This article describes the synthesis of ZnO nano particle with an average crystallite size ~20 nm through aqueous solution growth technique using Benzyltrimethylammoium hydroxide Ionic liquid (BTMAH) as a structure directing agent. Crystallinity, phase purity, Volume of unit cell, average crystallite size, and strain were confirmed by X-ray diffraction pattern using Scherrer‟s method and Williamson-Hall analysis, particle morphology and grain size were confirmed by Atomic force microscopy. Using the optical properties photo luminescence, interaction between ammonia gas and zinc oxide nanoparticle were also investigated. The material shows average significant increment in the PL intensity which conform its tremendous applicability in optical gas sensor to detect ammonia gas (25 ppm).