Structural, diffuse reflectance and luminescence study of t-Mg${}_2$B${}_2$O${}_5$ nanostructures

We report here the structural, reflectance, photoluminescence and thermoluminescence study of t-Mg${}_2$B${}_2$O${}_5$ nanostructures synthesized using optimized combustion method relatively at much lower temperature. The rietveld refinement of X-ray diffraction data confirms single-phase triclinic crystal structure of Mg${}_2$B${}_2$O${}_5$ nanoparticles. The direct band gap determined using diffuse reflectance spectra (DRS) was 5.23 eV, which is contrary to earlier reports quoting Mg${}_2$B${}_2$O${}_5$ as indirect band gap material. To elucidate the nature of band gap in Mg${}_2$B${}_2$O${}_5$, we performed first principle calculations based on full potential linearized augmented plane-wave (FPLAPW) method, predicting the direct band gap of 5.10 eV in t-Mg${}_2$B${}_2$O${}_5$ which is in good agreement with our experimental results. The t-Mg${}_2$B${}_2$O${}_5$ nanoparticles were found to exhibit yellow-reddish photoluminescence peaking at 588 nm, attributed to various defects states. The combustion synthesized Mg${}_2$B${}_2$O${}_5$ nanocrystals exhibited ultraviolet (254 nm) responsive thermoluminescence (TL). TL glow curve of Mg${}_2$B${}_2$O${}_5$ comprises of one dominant peak around 417-428 K and less intense shoulder around 573-589 K which arouse possibility of various trapping sites or defects present in the sample. The TL analysis using general order Kitti's equations was performed to estimate the activation energies of trapping states. Owing to already well-known mechanical and thermal properties, the direct wide band gap nature and UV responsive thermoluminescence of combustion synthesized t-Mg${}_2$B${}_2$O${}_5$ nanostructures can pave way for its use in luminescence-based applications and UV dosimetry. As an additional application of Mg${}_2$B${}_2$O${}_5$, anti-biofilms activity of Mg${}_2$B${}_2$O${}_5$ nanoparticles using pseudomonas aeruginosa bacterial cells was also performed which revealed 91 ± 2.7% inhibition of biofilms formed by P. aeruginosa, respectively, at 100 µg/ml after 24 h of treatment.