The preparation of room temperature phosphorescent carbon dots still faces great challenges, especially in the case of carbon dots endowed of visible-light excitable room temperature phosphorescence (RTP). To date, a limited number of substrates have been exploited to synthesize room temperature phosphorescent carbon dots, and most of them can emit RTP only in solid state. Here, the synthesis of a composite obtained from the calcination of green carbon dots (g-CDs) blended with aluminum hydroxide (Al(OH)3) is reported. The resultant hybrid material g-CDs@Al2O3 exhibits blue fluorescence and green RTP emissions in an on/off switch process at 365 nm. Notably, this composite manifests strong resistance to extreme acid and basic conditions up to 30 days of treatment. The dense structure of Al2O3 formed by calcination contributes to the phosphorescent emission of g-CDs. Surprisingly, g-CDs@Al2O3 can also emit yellow RTP under irradiation with white light. The multicolor emissions can be employed for anti-counterfeiting and information encryption. This work provides a straightforward approach to produce room temperature phosphorescent carbon dots for a wide range of applications