Appl Phys B (2009) 96: 433–437 DOI 10.1007/s00340-009-3588-7 Linear and nonlinear optical properties of rare earth doped of Ba 0.7 Sr 0.3 TiO 3 thin films R. Reshmi · R. Sreeja · M.K. Jayaraj · J. James · M.T. Sebastian Received: 20 October 2008 / Revised version: 8 May 2009 / Published online: 5 June 2009 © Springer-Verlag 2009 Abstract Ba 0.7 Sr 0.3 TiO 3 :Eu ferroelectric films were de- posited on quartz substrates by pulsed laser deposition. The linear absorption coefficient and the linear refractive index calculated from the transmission spectrum at 532 nm were found to be 1.67 × 10 4 cm −1 and 1.82 respectively. The room temperature photoluminescence shows the character- istic emission of Eu 3+ ions. The nonlinear optical properties of the film were investigated by a single beam Z-scan setup. The negative nonlinear refractive index and two photon ab- sorption coefficient was found to be −1.508 × 10 −6 m 2 /GW and 240 m/GW respectively. The real and imaginary part of the third order susceptibility of the thin films is 2.58 × 10 −17 m 2 /V 2 and 1.16 × 10 −16 m 2 /V 2 respectively. The BST:Eu thin films show good optical limiting property. PACS 42.70.Mp · 77.84.-s · 85.60-q 1 Introduction Thin films of Ba 0.7 Sr 0.3 TiO 3 have been intensively stud- ied for application in high density dynamic random ac- cess memories (DRAMs), monolithic microwave integrated circuit used for capacitors, tunable microwave filters and phased array antennas [1–3]. R. Reshmi · R. Sreeja · M.K. Jayaraj ( ) Optoelectronic Devices laboratory, Department of Physics, Cochin University of Science and Technology, Kochi 682022, India e-mail: mkj@cusat.ac.in J. James · M.T. Sebastian National Institute of Interdisciplinary Science and Technology, Thiruvananthapuram 695019, India Materials exhibiting nonlinear properties are of much in- terest, in particular those exhibiting strong nonlinear opti- cal absorption as an optical limiting material. Optical lim- iting materials find potential application for the protection of eyes and optical sensors against damage on exposure to sudden intense light, since they provide a very fast response and generally show relatively high linear transmission. The mechanism producing nonlinear absorption is the reverse saturable absorption (RSA) or excited state absorption or two photon absorption [4]. Ba (1−x) Sr x TiO 3 (BST) thin films exhibit large micro- wave tunability up to 23.7 GHz [3]. This feature had mo- tivated the study of nonlinear dielectric properties of these materials in the optical frequency region. The electro-optic (EO) characterizations of BST films reveal an EO coeffi- cient with a very large saturation value of the field-induced birefringence at the wavelength of 632.8 nm [5]. Opti- cal second-harmonic generation (SHG) has also been ob- served in the NIR (near infra-red) wavelength of 1.06 μm [6] using a Q-switched Nd-YAG laser and at 760 nm using mode-locked Ti:Sapphire laser [7, 8]. A thin film of BST shows nonlinear optical absorption and refraction and hence is a good candidate for nonlinear application. The non- linear optical absorption and refraction of the polycrys- talline Ba 0.7 Sr 0.3 TiO 3 film on quartz substrate have been reported as 1.2 × 10 −6 m/W and 1.08 × 10 −15 m 2 /V 2 , re- spectively [9]. But the nonlinear absorption and refraction coefficients of epitaxial Ba 0.6 Sr 0.4 TiO 3 thin films grown on MgO are much lower [10]. The large values of the nonlin- ear optical absorption and refraction observed for the BST polycrystalline film have been attributed to the small grain size and good homogeneity [9]. Rare earth (RE) ions exhibit a characteristic intra 4f shell luminescence which is almost insensitive to host material