Colour centre

Defects in a crystal lattice that absorb certain wavelengths of light

Introduction

A colour centre (or color center) is a defect in a crystal lattice that absorbs certain wavelengths of light, giving the crystal a characteristic color. These defects are typically vacancies or impurities in the crystal structure that alter the electronic properties of the material, allowing it to absorb visible light.

Types of Colour Centres

Colour centres can be classified based on the nature of the defect and the type of crystal in which they occur. Some common types include:

F-centres

An F-centre (from the German "Farbe" meaning "color") is a type of colour centre that occurs when an anion vacancy in a crystal lattice is occupied by one or more electrons. This type of defect is common in alkali halides such as sodium chloride and potassium chloride. The presence of these electrons in the vacancy allows the crystal to absorb light in the visible spectrum, resulting in a color change.

V-centres

V-centres are another type of colour centre, which involve the presence of a vacancy associated with a missing cation. These centres can also trap electrons, leading to absorption of light and coloration of the crystal.

Other Centres

Other types of colour centres include M-centres, R-centres, and N-centres, each with unique characteristics and occurring in different types of crystals. These centres can involve complex interactions between vacancies, impurities, and trapped electrons.

Formation of Colour Centres

Colour centres can form naturally or be induced artificially. Natural formation occurs due to imperfections in the crystal growth process or exposure to radiation. Artificial induction can be achieved through methods such as:

• Irradiation: Exposing the crystal to high-energy radiation, such as X-rays or gamma rays, can create vacancies and displace atoms, leading to the formation of colour centres.
• Doping: Introducing impurities into the crystal lattice can create vacancies or alter the electronic structure, resulting in colour centres.

Applications

Colour centres have several practical applications due to their unique optical properties:

• Lasers: Certain colour centres can be used as active media in solid-state lasers, where they provide the necessary energy levels for laser action.
• Optical Filters: The ability of colour centres to absorb specific wavelengths makes them useful in creating optical filters for various applications.
• Quantum Computing: Colour centres, such as those found in diamond, are being explored for use in quantum computing due to their stable electronic states and ability to interact with light.

Visual Representation

Diagram illustrating the process of colour centre formation in a crystal.

Visual field maps showing the effect of colour centres on light absorption.

Animation of the lingual gyrus, an area of the brain involved in visual processing.

Animation of the fusiform gyrus, another brain region related to visual perception.

Functional magnetic resonance imaging used to study brain activity related to visual processing.

Bilateral representation of brain regions involved in processing visual information.

Related Pages

• Crystal defect
• Solid-state physics
• Optical properties of materials
• Quantum dot