There are a number of ways in which atoms can be brought to an excited state. Photoexcitation, happen when an electron absorbs a photon and gains the photon's energy. Electrons can also be excited by electrical excitation, where the original electron absorbs the energy of another, energetic electron. The simplest method is to heat the sample to a high temperature. The thermal energy produces collisions between the sample atoms causing the atom's electrons to be excited.
When an excited electron falls back to a lower energy state again, it is called electron relaxation. The resulting emission spectrum can be used to determine the composition of a material, since it is different for each element of the periodic table.
One example is astronomical spectroscopy:
identifying the composition of stars by analysing the received light. The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a strontium nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when copper is inserted into a flame, the flame becomes green.
These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all lights emitted by the spectrum are viewable to the naked eye, it also includes ultra violet rays and infra red lighting, an emission is formed when an excited gas is viewed directly though a spectroscope.
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