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A new of 2D transition metal thiophosphates, Nb 4 P 2 S 21 , was synthesized through a vapor transport reaction. High purity and centimeter-scale large Nb 4 P 2 S 21 crystals were obtained by controlling the growth temperature and stoichiometric ratio between niobium, phosphorus, and sulfur (using excess sulfur condition, Nb: P: S = 4: 2: 23). It was confirmed that large Nb 4 P 2 S 21 crystals could be separated to a nanometer scale through mechanical exfoliation, and the exfoliated Nb 4 P 2 S 21 layer exhibits semiconducting characteristics by measuring the change in electrical conductivity with temperature (increased conductivity with temperature in the range of 93–333 K). Furthermore, the device characteristics for detecting visible ray laser (635 nm) and NO 2 gas molecules were verified. Based on these characteristics, the synthesized 2D material is expected to be a potential candidate for additional 2D materials and in multi-functional sensor devices, including optoelectronics and gas sensing applications. • Synthesis of 2D transition metal thiophosphates Nb 4 P 2 S 21. • Bulk to few nanometer scale separation of Nb 4 P 2 S 21 using mechanical exfoliation. • Multi-functional sensing application in photodetector and gas sensor. [ABSTRACT FROM AUTHOR]