May 2010, Volume 4, No.5 (Serial No.30) Journal of Chemistry and Chemical Engineering, ISSN 1934-7375, USA Optical Absorption and Refractive Index Study of Ti: Al 2 O 3 Single Crystal Hamdan Hadi Kusuma 1,2 , Zuhairi Ibrahim 1 and Mohamad Khairi Saidin 1 1. Physics Department, Faculty of Science, Universiti Teknologi Malaysia, UTM Skudai Johor 81310, Malaysia 2. Physics Education Department, Faculty of Mathematic and Natural Science Education, IKIP PGRI Semarang 50125, Indonesia Received: March 30, 2010 / Accepted: April 12, 2010 / Published: May 30, 2010. Abstract: The optical absorption of Ti:Al 2 O 3 single crystal has been measured at room temperature, in the wavelength region between 200 nm and 800 nm. The main absorption peaks at 491 nm and 562 nm, the weak infrared absorption band with a peak at 650 nm and the strong UV absorption band below 300 nm were observed. The refractive index is discussed by using Fresnel’s equation. In particular, the Sellmeier equation was determined in the visible region by means on non-conventional method based on the measurement of refraction by using UV-visible spectroscopy. The refractive indices decreased from 3.71 to 1.28 with wavelength in the range 400 - 800 nm. Key words: Optical absorption, refractive index, Ti: Al 2 O 3 , UV-visible spectroscopy. 1. Introduction Aluminum oxide (Al 2 O 3 ) is a technological and industrial material of great interest, both for fundamental studies and for application, because of its hardness, good electrical insulation, useful optical properties, high surface area, and catalytic surface activity [1]. Aluminum oxide (sapphire), an important technological material, is used as lasing material in solid state lasers, substrate for micro-electronics ceramic, radiation dosimeter, an insulator for the wall of nuclear fusion reactors and so on [2]. Pure Al 2 O 3 is a durable material with optical transmission spanning the range from UV to IR. Discovery of lasing action in Cr doped Al 2 O 3 has created a basis of modern laser technologies. This role has been taken over more recently by Al 2 O 3 doped Ti that is now successfully used as tunable laser material [3]. Ti: Al 2 O 3 (Ti: sapphire) is useful tunable laser material in the near infrared spectra region of 0.7 nm - 1.1 μm. Crystal of Corresponding author: Hamdan Hadi Kusuma, PhD Student, research field: materials science. E-mail: coesma@yahoo.com. Ti: Al 2 O 3 exhibits a broad absorption band, located in the blue-green region of the visible spectrum that is associated with phonon-coupled excitation of the 3d electron of the Ti 3+ ions [4]. Optical properties of Ti: Al 2 O 3 crystals have been studied [3-7]. The measurement of the optical absorption coefficient near the fundamental absorption edge is a standard method for the investigation of optically induced electronic transition in many materials. Generally, two types of optical transition, i.e. direct and indirect, occur at the absorption edge [8]. Both of these transitions occur when an electromagnetic wave interacts with a valence electron and raises it across the energy gap to the conduction band. In this paper, a detailed investigation on the optical absorption of Ti: Al 2 O 3 in the visible and UV region is presented. The room temperature reflectance and transmittance data is analyzed to identity the refractive index of the single crystal Ti: Al 2 O 3 . The refractive index of a material depended on the crystal structure