APTES Modified GO-PEI-Er3+/Yb3+: NaYF4 Upconverting Nanoparticles Hybrid Film-Based Optical Ph Sensor and NIR Photoelectric Response

The film containing polyethyleneamine (PEI), aminopropyltriethoxysilane (APTES), Er3+/Yb3+:NaYF4 nanoparticles (NPs), and graphene oxide has been developed. The developed films have been structurally and optically characterized. The upconversion (UC) emission-based pH dependent study to sense the pH upon excitation at 980 nm diode laser radiation has been performed. The UC emission intensity is significantly reduced for pH similar to 9 and explained due to the strong interaction between graphene oxide and PEI-APTES-Er3+/Yb3+:NaYF4 UC NPs. The developed film is also found more sensitive to the urine as observed from the UC emission measurement, exhibiting good repeatability and high stability. The UC emission intensity for both the green and red hands arising from the Er3+ ion in the developed film shows a decreasing trend with the increase in pH values (pH range of 5-9). The photocurrent response of the developed films (i.e., film 2 and film 3) coated on FTO glass plate upon excitation at 980 nm laser radiation shows the increment in the current values by similar to 17% and similar to 14%, respectively, when the pump power density of the excitation source reaches to 1.5 W/mm(2).