Erbium by itself will emit, though it may not be the highest intensity.  I know I worked with something that had higher intensity, but we just called them UCNPs (up-converting nanoparticles). I think it was a combination of Ytterbium and Erbium? I'll see if I can find a paper on it.  Also we used a 532 nm green laser, if that helps. Erbium absorbs there.

I tried Er and Yb  in LiSrBo3 host. But I didn't get intense uc

Some papers that might be useful:

"Amplified stimulated emission in upconversion nanoparticles for super-resolution nanoscopy" (They used thulium.)

"Emission stability and reversibility of upconversion nanocrystals" (They used Yb and Er.)

http://www.nature.com/nature/journal/v543/n7644/full/nature21366.html?foxtrotcallback=true

http://pubs.rsc.org/en/content/articlelanding/2016/tc/c6tc02990f#!divAbstract