直读光谱仪的理论基础-光能激发

The spectrum emitted by atoms is known as the “emission spectrum”. If the required energy is supplied in the form of white light, energy at specific wavelengths may be removed for excitation. These wavelengths correspond to the discrete differences in permitted energy states in the atomic shell. Accordingly, absorption lines in the form of dark lines on a continuous background appear in the spectral equipment at those wavelengths which are “swallowed” by the atom. This is the basis of AAS. Substances can only absorb light at the same wavelength as they are capable of emitting . For example , excited sodium vapour emits yellow light, but if we look through sodium vapour it seems purple since it lets through everything from the white light except yellow and it shows the colour complementary to yellow.

The portion of white light absorbed by the sodium vapour is scattered in all directions in the form of a yellow fluorescence radiation. This is the basis AFS.

In the same way, some substance can become fluorescent as a result of irradiation. For this it is not necessary, as in the case of sodium vapour, that only individual wavelengths should be emitted. The excited atom can return to the ground state through the radiation of a number of frequencies. The frequencies are smaller than those of exciting absorbed radiation. The fluorescence may not fade quickly- as with gases and vapours –but slowly. This kind of “ slow fluorescence” is shown by some solid material eg. calcium sulphide.

原子发出的光谱称为“发射光谱”。如果所需的能量以白光的形式提供，特定波长的能量可能会被激发。这些波长对应于原子壳层中允许能态的离散差异。因此，在被原子“吞噬”的波长的光谱设备中，在连续的背景上以暗线的形式出现吸收线。这是AAS的基础。物质只能吸收它们所能发射的相同波长的光。例如，被激发的钠蒸汽会发出黄色的光，但如果我们透过钠蒸汽，它看起来是紫色的，因为除了黄色外，它能透过所有的白光，它显示出与黄色互补的颜色。

钠蒸气吸收的那部分白光以黄色荧光辐射的形式向四面八方散射。这是AFS的基础。

同样，有些物质也会因为辐射而变成荧光物质。因此，不需要像钠蒸汽那样，只发射单个波长的光。受激原子可以通过一定频率的辐射回到基态。频率比那些令人兴奋的吸收辐射要小。这种荧光可能不会像气体和蒸汽那样很快消失，但会慢慢消失。这种“慢荧光”是由一些固体材料如石墨烯等表现出来的。硫化钙。