigma (v' = 0) --> X 2 II (v" = 0) transition disappears in the fluorescence spectra. But it appears gradually with decreasing the sample pressure and the distance from the laser-gas interaction volume to the receiving window. All of these provide an important reference for monitoring NO by the technique of laser-induced fluorescence.

[The 440-495 nm laser-induced fluorescence excitation spectrum of NO2].

Under the conditions of room temperature and low pressure, laser-induced fluorescence excitation spectrum of NQ2 in the wavelength region of 440-495 nm was obtained by using optical parameter generator (OPG) and amplifier (OPA) as an excitation source. The OPG/OPA was pumped by a Nd:YAG laser. The peaks of the spectrum are attributed to B2B1 <-- X2A1 transition. The angle-vibration frequency of B2B1 electronic state was calculated. The fluorescence lifetime of B2B1 (0, 9, 0) vibration state under the pressure of 15 Pa was also deduced by measuring the fluorescence time decay spectrum of this state. It is about 49 micros. Fitting the curve the fluorescence radiant lifetime versus pressure, the spontaneous radiant lifetimes tau0 and the rate coefficient kq of non-radiant transition relaxation of B2B1 (0, 9, 0) state are deduced. The results are: tau approximately 55 micros and k(q) = 1.2 x 10(-9) cm3 molecule(-1) s(-1).

[Study on the emission spectrum of B (3)pig state of N2 molecule].

DC glow discharge was used to study N2 molecule at low pressure (4 Torr). The emission spectrum was examined in the range of 320-470 nm in the discharge plasma of N2, which showed that the emission was composed of a series of spectral lines equidistant, and the relative emission intensity became weaker with longer wavelength, whose distribution accorded with Frank-Condon rule. It is attributed to the transition of C 3pi(u)-->B3pi(g). On this base, the authors have calculated the vibrational frequency of B 3pig state to be 1738.50 cm(-1). The Frank-Condon factor about C3pi(u) (v' = 0)-->B3H(g) (v" = 0-5) was calculated, which is consistent with the results of experiment.

[Laser induced dispersed fluorescence spectra of NO2 in the range of 550-740 nm].

Laser induced dispersed fluorescence spectra (LIDFS) of NO2 molecules, excited by second harmonic lines (the output wavelength is 532 nm) of a pulsed Nd: YAG laser at room temperature and at low and high NO2 pressures, were obtained and analyzed. The authors got vibronic progressions in the range of 550-740 nm at low pressure and ascribed them to the transitions from the first excitation electronic state A(2)B2 to the vibrational levels of the ground electronic state X(2)A1, and then calculated the harmonic frequencies of symmetry stretch and bond stretch: omega1 = 1300.72 cm(-1) and omega2 = 744.14 cm(-1), respectively. On the basis of what was above-mentioned, the authors compared the spectra at low pressure with those at high pressure and pointed out the difference between them. Then the authors also interpreted the obvious red shift of fluorescence spectra at high NO2 pressures in terms of a stepladder model of vibrational deactivation and obtained significative results.

[Spectrum of dielectric barrier discharge at atmospheric pressure intensified by mixing a little argon].

In this paper, the spectrum of dielectric barrier discharge at atmospheric pressure was measured by using the special setup with two water electrodes. The variation of spectrum was studied when a little argon was mixed. Nitrogen molecular spectrum (C3 IIu(v' = 0 ) --> B3 IIg(v" = 0-4)) and nitrogen atomic spectrum(4d(4) D7/2 --> 3p(4)P1/2(0)) were found in the range of 300-800nm. After a little argon was mixed, the breakdown voltage of discharge obviously decreased. The spectral line intensities of nitrogen molecules and nitrogen atoms increased. The full width at half maximum (FWHM) of spectral line was obviously broadened. Because Stark broadening is a linear function of electron density, it can be seen that electron density increased after a little argon was mixed with the air, which caused the probability of excitation collision of N2 and N with electrons to increase, and the number of N2 and N excited to higher excitation state to increase. So the intensity of spectrum was intensified.

[Mechanism of resonance-enhanced multiphoton ionization of NO molecule].

NO molecule is a diatomic molecule with different nucleus. It is a serious pollutant and is harmful to the health of the generation. It comes mainly from inflammation process using coal as burning material. So researchers have always been interested in it. The Resonance-Enhanced Multi-Photon Ionization (REMPI) spectrum of NO has been obtained in the range of 420-480 nm with a Nd:YAG laser pumped optical parametric generator and amplifier as the radiation source. The ionization pathway of NO molecule was acquired with the assignment of the spectral lines. NO molecules are ionized via the resonant intermediate state A2 sigma+ and by a (2 + 2) REMPI process. On the basis of theoretical rate equation and with the condition that the duration of the laser pulse is very short (approximately 35ps), the dependence of ion signals on laser intensity was deduced. The variation of the ionization signal versus laser intensity is near quartic. This is in good agreement with the experimental result.

