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Mi-Yang Kim and Wha-Tek Kim Department of Physics, Chonnam National University, and Kwangju Branch, Korea Basic Science Institute, Kwangju 500-757, Republic of Korea

Moon-Seog Jina) Department of Physics, Dongshin University, Naju 520-714, Republic of Korea

Sung-Hyu Choe Department of Physics, Chosun University, Kwangju 501-759, Republic of Korea

Tae-Young Park Department of Physics, Wonkwang University, Iri 570-749, Republic of Korea

Kwang-Ho Park and Duck-Tae Kim Department of Electronics, Dong-A Junior College, Youngam 526-870, Republic of Korea (Received 2 April 2002; accepted 3 June 2002)

BaIn2S4, BaIn2S4:Ho3+, BaIn2S4:Er3+, BaIn2S4:Tm3+, BaIn2Se4, BaIn2Se4:Ho3+, BaIn2Se4:Er3+, and BaIn2Se4:Tm3+ single crystals were grown by the chemical transport reaction method. The optical energy gap of the single crystals was found to be 3.057, 2.987, 2.967, 2.907, 2.625, 2.545, 2.515, and 2.415 eV, respectively, at 11 K. The temperature dependence of the optical energy gap was well fitted by the Varshni equation. Broad emission peaks were observed in the photoluminescence spectra of the single crystals. They were assigned to donor–acceptor pair recombination. Sharp emission peaks were observed in the doped single crystals. They were attributed to be due to radiation recombination between the Stark levels of the Ho3+, Er3+, and Tm3+ ions sited in C1 symmetry.

I. INTRODUCTION

BaIn2S4and BaIn2Se4 compounds with an orthorhombic structure1,2 are wide-gap semiconductors with optical energy gaps of 3.057 and 2.62 eV,3 respectively. They have been expected to be useful materials applicable to optoelectronic devices in the violet-to-visible wavelength region. Nevertheless, except for their crystal structures, body color, and photoluminescence (PL) properties,1,4 no study has been reported as yet because it is difficult to grow single crystals, and they are destroyed by absorbing moisture in the atmosphere. Rare-earth element-doped BaIn2S4 and BaIn2Se4 single crystals have not been studied at all. This study investigated optical properties of undoped and Ho3+-, Er3+-, and Tm3+-doped BaIn2S4 and BaIn2Se4 single crystals. Undoped and Ho3+-, Er3+-, and Tm3+doped BaIn2S4 and BaIn2Se4 single crystals were grown by using the chemical transport reaction (CTR) method.

a)

e-mail: [email protected] J. Mater. Res., Vol. 17, No. 8, Aug 2002

http://journals.cambridge.org

Downloaded: 29 Mar 2015

The crystal structure of the single crystals was investigated by measuring their powder x-ray diffraction patterns. The optical absorption near the fundamental absorption edge and the PL spectra of the single crystals were measured. The optical energy gap of the single crystals was obtained. The temperature dependence of the optical energy gap and the transition mechanism of the emission peaks were investigated.

II. EXPERIMENTAL PROCEDURE A. Crystal growth of undoped and Ho3+-, Er3+-, and Tm3+-doped BaIn2S4 and BaIn2Se4 single crystals

BaIn2S4, BaIn2S4:Ho3+, BaIn2S4:Er3+, BaIn2S4:Tm3+, BaIn 2 Se 4 , BaIn 2 Se 4 :Ho 3 + , BaIn 2 Se