Currently, the method of choice to test for the presence of chromium in water is to submit samples to a lab for testing. We present a simple field-ready test that is selective for the presence of chromium at concentrations of 100 ppb or greater. The Environmental Protection Agency maximum contaminant level (MCL) for total chromium is 100 ppb. This test uses a simple on/off fluorescent screening employing the use of silver indium sulfide (AgInS2) quantum dots (QDs). These QDs were impregnated into cotton pads to simplify field testing without the need for solvents or other liquid chemicals to be present. The change in fluorescence is instant and can be readily observed by eye with the use of a UV flashlight.
We present previously unreported properties of the organic molecular dye compound, 2,3,7,8-tetracyano-5,10-dimethyl-5,10-dihydrodipyrazino[2,3-b:2’,3’-e]pyrazine (DMTC-pyrazine) (CAS Reg. No. 150960-11-5), including photophysical properties with particular emphasis on optical waveguiding. We show that DMTC-pyrazine can self-assemble into monoclinic crystals that are thermally stable over 300°C. Through shape-engineering, optimized growth conditions produced high yields of nanofiber (aspect ratio >6) crystals. No photobleaching of this dye was observed in air even after hours of on-resonant illumination. Excitation of photoluminescence within the DMTC-pyrazine nanofibers propagates in tightly confined guided modes (up to 25 μm). The finesse, end-facet reflectance, and group refractive index of nanofiber DMTC-pyrazine Fabry-Pérot cavities are reported.
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