Fig. 1. Emission spectra of the macroporous LN:Er sample at different excitation intensities (30 and 70  kW/cm2, inclination angle: 30°). The inset is an AFM image of the sample.

Fig. 2. Integrated emission intensity as a function of the excitation intensity on a log-log scale for (a) macroporous and (b) bulk LN:Er. The intensities were integrated from 520 to 570 nm (green-light-emission band). Solid lines are the pertinent linear fits.

Fig. 3. Emission spectrum of macroporous LN:Er at 20° from the sample surface (pump intensity: 70  kW/cm2).

Fig. 4. Energy levels of Er3+ showing the ESA and ETU pathways under pumping by a 980 nm.