Lithium niobosilicate glass doped with samarium: Dielectric and optical analysis

Abstract

Lithium niobate (LiNbO3 - LN) is a large bandgap [3.78 eV at room temperature (RT)] semiconductor mainly known by its ferroelectric behaviour and excellent non-linear optical, electro-optical and piezoelectric properties. In this study 91SiO2-4Li2O-4Nb2O 5-1Sm2O3 (mol%) glasses were prepared by sol-gel. Glass-ceramics were obtained through heat-treatments (HTs) of the dried gel. The samples structure was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The HT above 600°C promotes the crystallization of LiNbO3 and SmNbO4. For heat HT above 800°C, SiO2 crystallites also precipitate. SEM micrographs indicate that the size of the particles and aggregation phenomena is promoted with the increase of the HT temperature. The electric characterization was performed as a function of the temperature and frequency. The main contribution for the electric conductivity behaviour is the number of network modifier ions, which decreases with the increase of the HT temperature. The dielectric constant and loss value decrease with the increase of the HT temperature. Dielectric relaxation mechanisms were observed in the samples HT below 800°C. At RT, the photoluminescence (PL) spectra, revealed a red light emission, due to the 4G5/2 a 6HJ = 5/2,7/2,9/2 transitions of Sm3+ ion. The results suggest that the intraionic emission is promoted when the lanthanide ions are inserted in the amorphous matrix. Auto-absorptions of the samarium ion and large emission bands were detected and assigned to the crystalline and amorphous phases of SiO 2. The obtained results reflect the decisive effect of HT temperature in the structural, electric and optical properties of these glasses. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.