A novel composite phosphor via one-pot synthesis: Single matrix with controllable luminescence

A new promising phosphor material established on Eu3+ doped monoclinic (SrAl2Si2O8)/tetragonal (Sr2Al2SiO7) composite with controllable photoluminescence (PL) has been successfully synthesized using one-pot processing technology. Completely phase-separated SrAl2Si2O8/Sr2Al2SiO7 can be achieved in a single matrix starting from single-source precursors. In this work, a series of composite phosphor samples (including 50 mol%(SrAl2Si2O8)–50 mol%(Sr2Al2SiO7): 2, 6, 10, and 14 mol% Eu) were obtained after thermal treatment at 1300 °C for 36 h. The SrAl2Si2O8/Sr2Al2SiO7:Eu composites yield red (c. 616 nm) and blue (c. 440 nm) emission light when excited by near-UV 380 nm light. The crystal structures were investigated by X-ray diffraction after phase separation, and showed relatively small changes in lattice parameters. X-ray photoelectron spectroscopy and electron paramagnetic resonance for the composites showed red and blue emissions originating from Eu3+ and Eu2+ ions, which served as two different but coexisting activators due to the different crystal structural characteristics in Sr2Al2SiO7 and SrAl2Si2O8, respectively. The energy transfer between Eu3+ and Eu2+ in the same matrix tends to cause the alternating changes in the relative intensity of red and blue emitting lights with varied Eu concentration. As a result, controllable luminescence over the whole visible region can be obtained by doping appropriate rare earth contents or tailoring initial compositions of the precursors.