Absorption spectra of the crystal at .
Energy level diagram of ions in the PWO crystal. The possible upconversion emission mechanisms under excitation are indicated.
(Color online) Upconversion emission spectra of crystal pumped by at (a) room temperature and (b) . Three parts of emission in (b): UV , blue , and green regions are obtained using different pumping energies of 0.06, 0.04, and /pulse, respectively.
(Color online) Upconversion and Stoke’s emission spectra in obtained at different temperatures by 355 and pumping into the level and the level, respectively.
(Color online) Excitation spectra obtained by monitoring the 443 and emissions in the region, corresponding to the absorption for , , and levels at .
Emission spectra of the transition in -doped PWO crystal under the excitation at at .
Luminescence decay of the transition in the -doped PWO crystal with excitation at .
Logarithmic plots of the upconversion emission intensity vs the pumping power at .
(Color online) (a) Excitation spectrum for the upconversion emission of and (b) absorption spectrum corresponding to the transition at .
(Color online) Decays obtained by collecting the luminescence from the level at , exciting the sample at 355, 532, and , in resonance with the , , and levels, respectively.
(Color online) (a) Excitation spectrum for the upconversion emission of and (b) absorption spectrum corresponding to the transition at room temperature.
(Color online) Experimental decays obtained at by collecting the luminescence of by exciting the sample at 532 and , in resonance with the and levels, respectively. The symbols correspond to experimental data and the solid line is the fit to a single exponential.
Lifetimes of emissions of ions in the PWO crystal excited by 355, 532, and at 10 and
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