Optical properties of neodymium doped lithium niobate single crystals grown by czochralski method

Abstract

LiNbO3 and Nd3+ doped LiNbO3 crystals have successfully been grown by using Czochralski (CZ) method. Their crystallinity has been confirmed using X-ray diffraction (XRD) technique and the result has been used to determine the lattice parameters. The density of the crystals is measured using Archimedes principle while the transmission spectra are obtained using Fourier Transform Infrared Spectroscopy (FTIR). Their absorption characteristic is determined using Ultra Violet-Visible (UV-Vis) Spectroscopy. From the X-ray diffraction spectra, it is found that the samples exhibit single phase congruent composition and the lattice parameter of a and c are in the range of 5.1423Å – 5.1711Å and 13.8482Å – 13.9258Å, respectively. The crystals density is found to be ranging from 4.637 g cm-3 – 4.649 g cm-3 and it is in the increasing trend with respect to Nd3+ content. The crystals present a broad OH- absorption band located at approximately 3486 cm-1. It is observed that the addition small amount of Nd3+ ion into the system has small effect on the absorption band position and does not change the crystal structure. It is also found that the increasing amount of Nd3+ content caused the optical band gap Eg to increase from 3.72 eV to 3.80 eV and 3.48 eV to 3.60 eV for direct transition allowed and forbidden, respectively. Meanwhile, the Eg for indirect transition allowed and forbidden are about 3.36 eV – 3.52 eV and 3.15 eV – 3.36 eV, respectively. The Urbach energy, ∆E is found to be in the range of 0.30 eV – 0.45 eV and increases with Nd3+ content. Meanwhile, the addition of Nd3+ ion caused the refractive index to decrease from 2.480 to 2.008 and increase the Judd-Ofelt intensity parameters, from 0.3006×10-19 to 1.8490×10-19 for Ω2, 0.9213×10-19 to 4.4042×10-19 for Ω4 and 0.9511×10-19 to 6.2420×10-19 for Ω6.