Mercury lamps, problems with

The first successful application of the continuous wave (CW) He-Ne gas laser as a Raman excitation source by Kogelnik and Porto (14) was reported in 1963. Since that time, significant improvements in instrumentation have been continually achieved which have circumvented a great number of problems encountered with mercury lamp sources. The renaissance of Raman spectroscopy has also been due to improvements in the design of monochromators and photoelectric recording systems. 

Further barriers to a broader use of Raman spectroscopy are problems with intensity calibration and benchmarking, lack of reference materials, and the expense of the equipment. The calibration equipment, which is typically supplied with the instruments by the manufacturers, varies for instance neon or mercury lamps are delivered with dispersive instruments and HeNe lasers with FT spectrometers. 

A potential problem with light microscopy, especially with high intensity mercury vapor lamps (for blue-violet incident light), is localized sample heating however, for suspensions this phenomenon is generally not as important in creating image artifacts as interactions with the sample holder. 

A problem with this phosphor is that without precautions it usually contains a small amount of unreacted V2O5 which lowers the light output. For application in high-pressure mercury vapor lamps this pho.sphor is usually prepared with an excess of boric acid. The material has then a white body color and, in addition, the particle size can be controlled. The boron is not built into the lattice in some way or another the boron compound acts as a flux. 

Another problem was to choose the most efficient method of exciting salicylic acid, which has only one useful excitation band (at 308 nm). One approach was to use a special phosphor-lamp source emitting between 270 and 340 nm with a peak at 306 nm this gave good sensitivity for salicylic acid. Another approach was to use the somewhat weak 313 nm line emitted by a low-pressure mercury-arc lamp, selected with a combination primary filter consisting of the 7-54 filter along with a plastic filter used to cut out the 254-nm mercury line. This procedure essentially excited only the salicylic acid, not ASA. In both cases, a sharp-cut filter with 37% T at 465 nm was used to exclude any possible emission by ASA. 

Many recyclable materials consist of mixed materials that pose special problems. Discarded automobile oil filters contain steel, fiber, and contaminated petroleum. Oil filters are crushed and heated to remove oil, and the metal reclaimed. Discarded household appliances contain large amoxmts of steel but must often be dismantled, with other materials removed. A special fee is charged at recycling centers to discard most appliances. Fluorescent lamps contain small amounts of mercury that can be reclaimed. Used computers and television sets contain usable materials and, often, some toxic materials that can be collected for safe disposal. 

The imaging performance of poly(vinyl cinnamate) when exposed by a medium-pressure mercury arc lamp is poor. This is due to the mismatch between the absorption spectrum of the cinnamoyl group (with absorbance maximum at 280 nm) and the spectral emission of the mercury arc. The absorption spectrum of poly(vinyl cinnamate) does not overlap with most of the strong emission lines of a mercury arc lamp. This problem can be overcome by spectral sensitization, for example, with the addition of 5% of Michler s ketone, or by the replacement of the cinnamoyl group with a chromophore such as in poly(vinyl cinnamylidene acetate) (IV) that absorbs at longer wavelengths. ... 

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