Synthesis, Characterization, and Optical Properties of Undoped and Te‐Doped W(S _<i>x</i> Se _{(1− <i>x</i> )} ) ₂ and Core‐Shell WS ₂ @W(S _<i>x</i> Se _{(1− <i>x</i> )} ) <sub>2</sub

WS 2 nanotubes (NTs) are layered transition‐metal dichalcogenides whose diameter strongly influences strain and optical properties. Alloying sulfur with selenium in W(S x Se 1− x ) 2 NTs provides compositional tunability, yet the link between precursor composition, alloy formation, and optical response remains unclear. In this work, W(S x Se 1− x ) 2 (WSSe) NTs with controlled S/Se ratios were synthesized and characterized using Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, STEM‐EDS, and X‐ray diffraction. The synthesis produced high yields of small‐diameter NTs (&lt;30 nm). Compositional analysis revealed sulfur enrichment relative to the nominal precursor ratio, while the interlayer spacing increased from 0.62 to 0.66 nm with increasing selenium content. To examine incorporation of heavier chalcogens, tellurium (Te) was introduced during synthesis. Owing to its larger atomic radius and lower chemical reactivity compared with sulfur and selenium, Te incorporation presents a significant kinetic limitation during NT growth. Elemental analysis shows that Te is incorporated only at trace dopant levels (&lt;1 at%) rather than forming a quaternary alloy phase. Despite this low incorporation, Te doping induces a measurable red shift of the A‐exciton transition, indicating a slight reduction in bandgap energy. Core–shell WS 2 @WSSe NTs were also synthesized, exhibiting nonlinear optical effects. These findings may enable alloyed TMD NTs for nanoscale optoelectronic and photodetection devices.