Highly efficient infrared-to-visible energy upconversion in Er^3+:Y_2O_3

Very intense green and red emission was observed at room temperature from the ${{}^{4}S}_{3/2}$ and ${{}^{4}F}_{9/2}$ levels of ${\mathrm{Er}}^{3+}:{\mathrm{Y}}_2{\mathrm{O}}_3$. A cw diode laser at 975 nm was used as a pump for resonant sequential excitation of the ${{}^{4}I}_{11/2}$ and ${{}^{4}F}_{7/2}$ levels. The fluorescence was easily visible to the naked eye, even with 27 mW of excitation power. It was found that at 850 mW of cw excitation power the total luminance was $39,000 \mathrm{cd}/{\mathrm{m}}^2$. This corresponds to $\sim 100 \mathit{\mu }\mathrm{W}$ of green emission and $270 \mathit{\mu }\mathrm{W}$ of red emission.