In the traditional fluorescence detection, samples are tested in the solvent, and the mutual effect of solvent, micro impurity and sample affects the fluorescence characteristics. Meanwhile, such effect includes vibrational relaxation, electron rearrangement of solvent molecule, special role of the sample with the solvent molecules and so on. The experiment of fluorescence quantum efficiency at atmosphere reduces the interference, because the distance between molecules is much larger in gas phase. In addition, the research of quantum efficiency can also promote the understanding of LIF and expand the range.
In this paper, the fluorescence quantum efficiency of 3 different samples at atmosphere was compared, and the electrospray ionization source was selected for its soft ionization characteristics. The ionization method did not spoil the fluorophore of the sample, and the drift tube of ion mobility spectrometry (IMS) was used for ions transport and desolvation. The ionization source was on the one side of the drift tube and the test point was on the other side. The paths of excited laser and emission light were orthogonal at the test point. Meanwhile, stable ions flowed through the drift tube. The emission light was captured by the camera, which was coupled with a long-wave pass filter. The test samples were Rhodamine 6G，Rhodamine B and amino copper indium sulfide quantum dots of the same mass fraction. The energy of excited laser was between 30 mW and 150 mW. Then the results showed that the emission intensity was proportional to the laser power in gas phase, and the sort of the fluorescence quantum efficiency was the quantum dots>Rhodamine 6G>Rhodamine B.
Ion Mobility Spectrometry (IMS), having an advantage in real-time and on-line detection, is an atmospheric pressure detecting technique. LA-IMS (Laser Ablation Ion Mobility Spectrometry) uses Nd-YAG laser as ionization source, whose energy is high enough to ionize metal.
In this work, we tested the signal in different electric field intensity by a home-made ion mobility spectrometer, using silicon wafers the sample. The transportation of metal ions was match with the formula: Td = d/K • 1/E, when the electric field intensity is greater than 350v/cm. The relationship between signal intensity and collection angle (the angle between drift tube and the surface of the sample) was studied. With the increasing of the collection angle, signal intensity had a significant increase; while the variation of incident angle of the laser had no significant influence. The signal intensity had a 140% increase when the collection angle varied from 0 to 45 degree, while the angle between the drift tube and incident laser beam keeping the same as 90 degree. The position of ion gate in LA-IMS(Laser Ablation Ion Mobility Spectrometry) is different from the traditional ones for the kinetic energy of the ions is too big, if the distance between ion gate and sampling points less than 2.5cm the ion gate will not work, the ions could go through ion gate when it closed. The SNR had been improved by define the signal when the ion gate is closed as background signal, the signal noise including shock wave and electrical field perturbation produced during the interaction between laser beam and samples is eliminated when the signal that the ion gate opened minus the background signal.