“…Selecting a suitable host is a key factor for upconversion luminescent materials. It is well known that TeO 2 (optical fibers, crystals and glassy) are suitable host materials due to their lower phonon frequency, chemical durability and thermal stability [20][21][22][23][24][25][26][27][28][29]. The conventional processing is using bulk TeO 2 or TeO 2 glasses as the host materials for preparing upconversion luminescent materials [9,30,31] [31].…”