Laser excitation‐activated self‐propagating sintering of NaYbF4:Pr3+/Gd3+ white light microcrystal phosphors

Abstract

AbstractWe demonstrate that self‐propagating sintering reaction could be activated and dramatically enhanced by laser excitation of ion dopants in the solid‐state reactants. Near‐resonant laser absorption and subsequent nonradiative decays make the solid‐state reactants be sintered efficiently while ionic excitations catalyze self‐propagating solid‐state reactions. As a prototype demo, we synthesized white light upconversion phosphors NaYbF4:Pr3+/Gd3+. A continuous‐wave laser at 980 nm was used to populate Yb3+ ions in YbF3 to excited level, which react with NaF to preform NaYbF4 nuclei. The preformed nuclei enhanced laser excitation and energy transfer to those ions that could not be directly excited by the pump laser and thus enabled self‐propagating solid‐state sintering synthesis of NaYbF4 microcrystals at quite low laser powers. Laser excitation of Yb3+ ions could also benefit facile rare‐earth ion doping through activated self‐propagating reactions. Gd3+ and Pr3+ ions were doped in NaYbF4 by simply adding Gd3+ and Pr3+ ionic oxides or fluorides in the raw materials. In addition, Gd3+ ions doping in F− anions ambient could transform the NaYbF4 microcrystal phase from cubic to hexagonal and tune upconversion photoluminescence. This synthetic method can be widely applied to synthesize many other solid‐state compounds, perovskite solar cells, photocatalysts, solid oxide fuel cells, and so forth.