Verteilung von Aktivatoren in Laser‐Kristallen

Abstract

Es wird der EinfluB der Ziichtungsbedingungen auf den Verteilungskoeffizienten und auf die radiale Verteilung von Aktivatoren in Rubinen und Yttrium-AluminiumGranaten beschrieben. Der Verteilungskoeffizient von Chrom hiingt vor allem von der Zusammensetzung der Ziichtungsatmosphiire ab, wahrend von ihr der Verteilungskoeffizient von Neodym unabhiingig ist. Der Gradient der Aktivatorkonzentration im Querschnitt der Kristalle ist der mit der Phasengrenze parallelen Komponente des Temperaturgradienten proportional. Die Form der Phasengrenze der nach der Czochralski-Methode gezuchteten Kristalle padt sich der Form der Isothermen in der Schmelze an und die mit der Phasengrenze parallele Komponente des Temperaturgradienten ist vernachliissigbar. Die Phasengrenze der nach der Verneuil-Methode geziichteten Kristalle ist gewohnlich unabhiingig von der Form der Isothermen.The influence of growth conditions on the distribution coefficient and the radial distribution of activators in rubies and in neodynium doped yttrium-aluminium garnets is described. The distribution coefficient of chromium depends upon the composition of the growth atmosphere, whereas the distribution coefficient of neodymium is independent on it. The radial gradient of the activator concentration is proportional to the component of temperature gradient which is parallel to the phase interface. The shape of the phase interface of Czochralski-grown crystals conforms t o the form of the isotherms, whereas of Verneuil-grown crystals is usually flat.

On the effect of oxygen partial pressure on the chromium distribution coefficient in melt-grown ruby crystals

“…In good quantitative agreement with the experimental results, k 0 > 1 for moderate oxygen pressure, and k 0 < 1 for very low oxygen pressure. Similar observation was made by Kvapil et al [2]. In their Czochralski grown crystals they found a distribution coefficient ranging between 0.2 in a reducing atmosphere (Ar with 2% H 2 ), and a maximum of 1.2 for a slightly oxidizing atmosphere (N 2 with 1...2% O 2 2 ).…”

“…Various techniques have been used to grow ruby single crystals including the Czochralski [1][2][3][4], Verneuil [2,[5][6][7] and other melt growth techniques [8][9][10][11], the hydrothermal method [12,13], high-temperature solution (flux) growth [14][15][16][17], and growth from the gas phase [18]. However, reports on chromium segregation are only rarely found in the literature and the values of the distribution coefficient given by different groups vary in a wide range [2,10,11,19].…”

“…Various techniques have been used to grow ruby single crystals including the Czochralski [1][2][3][4], Verneuil [2,[5][6][7] and other melt growth techniques [8][9][10][11], the hydrothermal method [12,13], high-temperature solution (flux) growth [14][15][16][17], and growth from the gas phase [18]. However, reports on chromium segregation are only rarely found in the literature and the values of the distribution coefficient given by different groups vary in a wide range [2,10,11,19]. For the Czochralski and Verneuil techniques it was found [2] that the chromium distribution coefficient drastically changes with growth atmosphere, from less than 1 in a virtually oxygen-free atmosphere to greater than 1 in an oxygen containing atmosphere.…”

“…However, reports on chromium segregation are only rarely found in the literature and the values of the distribution coefficient given by different groups vary in a wide range [2,10,11,19]. For the Czochralski and Verneuil techniques it was found [2] that the chromium distribution coefficient drastically changes with growth atmosphere, from less than 1 in a virtually oxygen-free atmosphere to greater than 1 in an oxygen containing atmosphere. It is suggested that this effect is caused by changes in the chromium valence.…”

Application of predominance diagrams in melt growth of oxides

“…This explains why ruby can be grown at adequate quality without special care for the atmosphere. However, it has been observed [14] that chromium segregation coefficient varies with p O2 , and suggested that this behaviour is linked with a change in chromium valency. Indeed, at very low p O2 and high temperatures, chromium(II) oxide (CrO), may be formed.…”