STRUCTURAL AND OPTOELECTRONIC STUDIES OF Er3+/Yb3+ CO-DOPED SrBi2Nb2O9 FERROELECTRIC CERAMIC

Abstract

A series of SrBi2-x-yNb2ErxYbyO9 ferroelectric ceramics (x= 0.03, y= 0.01, 0.03,0.06, 0.09, and 0.12) has been prepared by the solid-state reaction method. The precursors SrCO3, Bi2O3, and Nb2O5 were used for undoped SrBi2Nb2O9 (SBN) while Er2O3, and Yb2O3 were used as dopants. Calcination of powder at 950⁰C for 3 hours and then pellets were sintered for 3 hours at 1050⁰C. The formation of pure phase SBN has been confirmed by XRD spectra corresponding to orthorhombic geometry having phase group A21am. The highest intensity plane was observed at (115) for all SBN compositions, conceding the bismuth layered structure with n = 2. Evaluation of lattice parameters from XRD shows the increase in orthorhombic distortion i.e., b/a value as the concentration of Yb3+ increases. The lattice parameters and unit cell volume increase as the content of Yb3+ rises. SEM study reveals the randomly oriented plate like structure of SBN. Their average particle sizes range from 1.12μm to 2.23μm to the concentrations x=0.03 and y=0.03. After a further rise in Yb3+ concentration, the average particle size decreases as the internal structure of the lattice is disrupted. The FTIR characteristic bands are found at wavenumber 540cm-1 , 602cm-1, and 812cm-1 . In PL spectra, two green emission bands (524nm and 549nm) and one weak red band (660 nm) are acquired using a 488nm excitation wavelength. The highest PL intensity is found at x=0.03, y=0.03 after this concentration the intensity degrades because of the concentration quenching effect. The excitation spectra are obtained at the emission wavelength of 549nm with maximum excitation obtained at 488nm. The UCL spectra excited by 980nm laser, show two UCL bands at 524nm and 549nm in the green region and a single red band at 660nm. The green band dominates for initial concentration up to x = 0.03, y = 0.03 after which red emission dominates as the concentration of Yb3+ increases. The findings suggest the tunability of green light into red light of Yb3+ doped Er3+ - SBN ferroelectric ceramic. Pump power analysis shows that the two photons contribute to green and red UC emissions. The time decay analysis of SBN composition showed that the average decay time of Er3+ is 70μs and that of Yb3+ is 37μs. The diffuse reflectance spectra revealed the band gaps of the ceramic samples ranging from values 2.7eV to 3.1eV.