Erregistroa posta elektronikoz bidali: Monodisperse Core-Shell NaYF(4):Yb(3+)/Er(3+)@NaYF(4):Nd(3+)-PEG-GGGRGDSGGGY-NH(2) Nanoparticles Excitable at 808 and 980 nm: Design, Surface Engineering, and Application in Life Sciences