<p>Real-time, online and accurate detection of ferric/ferrous ions is quite important for environmental protection and healthcare, which is preferred by portable fluorescent sensors (in solid state) compared to previous sensors (dominant in liquid or turbid suspensions) associated with susceptibility to oxidation and precipitation. Considering the scarcity of the solid-state fluorescent sensors, a nitrogen-doped carbon quantum dots (NCQDs) encapsulated ZIF-8 (NCQD@ZIF-8) photonic crystal (PC) sensor for Fe³⁺ and ascorbic acid detection in solid state was constructed by rapid evaporation self-assembly technique. The fluorescence intensity of NCQD was enhanced with slow light effect of ZIF-8 PC. Fe³⁺ was selectively detected based on its ability to quench the fluorescence of QDs@ZIF-8 PC through a combination of the internal filter effect and possible Fe³⁺−QDs complexation. Detection of ascorbic acid (AA) was based on the fact that AA can recover the fluorescence intensity of the NCQD@ZIF-8 PC quenched by Fe³⁺ due to AA reduction of Fe³⁺ to Fe²⁺. Both Fe³⁺ and ascorbic acid can be quickly and selectively detected by the NCQD@ZIF-8 PC sensor in the linear range of 0. 1− 10 mmol L^− 1 (R²= 0.996) with detection limits of 0.06 mmol·L^− 1 and 100 µL sample consumption. Iron speciation analysis (Fe³⁺ and Fe²⁺) in simulated water samples was realized with good precision and accuracy. The NCQD@ZIF-8 PC sensor provided a rapid and portable way for determination of Fe²⁺/Fe³⁺ in environmental samples and new possibilities for device fabrication.</p> Graphical Abstract <p></p>