Enhanced dual-wavelength sensitive red upconversion luminescence in Bi2O3:Yb3+/Er3+ phosphors via optical-inert ions doping

A series of Bi2O3:Yb3+/Er3+ phosphors with different phases and morphologies were obtained by tuning doping ions, which played a vital role in the upconversion luminescence (UCL). Both Er3+ single doped and Yb3+/Er3+ co-doped samples exhibit narrow, nearly pure red emission whether excited by 980 nm or 1550 nm. Compared to the sum of emission intensities excited by two single-wavelength (980 nm and 1550 nm) separately, the red emission from Bi2O3:Yb3+/Er3+ with uneven distributed nanometer or micron blocky particles structure excited by two-wavelength simultaneously was enhanced by a factor of 2.41. To further improve the UCL intensity, optical-inert ions such as Na+, Ca2+ and Gd3+ were doped into this system. Compared to the optical-inert ions free sample (Bi2O3:15% Yb3+, 2% Er-3 ), the pure red UCL in Bi2O3:15% Yb3+, 2% Er3+ with 6% Na+, 2% Ca(2+ )and 4% Gd3+ doping is enhanced by 223.83 or 203.73 times under 980 or 1550 nm excitation, respectively. Meanwhile, the UCL mechanism under the multiwavelength was investigated in detail and its model of UC emission process was proposed.