Template-free hydrothermal preparation of IR-blue light upconverting NaYF4: Yb, Eu phosphors - Ruiz-Santaquiteria, Cristina; Calatayud, David G; Gutierrez, Kevin; Villegas, Marina; Peiteado, Marco; Jardiel, Teresa (Boletin De La Sociedad Espanola De Ceramica Y Vidrio, 2024)