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Chemical segregation in micro-pulling-down process: analytical model and experiments

Abdeldjalil Nehari 1Thierry Duffar 2Kheirreddine Lebbou 1

1. Institut Matière et Lumière Université Lyon (CNRS), Villeurbanne cedex 69622, France
2. SIMaP EPM, CNRS UJF, BP 75, Saint Martin d'Heres cedex 38402, France

The micro-pulling down (µ-PD) process consists in pulling a crystal under a capillary channel placed at the bottom of a crucible. In spite of the fact that it is limited to rather small liquid volumes, it is used to grow single crystal fibers  and shaped crystals of various cross sections, mainly applied industrially for optical applications such as lasers, optics or scintillators. Consequently those crystals should be doped with active elements in order to fit the target application. Unfortunately, whatever the growth parameters and the dopant type, quite often segregation problem is observed.  It is generally believed that chemical segregations in µ-PD technique are restricted to the first grown millimeters, but some experiments show that it is not always the case.

An analytical one dimensional model is presented, aiming to predict the longitudinal segregation along the growth direction. It is shown that it depends in practice on growth parameters such as capillary length, meniscus height, crucible volume and growth rate. The characteristic numbers controlling the type of segregation that will be obtained are derived and a parametric study is performed in the case of Ti-doped sapphire single crystal fibers.

Such Ti:Al2O3 single crystal fibers oriented along c-axis have been grown under stationary stable regime using different pulling rates and the longitudinal chemical segregation has been characterized by photoluminescence. Results are in agreement with the model predictions.


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Related papers

Presentation: Oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, General Session 2, by Thierry Duffar
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-12 18:49
Revised:   2013-07-23 16:50