Ag/Ag–Cu doped ZnO/graphene coated with STMS/SDTMS for UV detection: Theoretical and experimental studies

The impact of Ag and Ag–Cu codoping on the structure and optical performance of ZnO composite graphene (ZnO/G) was investigated. Moreover, the photoelectric properties of G, ZnO, and Ag–Cu co-doped ZnO/G (different numbers of doped atoms) were analyzed based on first-principles calculations. ZnO/G, Ag-doped ZnO/G (1%–4%), and Ag–Cu co-doped ZnO/G (1%–4%) were prepared using the hydrothermal method. Energy-dispersive X-ray spectroscopy and scanning electron microscopy were performed to characterize their structures and morphology. Single-mode–tapered-multimode–single-mode (STMS) and single-mode–double-tapered-multimode–single-mode (SDTMS) sensor units were designed based on evanescent field theory. RSOFT simulated their structural properties and then experimentally validated them. The prepared materials were coated with STMS and SDTMS sensor units for UV detection experiments. When 1% Ag–Cu co-doped ZnO/G was coated with SDTMS, the highest sensitivity obtained was − 1.367 × 10−1 mW/mW·cm−2. Ag–Cu codoping affected the free-carrier concentration of the ZnO composite under UV illumination, which altered the refractive index of the materials and resulted in a change in the transmission spectrum of the sensor. The results show that the Ag–Cu co-doped ZnO modification coated with SDTMS can effectively improve the UV light–absorption properties of the sensors. This method will play a significant role in future applications of UV detection.