Al-mediated doping boosts photocatalysis and room-temperature ferromagnetism in Sol-Gel ZnS thin films

Aluminum-doped zinc sulfide (Zn₁₋ₓAlₓS, 0 ≤ x ≤ 0.05) thin films were fabricated using a sol–gel dip-coating technique to systematically investigate the relationship between Al dopant concentration, photocatalytic performance, and magnetic behavior. Comprehensive structural, optical, electrical, and magnetic characterizations indicate that moderate Al-doping provides an optimal balance between band-structure modulation and defect-state formation in ZnS. X-ray diffraction analysis confirmed the formation of phase-pure cubic ZnS with enhanced crystallinity, while SEM and XPS results supported a homogeneous distribution of Al dopants without detectable secondary phases. UV–Vis absorption spectroscopy combined with Tauc plot analysis demonstrated a gradual bandgap reduction from 3.60 to 3.42 eV, accompanied by an increase in sub-band-gap absorption. Photoluminescence quenching, together with Hall effect measurements, indicated suppressed radiative recombination and increased carrier concentration, which correlates with the enhanced photocatalytic degradation efficiency of methylene blue (99.5% after 150 min under UV irradiation). Moreover, Al substitution was found to induce a transition from paramagnetic to robust room-temperature ferromagnetic behavior, which can be attributed to defect-mediated exchange interactions and Anderson-type super-exchange mechanisms between donor electrons and S²⁻ p-states. The coexistence of tunable optical properties, enhanced photocatalytic activity, and room-temperature ferromagnetism suggests that moderately Al-doped ZnS thin films are promising candidates for multifunctional optoelectronic, spintronic, and environmental remediation applications.