Phase‐Selective Nanocrystallization of NaLnF4 in Aluminosilicate Glass for Random Laser and 940 nm LED‐Excitable Upconverted Luminescence

Yb/Er doped hexagonal β‐NaLnF4 (Ln = Gd, Y, Lu) are regarded as the most efficient green upconversion (UC) materials. Unfortunately, β‐NaLnF4 is quite difficult to grow as monocrystal owing to cubic‐to‐hexagonal phase transition during cooling. As an alternative, herein a nanocrystallization controllable strategy to synthesize monodisperse whole‐family β‐NaLnF4 (from NaLaF4 to NaLuF4) embedded bulky glass ceramics is reported. A series of structural and spectroscopic characterizations indicate that Na content and Al/Si ratio are the most important factors to determine phase‐selective NaLnF4 crystallization in the aluminosilicate oxyfluoride glasses. Impressively, such nanocomposites are evidenced to be ideal hosts for upconversion luminescence of Yb3+/Er3+ dopants and as the proof‐of‐concept experiments, their applications in a random laser and incoherent LED‐excitable upconverting device as emitting media are demonstrated. It is expected that this study will provide a deep understanding for controllable crystallization in glass and extend the practical applications of glass ceramics in optoelectronic fields.