紫外线分光光度计的光源选择的因素

Light sources used in spectroscopic analysisintroduced you to three broad categories of spectral light sources. Unfortunately there is no single source that is suitable over the entire UV– Visible spectral region (190 -800 nm). Spectrophotometers today come with more than one source with automatic changeover at defined wavelength for optimized and interruption free operation.

The desirable features for light sources are:

Uniform light output over specified wavelength range
Stability of response over extended time periods
Long usage life span
Low-cost

The features of common light sources are reviewed here to help you make your choice:

Deuterium Lamps

d2_lamp — Deuterium Lamps (Image Courtesy : http://www.dot-red.com/)

氘灯是紫外线区域最常见的光源（160 - 375 nm）。通过施加排放，可以在低压下激发氘气的激发，从而产生紫外线辐射，并在真空紫外线区域的应用特种灯中应用至115 nm。气体信封和窗户由石英制成，作为该区域吸收的玻璃。

Deuterium lamps exhibit superior stability in comparison to the Xenon and Mercury- Xenon lamps .Deuterium lamps also have long service life. However, before operation sufficient warm-up time is necessary and a stable power supply is necessary for maintaining a constant current and the temperature of the lamp during operation.

Xenon Sources

XENON_LAMP02 — Xenon lamps (Image Courtesy : http://www.xenon-lamp.com/)

氙气来源覆盖了整个范围可见的范围，甚至超过（160 - 2000 nm）。在其他地区迅速升级的紫外线区域中的排放量很高。此类灯的稳定性低于氘灯。脉冲氙气灯提供了额外的好处，例如减少热量产生，较长的灯光寿命以及由于间歇性暴露而导致样品的衰减减少。

Mercury-Xenon灯包含mixture of Xenon gas and Mercury vapour. Such lamps emit a broad spectrum and include sharp peaks in both UV and visible region corresponding to mercury’s spectral lines. Such lamps have increased utility over xenon lamps due to high output intensity, stability and longer useful life.

Xenon or Mercury- Xenon lamps require warm up time of several minutes and cathode erosion starts affecting lamp stability which, however, can be overcome by using superior cathode materials.

Tungsten Lamps

1319 — Tungsten-Halogen lamps (Image Courtesy : http://assets.newport.com/)

Tungsten filament lamp has been conventionally used as a light source in the visible region covering 350 – 2200 nm. It consists of a thin coiled tungsten filament sealed inside an evacuated glass bulb. Power supply should ensure constant voltage to the lamp for a stable response

Tungsten – halogen lamps consist of a quartz envelope filled with an inert gas and a small amount of halogen such as iodine. Iodine forms tungsten iodide which is volatile in nature.The tungsten iodide molecules decompose on coming in contact with hot filament and redeposit tungsten onto the filament. Tungsten – halogen lamps bring the output closer to the UV region (240-2500 nm) and also extend useful lamp life to almost double of normal tungsten lamp.

It is important to make a judicious choice when deciding on the lamp requirement. You should base your choice on the required wavelength range, intensity requirement, stability, requirement of a stable supply and expected useful life.