Improved photon upconversion photoluminescence and intrinsic optical bistability from a rare earth co-doped lanthanum oxide phosphor via Bi3+ doping

Abstract

In this paper, an Er³⁺, Yb³⁺ co-doped La₂O₃ phosphor has been synthesized through a solid state reaction method. Structural analysis reveals the strong crystalline nature of samples. EDS measurements confirm the presence of La, O, Er, Yb and Bi elements in the sample. FTIR measurements of samples show bands due to La–O stretching vibrations. UV-vis-NIR spectra of samples show a large number of absorption bands due to different transitions of Bi³⁺, Er³⁺ and Yb³⁺ ions. The intensities of the absorption bands increase over the entire region due to Bi³⁺ doping. The phosphor sample emits intense green and weak red upconverted photoluminescence centered at 523 and 671 nm, respectively, upon excitation at 976 nm. The emission intensity of the phosphor is optimum for a 0.7 mol% Er³⁺ ion concentrations. Pump power versus emission intensity studies shows the absorption of two photons for this upconverted emission and color tunability. The emission intensity of the Er³⁺, Yb³⁺ co-doped La₂O₃ phosphor is enhanced up to ∼65 times as a result of Bi³⁺ doping. The enhancement in emission intensity is observed due to an increase in crystallinity and the intensity of the absorption bands. The Er³⁺, Yb³⁺ co-doped La₂O₃ phosphor also shows intrinsic optical bistability (IOB) and the area of the IOB curves increases significantly following Bi³⁺ doping. Thus, the Er³⁺, Yb³⁺, Bi³⁺ co-doped La₂O₃ phosphor may be used in photonic and optically bistable devices.