Photonics Dictionary

emission spectrum

An emission spectrum is a graphical representation or a characteristic pattern of the wavelengths or frequencies of light emitted by a source, such as an atom, molecule, or celestial object. It shows the distribution of emitted light across the electromagnetic spectrum. This spectrum is unique to the emitting substance and is often used in analytical chemistry, astrophysics, and other scientific fields for identifying elements or compounds based on their distinctive spectral lines.

Key points about emission spectra include:

Emission lines: An emission spectrum typically consists of discrete lines or bands of light at specific wavelengths. Each line corresponds to a particular energy transition within the emitting system, such as the movement of electrons between energy levels in an atom.

Excitation and de-excitation: The emission spectrum is produced when atoms or molecules undergo excitation, absorbing energy, and subsequently return to lower energy states, emitting photons in the process. The emitted photons create the observed spectral lines.

Continuous and line emission spectra: There are two main types of emission spectra. A continuous emission spectrum spans a broad range of wavelengths without distinct lines, often produced by hot, dense objects. Line emission spectra, on the other hand, exhibit specific, discrete lines corresponding to the emission of photons at particular wavelengths.

Identification of elements: Emission spectra are used to identify elements and compounds. Each element has a unique set of spectral lines, allowing scientists to determine the composition of a sample by analyzing its emission spectrum.

Applications: Emission spectra play a crucial role in various scientific fields. In astronomy, the analysis of the light emitted by stars and galaxies helps astronomers understand their composition and temperature. In analytical chemistry, emission spectroscopy is used for elemental analysis.

Flame test: In a simple laboratory demonstration, the flame test involves observing the emission spectrum of elements in a flame. Different elements emit characteristic colors when heated in a flame, providing a qualitative identification.
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