Fabrication of Y2O3:Bi3+,Eu3+ Fluorescent Nanosheet Films By Electrophoretic Deposition

Abstract

Spectral down-shifters convert near-UV light, to which silicon solar cells typically have low sensitivity, to visible light that solar cells can convert to electric power. They can therefore improve the photoelectric conversion efficiency of the solar cells. Y2O3:Bi3+,Eu3+ nanosheets absorb near-UV light and emit red light. The nanosheets possess high photostability under the continuous near-UV excitation. In this study, we make efforts to fabricate Y2O3:Bi3+,Eu3+fluorescent nanosheet films on ITO-coated glass substrates by electrophoretic deposition. Bi(NO3)3･5H2O (0.004 mmol) was dissolved in ethylene glycol (2.6 mL). Y(NO3)3･6H2O (0.956 mmol) and Eu(NO3)3･6H2O (0.040 mmol) were dissolved in ultrapure water (30 mL). The aqueous solution was added to the ethylene glycol solution, and then the mixed solution was mixed with triethylamine (3 mL). The total volume of the suspension was adjusted to 40 mL by adding ultrapure water, and the resulting suspension was heated in an autoclave at 160 °C . After centrifugation and freeze-drying, the powdered product was heated to 600 °C and kept at that temperature for 2 h to obtain calcined sample. The calcined sample was mixed with an aqueous solution of trisodium citrate, and stirred for 2 h. Citrate-modified nanosheets were re-dispersed to an NaOH aqueous solution (pH=11). An aqueous emulsion of silicone-modified acrylic resin was added to the nanosheet suspension as a binder. A nanosheet film was fabricated on an ITO-coated glass substrate at the anode side by application of a constant voltage in the prepared suspension. The absolute values of zeta potentials of Y2O3: Bi3+,Eu3+ nanosheets dispersed in ultrapure water increased after modification with citrate ions. The increase in zeta potentials verifies that citrate ions act as a stabilizing agent to prevent aggregation of the nanosheets. The deposited film exhibited red luminescence under UV light. According to SEM observation, the film was composed of Y2O3: Bi3+,Eu3+ nanosheets and nanoparticles of silicone-modified acrylic resin.