“…In order to realize favorable optical performance, the host materials, where Ln 3+ ions reside, should be appropriately selected, because the radiative and nonradiative transitions as well as energy transfer of Ln 3+ ions are highly dependent on the crystalline field surrounding them. Till now, large number of rare earth inorganic compounds, including oxides [10,11], oxysulfides [12,13], oxyfluorides [14,15], sulfides [16], fluorides [17][18][19], chlorides [20,21], phosphates [22] and vanadates [23], have been selected as host materials for the doping of rare earth ions. Among the as-reported host materials, Ln 3+ -doped fluorides with general formula NaLnF 4 , possessing low phonon energy, good optical transparency and adequate thermal and environmental stability, have been regarded as excellent host lattices for achieving desirable optical performance.…”