Regulating novel tunable green to red upconversion luminescence in Er3+/Yb3+ co-doped SrBi2Nb2O9 ferroelectric ceramic

A series of SrBi_2-x-yNb₂Er_xYb_yO₉ (SBN) ferroelectric ceramics co-doped with Erbium and Ytterbium have been fabricated through solid-state approach, the formation of pure phase SrBi₂Nb₂O₉ has been confirmed by XRD spectra corresponding to orthorhombic geometry having phase group A21am. The lattice parameters and volume of the unit cell increase with the content of Yb³⁺. SEM study revealed the randomly oriented plate-like structure of SBN having average particle sizes ranging from 0.9 μm to 2.23 μm. The FTIR characteristic bands are found at wavenumber 602 cm⁻¹ and 812 cm⁻¹. In Photoluminescence (PL) spectra, two green emission bands (524 nm and 549 nm) and one weak red band (660 nm) are acquired using a 488 nm excitation wavelength. The diffuse reflectance spectra (DRS) of ceramic compounds reveal that the values of band gap ranges from values 2.7–3.1eV. Two UCL bands are seen at wavelength 533 nm, and at wavelength 554 nm in the green part of the upconversion photoluminescence (UCL) spectra, and a single band observed at a wavelength of 672 nm in the red region upon excited by 980 nm laser. The green band dominates for initial concentration up to x = 0.03, y = 0.03 after which red emission dominates with increasing concentration of Yb³⁺. The dependence study of pump power on UCL emission intensity reveals that there are two photons are involved in UC emissions of green and red. The time decay analysis of SBN composition showed that the average decay time of Er³⁺ is 70μs and that of the co-doped system (Er³⁺/Yb³⁺) is 37 μs