Defect-Driven Optical Modulation in Rare-Earth-Modified Zn₂SnO₄ Spinels for Advanced Optoelectronic Applications

Spinel-type Zn₂SnO₄ and its La- and Ce-modified variants were synthesized via a solid-state route to investigate aliovalent substitution-induced structural, optical, and photoluminescence (PL) modulation. Undoped, La- and Ce-doped Zn₂SnO₄ samples were characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, ultraviolet-visible spectroscopy, photoluminescence, scanning electron microscopy (SEM)-energy-dispersed spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. XRD confirmed the dominant cubic spinel structure (Fd3̅m:1) with a minor SnO₂ phase, while rare-earth incorporation induced lattice expansion, microstrain, and reduced crystallite size (32-27 nm). FTIR, Raman, and XPS analyses revealed dopant-induced lattice distortion, enhanced oxygen-vacancy-related defects, and the presence of Zn²⁺, Sn⁴⁺, La³⁺, and mixed Ce³⁺/Ce⁴⁺ states. Optical studies showed band gap narrowing from 3.57 eV (undoped) to 3.16 eV (La-doped) and 3.12 eV (Ce-doped), extending visible-light activity. PL results demonstrated dopant-selective color tunability, with orange emission for La-doped and green emission for Ce-doped Zn₂SnO₄. These findings establish a clear structure-defect-optical correlation and highlight rare-earth-modified Zn₂SnO₄ as a promising material for visible-light optoelectronic, luminescence, and optical sensing applications.