FIG. 1. (a) Emission spectra measured under the excitation of 980 nm IR laser for CeO2:Ho3+ and CeO2:Ho3+/Yb3+ particles prepared by spray pyrolysis and (b) energy-level diagram for Ho3+ and Yb3+ ions.
FIG. 3. SEM photos of CeO2:Ho3+/Yb3+ powder prepared by spray pyrolysis: (a) as-prepared, (b) 900℃, (c) 1000℃, (d) 1100℃ and (e) 1200℃. (f) Particle formation mechanism in spray pyrolysis.
FIG. 4. Concentration effect of Ho3+ and Yb3+ on the upconversion properties of Ce1-x-yO2:xHo3+/yYb3+: Emission spectra (a and b) and three-dimensional plot of the green emission intensity (c) while changing the amount of Yb3+ and Ho3+ ions. All samples are calcined at 1200℃.
FIG. 5. Linear plots between of (a) ln(I/x or I/y) against ln(x or y) and (b) ln(I/(x+y)) versus ln(x+y) for Ce1-x-yO2:xHo3+/yYb3+.
FIG. 6. (a) Upconversion emission spectra at different pumping power and (b) logarithmic dependence of green peak intensity as a function of pumping power for CeO2:Hox3+/Yby3+ (x = 0.003, y = 0.02). Changes in the n value as a function of (c) Yb3+mol%, (d) Ho3+ mol% and (e) Yb3+/Ho3+ mole ratio.
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