schemes that integrate the ZGO:Cr 3+ . The first, a traditional ionophore-based approach , couples the ZGO:Cr 3+ persistent luminescence to the variable absorption of a lipophilic pH indicator. By including a selective ionophore for K + , Na + , or Ca 2+ , the absorption/protonation of the indicator becomes dependent on the activity of the respective ion in the aqueous phase, and we demonstrate four different sensors based on the same architecture (Scheme 1A) . The second sensing scheme is a design for ratiometric, time-resolved O2 sensing by using the ZGO:Cr 3+ persistent luminescence as an internal standard signal to the O2 sensitive, phosphorescent emission of Palladium-TPTBP (Scheme 1B). For both systems, by using a time-resolved approach (Scheme 1C), we can exclude autofluorescence from biological samples and measure the sensor signal directly, even with significant spectral overlap. Scheme 1. Sensing Mechanisms a A) Ion-selective PLN mechanism: ions in the surrounding bulk phase displace a proton from the pH-sensitive blueberry dye, increasing its absorbance which gates the persistent luminescence of ZGO:Cr 3+ B) O2 PLN mechanism: a ratiometric readout where PdTPTBP is dynamically quenched by O2 while the ZGO:Cr 3+ is unaffected by O2. C) Approach for time-resolved luminescence detection with PLNs.