This work unfolds the fundamental mechanisms and demonstrates the tunable optical properties derived via chemical composition tailoring in tungsten (W)-doped gallium oxide (Ga₂O₃) compounds. On the basis of the detailed investigation, the solubility limits of tungsten (W⁶⁺) ion and associated effects on the crystal structure, morphology, and optical properties of W-doped Ga₂O₃ (Ga_{2-2 x}W _xO₃, 0.00 ≤ x ≤ 0.25, GWO) compounds are reported. GWO materials were synthesized via a conventional solid-state reaction route, where a two-step calcination is adopted to produce materials with a high structural and chemical quality. X-ray diffraction analyses of sintered GWO compounds reveal the formation of a solid solution of GWO compounds at lower concentrations W ( x ≤ 0.10), while unreacted WO₃ secondary phase formation occurs at higher concentrations ( x>0.10). Insolubility of W at higher concentrations ( x ≥ 0.15) is attributed to the difference in formation enthalpies of respective oxides, i.e., Ga₂O₃ and WO₃. GWO compounds exhibit an interesting trend in morphology evolution as a function of W content. While intrinsic Ga₂O₃ exhibits rod-shaped morphology, W-doped Ga₂O₃ compounds exhibit nearly spherical-shaped grain morphology. Increasing W content ( x ≥ 0.10) induces morphology transformation from spherical to faceted grains with different facets (square and hexagonal). Relatively larger grain sizes in GWO compounds might be attributed to vacancy assisted enhanced mass transport due to W incorporation and/or WO₃ induced liquid phase sintering. Our findings demonstrate a substantial red shift in band gap ( E_g), which is evident from the optical absorption spectra, enabling the wide spectral selectivity of GWO compounds. W 5d orbitals induced sp- d exchange interaction between valence band and conduction band electrons accounts for the substantial red shift in E_g of GWO compounds. Also, with increasing W, E_g decreases linearly, obeying Vegard law up to x = 0.15 and, at this point, an abrupt E_g drop prevails. The nonlinearity ( bowing effect) behavior in E_g beyond x = 0.15 is due to insolubility of W at higher concentrations. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and band gap could be useful to optimize GWO materials for optical, optoelectronic, and photocatalytic device applications.

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