791 Table 1. Glass Compositions mass Studied 791 Journal of the Ceramic Society of Japan 114 [9] 791–794 (2006) Technical report ^Äëçêéíáçå ~åÇ bãáëëáçå péÉÅíê~ çÑ káaçéÉÇ dä~ëëÉë ~åÇ dä~ëë`Éê~ãáÅë áå `çååÉÅíáçå ïáíÜ fíë `çlêÇáå~íáçå kìãÄÉê Ni ˁӏêďñʃêďñÊñĆíúđ Sasithorn KHONTHON, Shigeki MORIMOTO and Yasutake OHISHIಓ School of Ceramic Engineering, Institute of Engineering, Suranaree University of Technology, 111 University Avenue, Muang District, Nakhon Ratchasima 30000, Thailand ಓ Department of Future-oriented Basic Science and Materials, Toyota Technological Institute, 2–12–1, Hisakata, Tempaku-ku, Nagoya-shi 468–8511, Japan The absorption and emission spectra of Ni-doped glasses and transparent glass-ceramics are discussed in relation to its coordination number. The results evidenced that the color changed drastically to deep pink from yellow for the lithium metasilicate crystal based transparent glass-ceramics and to blue from brown for the spinel crystal based transparent glass-ceramics after crystallization, respectively. The absorption spectra of lithium metasili- cate and Spinel glasses suggest the existence of a tetrahedral Ni 2 ion and a trigonal bipyramid Ni 2 ion. On the contrary, tetrahedral Ni 2 ions in the lithium metasilicate transparent glass-ceramics and the octahedral Ni 2 ion in Spinel transparent glass-ceramics are dominant. The emission at around 580 nm was observed in Spinel trans- parent glass-ceramics under the excitation of 380 nm, however, a very weak or no emission was observed in the lithium metasilicate glass, lithium metasilicate transparent glass-ceramics and Spinel glass under the excitation of 430 nm. This emission might be due to a 1 T 1 D q 3 A 2 F transition after the excitation from 3 A 2 F to 3 T 1 P of the octahedral Ni 2 ions. In addition, only Spinel transparent glass-ceramics exhibits a broad NIR emission at around 1220 nm under the excitation of a 974 nm laser diode. This emission may be due to 3 T 2 F q 3 A 2 F tran- sition. It is considered that the tetrahedral Ni 2 ion is located between the chains in the lithium metasilicate crystal. =Received May 25, 2006; Accepted July 20, 2006? Key-words : Ni 2 ion, Transparent glass-ceramics, Absorption spectra, VIS–NIR emission spectra, Coordina- tion number 1. Introduction Ni-doped glasses tend to absorb over the entire visible spec- trum typically producing brown colored glasses, and it was concluded that Ni was present as Ni 2 in a wide range of com- positions in both four-=Ni4? and six-coordination=Ni6? with oxygen in the past. 1,2 Although the Ni 2 ion has a clear preference for octahedral coordination, it was well known that tetrahedral Ni 2 ion favorably appeared in high-alkali borate and borosilicate glasses and octahedral Ni 2 ion existed in low alkali borate and borosilicate glasses, and their color were pink and green-blue, respectively. 3,4 Their optical properties have been recognized using ligand field theory. 3 However, recently the modern spectroscopic techniques EXAFS etc. have confirmed that a trigonal bipyramid Ni 2 =Ni5? also presented in many glasses and the brown colored glasses con- tained both =Ni4? ion and Ni=5? 5–8 ion, and Ni was found with three coordination numbers 6, 5 and 4 in some glasses. 6 The color of glasses changes depending on the frac- tion of these Ni ions. The spectroscopy of the Ni 2 ion-doped single crystals and glass-ceramics has received much attention in recent years. Much of the present interest focuses on the possibility of Ni 2 - doed materials as active media for tunable near infrared lasers. 9–12 In these materials, Ni 2 ion occupies octahedral sites and exhibits a broad emission in near infrared region 1100–1600 nm. In contrast, no emission of tetrahedrally coordinated Ni 2 ion even at cryogenic temperature has been reported. In this paper the absorption and emission spectra of Ni- doped glasses and glass-ceramics are discussed in relation to its coordination number. 2. Experimental 2.1 Sample preparation The compositions of glasses studied are shown in Table 1. These glasses are able to convert to transparent glass-ceramics based on Li 2 OெSiO 2 crystal LS3 and Spinel crystal =Mg, Zn Al 2 O 4 ?Spinel by adequate heat treatment. High purity silica sand, alumina and reagent grade chemi- cals of Li 2 CO 3 ,K 2 CO 3 , MgO, ZnO, TiO 2 , ZrO 2 and NiO were used as raw materials. Batches corresponding to 50 g of glass were mixed thoroughly and melted in a 50 cc PtRh10 crucible under appropriate condition in an electric furnace in air. After melting they were poured onto iron plate and pressed by another iron plate. Then they were annealed at suitable condi- tions and cooled slowly in the furnace. The glasses were heat treated under various conditions for nucleation and crystallization. The glasses and glass-ceramics were cut and polished optically into about 1 mm in thickness for optical measurement. 2.2 XRD Crystalline phases, percent crystallinity and crystalline size were measured by powder X-ray diffraction analysis XRD, Bruker, AXS Model D5005 under the condition of Cu Ka radiation l0.154 nm, 40 kV-40 mA, 0.01c step and 1 s step. The percent crystallinity was determined using Ohlberg and Strickler's method. 13 a-Quartz crystal and parent glasses