Spontaneous recurrent hemarthrosis of the knee joint in the elderly: a report of two cases

High efficient red phosphor K2TiF6:Mn4+ was successfully prepared though a modified two-step co-precipitation method under room temperature. Pure phase of the K2TiF6 powder, with various doping concentration of Mn4+ range from 4 at.% to 9 at.%, was determined by the X-ray diffraction (XRD) analysis. The Mn4+ ions were clearly detected by the X-ray photoelectron spectroscopy (XPS) measurement and the electron paramagnetic resonance (EPR). The average particle size, i.e. D50, is around ⿼30 μm scanned by laser particle size analyzer. The highest emission peak centered at about 633 nm was observed from the photoluminescence spectra. The 6 at.% concentration of Mn4+ shows the best internal emission efficiency of around 99%, which also gives the excellent thermal quench performance. We demonstrated that the maximum color rendering index (CRI) was 85.1 with luminous efficiency as high as 143.82 lm/W, indicating that K2TiF6:Mn4+ phosphors had a promising potential for white light-emitting diodes (WLEDs).