[Laser fluorescence excited spectrum of NO via alpha2sigma<--chi2pi transition].

Two-photon fluorescence excited spectrum of NO induced by Nd: YAG laser pumped optical parameter generator/amplifier as excitation source was obtained in the range of 420-472 nm. With this technique, the structure of the energy levels of NO molecule in alpha2sigma electronic state was investigated. The peaks of the spectrum were attributed to alpha2sigma(v' = 0,1)<--chi2pi(v" = 0) transition. The near square dependence of fluorescence signal on the laser intensity indicates a two-photon process. The ground-vibrational-state oscillation frequency and the force constant of alpha2sigma state were calculated. The fluorescence lifetime of alpha2sigma(v' = 0) state under the pressure of 266 Pa was also obtained by measuring fluorescence decay curve of alpha2sigma(v' = 0) states. It is about 53.76 ns. Fitting the curve of the fluorescence radiant lifetime versus pressure, the spontaneous radiant lifetimes and the rate coefficient of nonradiative transition relaxation of alpha2sigma(v' = 0,1) states were deduced.

[Resonance-enhanced multiphoton ionization spectrum of NO by D2 sigma state].

NO is an important pollutant molecule, and plays a key role in generating photochemical smog and destroying O3 in the atmosphere. So researchers have always been interested in it. In our experiment, the optical parameter generator and amplifier (EKSPLA) pumped by Nd:YAG (Quantel) laser were used as the radiation source. The REMPI spectrum of NO in the region of 460-570 nm was obtained. Based on theoretical calculation, most of the lines were attributed to the X2 pi --> D2 sigma transition. The ionization pathway was discussed in detail, which can be shown as NO(X2 pi) (3h nu)--> NO(D2 sigma) (2h nu)--> NO+ + e. The vibration fundamental and force constant of NO (D2 sigma) state were calculated. The results are omega(e) = 2339.2 cm(-1) and k = 2.41 x 10(5) dyn x cm(-1). For future work, the resolution of the radiation source will be improved in order to obtain more information of the D2 sigma state.

[Study on the formation of XeCl at low pressure].

Low pressure dielectric barrier discharge was used to study the formation of XeCl excimer in a mixture of Xe/Cl2 in the range of 70-1,330 Pa. The fluorescence emission spectra in the range of 285-315 nm at different pressure and ratio of Xe/Cl2 were measured. The results indicate that near 308 nm the emission intensities of XeCl formed under the experimental conditions varied with different total pressure and ratio of Xe/Cl2, and the formation efficiency of XeCl excimer reached maximum value at the ratio of 4:1.

[The fluorescence emission spectrum of NO in dielectric barrier discharge (DBD) plasma].

Dielectric barrier discharge was used to study the NO molecules of the atmosphere pollution, and the fluorescence emission spectrum in the range of 210-280 nm at low pressure was obtained in this plasma. The spectrum shows obviously the structure of double apices, whose intensity distribution in accord with Frank-Condon principle and the maximum lies at 236 nm. The main lines are attributed to the A 2 sigma+ -->X 2 pi 1/2, 2/3 transition. The produce of fluorescence can be described as: NO molecules at the ground state are impacted to the A 2 sigma+ excited state by fast electrons, and then transit to the ground state radiating fluorescence. By measuring the relation between discharge time and emission intensity of NO and N2 molecules in the discharge plasma, we demonstrated the dissociation mechanism of NO in the discharge period, which can be interpreted as: e* + NO-->N + O + e, N + NO-->N2 + O, O + NO-->NO2 + h nu.

[Spectroscopic diagnoses of glow discharge plasma for the carbon nitride growth process].

Plasma diagnostics is performed during dc. glow discharge plasma-enhanced chemical vapor deposition (PECVD) on nitride thin films using optical emission spectra. Several molecular bands such as the second positive series of N2 transitions, the first negative series of N2+ and the CN, NH violet bands are identified. Variations of the emission intensities of N2(337.1 nm), N2+(391.4 nm) and CN(388.3 nm) are investigated as the function of the percentage of H2, discharge current and deposition pressure. The related excitation mechanism of the species emission is discussed. Experimental results show that adding a small amount of H2(about 5%) into the gas source will be beneficial to produce all the active species. Higher discharge current will result in an increase of the active species concentration while there is maximum emission intensity at medium gas pressure at about 4 kPa. The collisions between the species, including metastable nitrogen and hydrogen are related with the concentration variations of the measured species. All the results and discussion provide reference data for optimizing the deposition parameters and controlling the deposition process in the synthesis of carbon nitride thin films.