The detection of oxygen (O-2) by optical sensors is of growing importance, for example, in biology, life science, environmental science, and aerodynamics, where the composition of gases is crucial for many applications. Purely organic optical O-2 sensors are very attractive for monitoring food deterioration, biosensing, and biomonitoring, as they can provide continuous, reversible, and nondestructive O-2 sensing. However, purely organic optical reversible O-2 sensors that can work with a broad O-2 concentration range and that have robust reversibility are yet to be realized. We hereby developed a purely organic optical O-2 sensor by embedding polyimide-based photoemitters within a poly(vinyl alcohol) (PVA) matrix. The photoemitters are synthesized through one-pot hydrothermal reactions. They have a lifetime of room temperature phosphorescence (RTP) of up to a few microseconds (mu s) when they are embedded into the polymer matrix. Our results demonstrate that the photoemitters have higher sensitivity and broader sensing range to O-2 if they are synthesized with longer reaction times because they possess a more rigid polyimide structure. The O-2 sensor with such optimized photoemitters embedded in the polymer matrix exhibits continuous and broad-range O-2 sensing in the range of 0-16% O-2. The Stern-Volmer quenching constant (Ksv) was calculated to be 0.2351 kPa(-1) for the linear response range of 0-4% O-2. Moreover, the O-2 sensor can be repetitively used at least 10 times in the linear range (04% O-2) or beyond the linear range (up to 21% O-2). The metal-free, purely organic sensors that enable the continuous and repetitive detection of O-2 within a relevant O-2 sensing range are appealing especially for monitoring packaged food, biomonitoring, and biosensing.