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Related Concept Videos

Imperfections in Crystal Structure: Stoichiometric Point Defects01:26

Imperfections in Crystal Structure: Stoichiometric Point Defects

Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...
Imperfections in Crystal Structure: Point, Line and Plane Defects01:25

Imperfections in Crystal Structure: Point, Line and Plane Defects

A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...
Imperfections in Crystal Structure: Non-Stoichiometric Defects01:29

Imperfections in Crystal Structure: Non-Stoichiometric Defects

Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...
Crystal Field Theory - Octahedral Complexes02:58

Crystal Field Theory - Octahedral Complexes

Crystal Field Theory
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
Crystal Field Theory - Tetrahedral and Square Planar Complexes02:46

Crystal Field Theory - Tetrahedral and Square Planar Complexes

Tetrahedral Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
Crystallographic Point Groups01:29

Crystallographic Point Groups

Crystallographic point groups represent the various symmetry operations that can occur within crystals. They are unique in that at least one point will always remain unchanged during these actions. For instance, consider the triclinic system. This system, devoid of any axis or plane of symmetry, aligns with the C1 and Ci point groups.where Cᵢ is characterized solely by a center of inversion.Contrastingly, the monoclinic system introduces an element of symmetry. This system with one plane and...

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High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
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Properties of optically active vacancy clusters in type IIa diamond.

J-M Mäki1, F Tuomisto, C J Kelly

  • 1Department of Applied Physics, Helsinki University of Technology, 02150 TKK, Finland.

Journal of Physics. Condensed Matter : an Institute of Physics Journal
|August 12, 2011
PubMed
Summary

Brown diamond

Area of Science:

  • Materials Science
  • Solid State Physics
  • Defect Physics

Background:

  • Natural diamonds exhibit color variations, with brown coloration often linked to specific defects.
  • Understanding these defects is crucial for diamond characterization and treatment.
  • Previous studies suggest vacancy-related defects influence diamond color.

Purpose of the Study:

  • To investigate the nature of defects responsible for the brown color in natural diamonds.
  • To correlate optical properties with vacancy defect structures.
  • To examine the effect of high-pressure, high-temperature (HPHT) treatment on these defects and color.

Main Methods:

  • Positron lifetime spectroscopy was employed to analyze vacancy defects.
  • Monochromatic illumination was used in conjunction with positron measurements.

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  • Optical absorption spectra were recorded for comparison.
  • Samples included brown natural diamond, HPHT-treated colorless diamond, and naturally colorless type IIa diamond.

    • Main Results:

    • Brown diamonds contain optically active vacancy clusters (40-60 missing atoms).
    • These clusters show photo-excitation induced charge changes (neutral to negative).
    • Vacancy clusters correlate strongly with optical absorption spectra.
    • HPHT treatment, especially at 2500°C, reduces and eventually removes these clusters.
    • Treated samples become optically similar to colorless diamonds with comparable positron lifetimes.

    Conclusions:

    • The study identifies specific vacancy clusters as the origin of brown coloration in natural diamonds.
    • The optical activity of these clusters is linked to their charge state.
    • High-pressure, high-temperature treatment effectively removes these color-causing defects, leading to decolorization.