Challenge and study for developing of novel single crystalline optical materials using micro-pulling-down method Akira Yoshikawa a, * , Martin Nikl b,d , Georges Boulon c , Tsuguo Fukuda a a Institute of Multidiscipliunary Research for Advanced Materials, Tohoku University, Katahira 2-1-1 Aoba-ku, Sendai 980-8577, Japan b Institute of Physics, AS CR, Cukrovarnicka ´ 10, 162 53 Prague, Czech Republic c Physical Chemistry of Luminescent Materials, Claude Bernard/Lyon 1 University, UMR 5620 CNRS, Villeurbanne, France d Dip. Scienza dei Materiali, Universita di Milano-Bicocca, via Cozzi 53, 20125 Milano, Italy Available online 31 January 2007 Abstract Micro-pulling-down (l-PD) method is a useful tool to search for new materials. This method allows us to prepare single crystalline materials quickly and relatively inexpensively. Grown crystals are of sufficient dimensions for all the necessary characterization by optical and luminescence methods, including photo- and radio-luminescence, decay kinetics and light yield measurements. Recent results obtained for laser and scintillator materials at Pr-doped Y 3 Al 5 O 12 , Lu 3 Al 5 O 12 , YAlO 3 ,Y 2 SiO 5 , Lu 2 SiO 5 , fluorides like Ce-doped PrF 3 , mixed binary fluorides AEF 2 –REF 3 , (Ce:AE:(Gd,Y)F 3 , AE = Ba, Sr, Ca) and Yb- and Tm-doped RE 2 O 3 (RE = Y, Lu, Sc) are summarized here. Practical importance of l-PD method follows also from the shaped crystal growth aspect. It is possible to grow shaped and/or device-size crystals from the melt using a single step process. Recent improvement of l-PD method makes the quality of l-PD crystals comparable with those prepared by Czochralski (Cz), Bridgeman, or other classical growth techniques. Ó 2006 Elsevier B.V. All rights reserved. Keywords: Crystal growth from the melt; Oxide; Fluoride; Luminescence; Emission; Decay time; Laser; Scintillator; Micro-pulling-down method 1. Introduction Study of emission centers in different crystal host is an active area of the research, which is addressed by many researchers. Thus, understanding of driving factors of the optical processes in the crystals with different concentra- tions of dopants are often needed. Interaction between dopant ions and lattice phonons, asymmetric crystal field perturbations or the energy transfer processes are typical examples on which the research effort is focused. Further- more, the distribution of the dopant ions in the crystals is very important factor to determine the spectral and tempo- ral properties of the emission [1,2]. For this purpose, we need crystals with variety of dopant concentrations having similar (high) crystalline perfection. The micro-pulling-down (l-PD) method allows growing a single crystal using small amount of row material, typi- cally less than 1 g, in 5–12 h because of very high growth speed typically 0.05–1 mm/min. This very high growth speed makes the l-PD method the unique tool for single crystalline materials screening. The l-PD is melt growth technique and can be catego- rized as one of the shaped crystal growth methods, so called Stepanov method [3]. In the case of l-PD, crucible plays an important role. It is not only container of the melt but also the shaper (die) for the shaped crystal growth. Therefore, the possibility of producing device-size matched crystals in the form of fibers, rod-, plate- and tube-shaped elements to reduce the loss due to machining is also the advantage of this system. The l-PD method was proposed by Dr. Ohnishi at the Electrotechnical Laboratory, in Tsukuba, Japan and established at the Fukuda Laboratory, Institute of Materi- als Research, Tohoku University in Sendai, Japan [4,5]. 0925-3467/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2006.10.030 * Corresponding author. Fax: +81 22 217 5102. E-mail address: yosikawa@tagen.tohoku.ac.jp (A. Yoshikawa). www.elsevier.com/locate/optmat Optical Materials 30 (2007) 6–10