Optical, luminescence and magnetic properties of braunite‒rhodonite nanocomposites synthesized by green aqueous sol‒gel route

Braunite (Mn₇SiO₁₂)‒rhodonite (MnSiO₃) nanocomposites have been synthesized utilizing a green aqueous citrate sol‒gel route. The influence of heat-treatment temperature on the structure and properties of these nanocomposites was investigated. X-ray diffraction and high resolution transmission electron microscopy analyses demonstrated that well-crystallized nanoparticles, having average sizes in the range of 18‒42 nm, were produced. MnSiO₃-content increased in the nanocomposites with increasing calcination temperature from 600 to 900 °C. Optical, photoluminescence and magnetic properties were determined. Ultraviolet-visible-near infrared diffuse reflectance spectra were used, applying Kubelka-Munk function, for optical absorbance calculation and determination of the band gap energy (E_g). Optical absorption spectra exhibited bands at 415‒438 nm originated from Mn²⁺ ions, and other bands at 550 and 599 nm due to absorption of Mn³⁺ ions. E_g was found to increase with increasing MnSiO₃-content in the nanocomposites. The obtained nanocomposites gave green fluorescence emissions at 525‒565 nm, a yellow emission at 584 nm and red emissions at 619 nm. All the synthesized nanocomposites exhibited antiferromagnetic properties in which the paramagnetic contribution and magnetization increased as the MnSiO₃-content increased. The present nanocomposites are promising candidates for application as light emitting diodes as well as magnetoelectronic materials which are used in biomedical applications.