“…The former is a high-temperature metastable phase, while the latter remains thermodynamically stable [7,8]. The past decades have witnessed much exploration of its controlled synthesis and up-/down-conversion luminescent properties [1,4,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34]. Compared with considerable work on Ī±āĪ² phase transformation [1,4,9,10,11,12,13,14,15,16,17,18,19], the fabrication of Ī±-NaYF 4 as well as the investigation involving the Ī²āĪ± transformation process have been neglected [26,30,33,34].…”