Exploration On Crystal Growth And Quality Improved Of Fluoride Crystal Bay₂f₈

As an excellent laser crystal, the fluoride crystal BaY2F8 has many outstanding merits comparing with other laser crystals, such as lower phonon-energy, lower refracting power and easy to be doped with rare earth ions. The BaY2F8 crystal doped with different rare earth ions emits different wave band lights, which could be used in different laser systems with kinds of applications. The exploration on crystal growth and physical properties of pure BaY2F8 crystal would provide some valuable information for the preparation and exploration of Re: BaY2F8 crystals, accrodingly, it is necessary to grow pure BaY2F8 crystal. According to the reports, most of the crystals BaY2F8 were grown by C-Z method. In this paper we have successfully grown the pure BaY2F8 crystals by the temperature gradient technique method.Using bond-theory, we give an explaination of why pure BaY2F8 crystal would crack more easily than the Er: BaY2F8 crystal does. When the Er enters the BaY2F8 crystal, it will replace Y. The result is that part of the F-Y bond becomes the F-Er bond. Because of ionic polarization, the F-Er bond will be much stronger than the F-Y bond, therefore the Er: BaY2F8 crystal could sustain much bigger stress than the BaY2F8 crystal. In order to get BaY2F8 crystal without cracking, we must improve the technics based on the growth of the Er: BaY2F8 crystal.Based on the practices, the following suggestions are given to improve the quality of BaY2F8 crystal:Firstly, we can grow the BaY2F8 crystal with smaller temperature gradient.The BaY2F8 crystal which is got by smaller temperature gradient has smaller heat stress. It is an effective solution to avoid cracking.Secondly, the crucible is made of better quality graphite material.If the graphite material volatiles seriously, it will lead to Lattice distortion.Finaly, we should try our best to make the radial direction temperature horizontal.