Role of Ba in engineering band gap, photoluminescence and nonlinear optical properties of SnO₂ nanostructures for photovoltaic and photocatalytic applications

In this article, we present the role of Ba doping in tuning energy gap, photoluminescence (PL) and third-order optical nonlinearity χ⁽³⁾ of SnO₂ nanostructures. Surface morphology analysis indicates the fragmentation of larger grains upon Ba incorporation possibly caused by the lattice mismatch effects. X-ray diffraction reveals polycrystalline nature of the nanostructures with rutile tetragonal structure. A shift in preferential growth orientation plane (200, 211, 110) has been observed with increase in Ba concentration. PL spectroscopy studies confirms the crystallinity of the films ruling out the presence of Sn interstitials. The green luminescent center at 550 nm and trap emission at 578 nm are attributed to singly ionized charge state of the oxygen and defect levels in band gap. Relatively large change in the band gap (3.64 eV −3.13 eV) arises due to Ba doping points the credibility of SnO₂ thin films for use in photovoltaic and photocatalytic applications. Third-optical nonlinearity of the films investigated by Z-scan technique shows χ⁽³⁾ as high as 3.37 × 10⁻³ esu indicating the suitability of SnO₂ nanostructures in nonlinear optical (NLO) devices such as optical power limiters and switches.