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level: Causes of colour

Questions and Answers List

level questions: Causes of colour

Question	Answer
What are the five major causes of colour in gemstones?	Dispersed metal ions
What happens when an electron absorbs electromagnetic radiation energy, causing it to jump to a higher energy level, then return to its original state?	Energy is released
When energy is released from an electron into the crystal structure of the gem material, what two forms can it take?	Atomic vibrations (Heat)
What is the name for the chemical elements in gemstones that interact with light energy to produce absorption, which results in the perception of body colour?	Transition elements
What do the transition elements form, that are dispersed throughout the crystal structure of a gestone, producing different colours?	Metal ions
What is it that surrounds a transition ion in a gem material, that causes different colours in different materials, despite the transition ion being the same?	Oxygen ions
What else can be cause of different colour seen in different gem materials, that have the same transition ion and the same amount of oxygen ions?	Crystal structure
What is the term used to describe energy release from electrons in certain gem materials visible in the form of light, that can be seen under ultraviolet light?	Luminescence
What is the term used to describe the transfer of an electrical charge between one ion and another, in the form of a negatively charged electron?	Charge transfer
Charge transfer efficiency permits much stronger absorption than dispersed metal ions, which results in...... ?	Stronger colours
What is the term used to describe the charge transfer between two metal ions that are separated by an oxygen atom, that is constantly going back and forth?	Metal-to-metal
What is the name of defects in a crystals structure that absorb light?	Colour centres
What type of colour centre is created when a hole exists within the crystal structure?	Vacancy
What type of colour centre is created when an electron is displaced from its original orbit, and can be reversed by heating?	Hole
What type of colour centre is created when a vacancy is created within a crystal structure, that is then filled by an electron?	Electron
What type of colour centre caused the yellow colour in diamonds, and is caused by a vacancy in the diamonds carbon structure being surrounded by three notrogen atoms?	Vibronic
In some gem materials, there are electrons that are in a fixed position, tied to atoms and ions, and some with a higher energy level that are able to move throughout the crystal structure. What is the name for the difference in energy levels between these electrons?	Band Gap
In relation to the visible light spectrum, what three types of band gap are visible in certain gem materials?	Larger
What colour are materials with a large band gap, due to the fact visible light is unable to react with the electrons, so no light is absorbed?	Colourless
What do gem materials with a small band gap look like, due to the fact all visible light is absorbed?	Opaque
What causes colour in diamond, an otherwise colourless stone, by occupying the large band gap in the form of additional electron energy levels?	Chemical impurities
What is the name for the type of colour caused by thin films within the stone that can be solid, liquid, different types of solid and cavities such as cracks, causing a double reflection of light waves?	Thin-film inteference
What is the term used to describe two reflected rays of light travelling in the same direction within a close space caused by thin-film inteference, specifically when the wave peaks and troughs coincide?	In phase
What is the term used to describe two reflected rays of light travelling in the same direction within a close space caused by thin-film inteference, specifically when the wave peakof one coincides with the trough of another?	Out of phase
What is the term used to describe light being randomly reflected by particles within a gem material?	Scattering
What is the name of the material particles that causes the scattering of light within a moonstone	Albite
The play of colour in opals is caused by regularly stacked, three dimensional groups of spheres of what material?	Silica
The gaps between the microscopic silica spheres in opal provide small apertures that cause what?	Diffraction