Novel bismuth silicate based upconversion phosphors: Facile synthesis, structure, luminescence properties, and applications

Abstract

A series of novel bismuth silicate Bi4Si3O12:Yb3+/Ln3+ (Ln = Er, Tm, Ho) upconversion (UC) phosphors have been synthesized via a simple sol-gel approach. The crystal structure, composition, and luminescence properties of the samples are investigated by means of XRD, FT-IR, EDX, SEM, TG-DTA, UC luminescence spectra, and decay curves, respectively. Under NIR light excitation, the Yb3+/Er3+, Yb3+/Tm3+, and Yb3+/Ho3+-doped Bi4Si3O12 samples exhibit characteristic green, blue, and red emissions, respectively. Moreover, the detailed UC mechanisms of the Bi4Si3O12:Yb3+/Ln3 phosphors were proposed on the basis of the energy level diagrams. Taking into account the dependence of UC emission intensities on the doping concentrations of Ln3+ ions, the optimal doping concentrations of Yb3+, Er3+, Tm3+, and Ho3+ are determined to be 15, 0.5, 0.4, and 4 mol%, respectively. The light-emitting diode (LED) devices have been fabricated by integrating the Bi4Si3O12:Yb3+/Ln3+ phosphors with NIR chips. The as-obtained LED devices exhibit visible light emissions with different colors coming from different Ln3+ ions under an injection current. The result indicates that the as-synthesized Bi4Si3O12:Yb3+/Ln3+ (Ln = Er, Tm, and Ho) UC luminescent materials may find potential applications in solid state lighting and optoelectronic devices.