Mn4+ doped (NH4)2TiF6 and (NH4)2SiF6 micro-crystal phosphors: synthesis through ion exchange at room temperature and their photoluminescence properties

Abstract

The synthesis procedures of red phosphors activated by Mn⁴⁺ that are carried out especially at room temperature, are significant to industrialization. Herein, we report a facile strategy to obtain two red micro-crystal phosphors: (NH₄)₂TiF₆:Mn⁴⁺ (NTF:Mn) and (NH₄)₂SiF₆:Mn⁴⁺ (NSF:Mn) through ion exchange at room temperature for a few hours. Raw materials NTF and NSF act as host lattices of red micro-crystal phosphors, and activator Mn⁴⁺ ions are from K₂MnF₆/HF and/or mixed KMnO₄/HF solution. The reaction mechanism for the synthesis process has been comprehensively discussed in detail. The typical red emitting luminescence of Mn⁴⁺ with strong absorption in the blue region and the large size of about 200 μm of red micro-crystal phosphors NTF:Mn make it an attractive candidate material as a red compensator for resin-free white light-emitting diodes with high color rendering index. The dependence of emission intensity on concentration of HF and KMnO₄, and measurement temperature has been investigated. The advantage of the proposed strategy is the ability to explore Mn⁴⁺ doped red phosphors from low-cost starting materials at room temperature for large scale industrial applications.