Here is an SVG font for emoji, created by Pagefire. This is an SVG 1.1 Full font. It simply has multiple paths, which include gradient fills, for each glyph. Apart from that it is a standard Unicode font (Unicode added emoji in Unicode 6.0).
In this image, the font is being displayed in Batik 1.7:
Edit: thought it was obvious but just in case: those are scalable, vector glyphs, not a raster image (or worse, a bunch of raster images at 10,11,12,13,14 etc px high)