Optical properties of rare-earth doped epitaxial Sr_0.5Ba _0.5Nb₂O₆ thin films grown by pulsed laser deposition

Optical quality rare-earth (RE) (Nd³⁺, Eu³⁺, Gd ³⁺ and Yb³⁺) doped Sr_0.5Ba_0.5Nb ₂O₆ (SBN) epitaxial films of ∼ 170 nm thick have been successfully grown on MgO (100) single crystal substrates using pulsed laser deposition technique. Strong residual stress in these films has been revealed by Raman spectroscopic studies. Two kinds of in-plane orientations with respect to the MgO substrate co-exist. All the film samples show high transparency in the visible wavelength. Their band-gap energies appear to be independent of the types of dopant. Photoluminescence (PL) spectra of RE-doped SBN ceramics show a strong and broad emission band at around 600 nm (2.07 eV). The peak position of this emission band changes slightly with different RE-dopants. Thin film samples, however, yield a broad PL band at around 385 nm (3.22 eV). This UV emission shows no observable shift in the peak position for different dopants. Apart from these broad emission bands, conspicuous emission lines from Eu ³⁺ and Nd³⁺ ions are also noted. The origins of these PL spectra are discussed.