Detection of sulfide ions in the red-light region based on upconverting NaYF4:Yb,Er/NaGdF4 core–shell nanoparticles

Long wavelength luminescent NaYF4:Yb,Er/NaGdF4 core–shell upconversion nanoparticles that were synthesized and modified with poly(acrylic acid) (PAA) were used to detect sulfide ions. The NaYF4:Yb,Er/NaGdF4 core–shell upconversion nanoparticles were synthesized to give an emission peak in the red-light region. When the carboxyl-functionalized NaYF4:Yb,Er/NaGdF4 core–shell upconversion nanoparticles and cupric ions (Cu2+) were mixed, the luminescence was quenched because of coordination between the carboxyl of PAA and Cu2+. However, when sulfide ions were added into the system, due to the competitive binding between S2− and Cu2+, the luminescence of the NaYF4:Yb,Er/NaGdF4 core–shell upconversion nanoparticles was recovered. Based on the recovery of the luminescence intensity, a turn-on system for the detection of sulfide ions was designed. Under optimal conditions, the linear range for the detection of sulfide ions ranged from 2.63 × 10−2 to 2.25 × 102 μM (R = 0.99) with a limit of detection for sulfide ions as low as 2.20 × 10−2 μM. The method was successfully applied to sulfide ion sensing in different environments.