Comparative study of red-emitting pyrophosphate phosphors: Site-selective replacement of Eu3+and luminescent properties

Red phosphors play a key role in improving the optical quality of white light emitting diodes (WLEDs). In this work, Eu3+-activated red-emitting pyrophosphate phosphors of NaREP2O7:Eu3+ (RE = Sc, Lu) were prepared and the comparative investigations on crystal structures and luminescent properties were carried out. The X-ray diffraction (XRD), scanning electron microscope (SEM), and spectroscopy techniques were employed to char-acterize the materials. The features of crystal structures with regard to the Eu3+ doping were analyzed in detail on the basis of Rietveld crystal structure refinements. It is found that the Eu3+ tends to substitute Lu3+ in the NaLuP2O7:Eu3+, while in NaScP2O7:Eu3+ it tends to substitute Na+ due the principle of ionic size matching. The disparate selective occupation behaviour of Eu3+ ion in both crystals has resulted in a certain difference in fluorescence emission nature from each other. The doping concentration of Eu3+ was optimized for the strongest luminescence under near-ultraviolet (UV) excitation. The measurement of temperature-dependent luminescence showed that the emission of NaLuP2O7:Eu3+ at 150 degrees C maintained 77% of that at room temperature, and that for NaScP2O7:Eu3+ is 72%. Under the near-UV excitation, the fluorescence efficiency of the phosphors were assessed. The quantum efficiencies of NSPO:0.125Eu3+ and NLPO:0.125Eu3+ were measured to be 41.6% and 40.8%, respectively. The results imply that the Eu3+-activated pyrophosphate phosphors are promising red-emitting components in WLEDs.