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Molecular images of documents were obtained by sequentially scanning the surface of the document using desorption atmospheric pressure chemical ionization mass spectrometry (DAPCI-MS), which was operated in either a gasless, solvent-free or methanol vapor-assisted mode. The decay process of the ink used for handwriting was monitored by following the signal intensities recorded by DAPCI-MS. Handwritings made using four types of inks on four kinds of paper surfaces were tested. By studying the dynamic decay of the inks, DAPCI-MS imaging differentiated a 10-min old from two 4 h old samples. Non-destructive forensic analysis of forged signatures either handwritten or computer-assisted was achieved according to the difference of the contour in DAPCI images, which was attributed to the strength personalized by different writers. Distinction of the order of writing/stamping on documents and detection of illegal printings were accomplished with a spatial resolution of about 140 μm. A Matlab® written program was developed to facilitate the visualization of the similarity between signature images obtained by DAPCI-MS. The experimental results show that DAPCI-MS imaging provides rich information at the molecular level and thus can be used for the reliable document analysis in forensic applications.

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Transition-metal tetravalent manganese ions (Mn) as luminescence center of red phosphors have drawn much attention owing to their broad-band absorption extended from UV to blue regions and narrow red-emissive band. In the present work, a series of Mn-doped BaGeF red phosphors were obtained via hydrothermal method. X-ray powder diffraction, energy-dispersive X-ray spectrometer, scanning electron microscope, and photoluminescence spectra were employed to determine the crystal structure, composition, morphology, and photoluminescence properties of all samples. The prepared BaGeF:Mn samples demonstrate two dominant broadband absorption at near-UV (∼366 nm) and blue regions (∼470 nm) and intense red emissions (∼635 nm) under 470 nm excitation. In addition, the morphology and the emission intensities were successfully controlled by adjusting doping concentrations, reaction times, reaction temperatures, barium sources, and surfactants. Concentration quenching and thermal quenching mechanisms were studied in detail. When the BaGeF:Mn red phosphor was introduced into the light-emitting diode, warm white light-emitting diodes (w-LEDs) were successfully fabricated, which have high color rendering index (Ra = 86.3) and low correlated color temperature (4766 K), indicating that the BaGeF:Mn red phosphor provides a good opportunity for application in w-LEDs.

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