<p>As a type of potential material with room-temperature phosphorescence, carbon dots usually need to be embedded in heterogeneous matrix such as boronic acid, polyvinyl alcohol, and melamine to effectively suppress the non-radiative transitions of triplet excitons and ultimately achieve room-temperature phosphorescence. An intriguing question is whether embedding carbon dots into a homogeneous matrix, rather than a heterogeneous one, could facilitate room-temperature phosphorescence. In this paper, we reported carbon dots@homogenous matrix composite with room-temperature phosphorescence via a controllable carbonization technology using <i>o</i>-phenylenediamine as the sole precursor. Our results demonstrate that amorphous polymer dots (PDs) are generated via the polymerization of <i>o</i>-phenylenediamine. Subsequently, a portion of the PDs undergoes further carbonization, forming crystalline carbonized polymer dots (CPDs) under controlled trace amounts of acid. As a result, carbon dots@homogenous matrix (marked by CPDs@PDs) composite formed <i>in situ</i>. Due to the homology between CPDs and PDs, CPDs have strong π-π interactions with PDs homogenous matrix, which seriously affects the emission of CPDs. On one hand, the strong π-π interactions result in the quenching of the fluorescence emission peak of CPDs at 595 nm, while the fluorescence emission band of CPDs in the range of 430 to 530 nm is retained. On the other hand, the strong π-π interactions effectively inhibit the non-radiative transitions of the triplet exciton, ultimately leading to room-temperature phosphorescence. In comparison, CPDs embedded in the heterogeneous matrix have no room-temperature phosphorescence. In this sense, a homogeneous matrix based on the strong π-π interactions provides another way to achieve room-temperature phosphorescence besides the traditional way of heterogeneous matrices based on hydrogen bonds or covalent bonds.</p>