Influence of Molar Ratio and Lattice Strain on the Electronic Bandgap of Bismuth Chromium Oxide Nano particles

Bi2Cr4O15 nanoparticles doped with Eu3+, Tb3+, Dy3+, and Sm3+ were synthesized through a rapid combustion route, producing fine powders with nanoscale crystallinity. X-ray diffraction confirmed the formation of a single-phase chromite structure, while minor peak broadening and shifts indicated lattice distortion arising from the incorporation of rare-earth ions. The combustion process generated irregular, agglomerated particles, typical of reactions involving rapid gas release. The optical response of the doped samples shows a clear dependence on dopant species and concentration. Eu3+ and Sm3+ incorporation resulted in a gradual increase in the optical band gap (Eg) with higher mol%, suggesting modification of the electronic states and strengthening of local crystal field interactions. Tb3+ doping exhibited a steady decrease in Eg, whereas Dy3+ demonstrated a linear band-gap enhancement across the studied range. The relationship between lattice strain and Eg further highlights the structural influence of RE doping. Eu3+ and Sm3+ doped samples showed increasing strain with higher Eg, while Tb3+ doped nanoparticles displayed reduced strain as the band gap narrowed. Dy3+ doping produced a nonlinear strain profile, indicating more complex local rearrangements. Overall, the study demonstrates that selective rare-earth doping offers an effective route to tune the electronic structure and strain state of bismuth chromite, enabling tailored optical properties for functional applications.