Preparation of Novel Rare-Earth-Doped (Oxy)Nitride Phosphor and Evaluation of Characteristics

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In this work, Eu^<2+>-doped alkaline earth silicon nitride (Ca_2Si_5N_8 : 1mol% Eu^<2+> ; (Ca_<0.99>Eu_<0.01>)_2Si_5N_8) was synthesized by carbothermal reduction and nitridation of (oxy) nitride/oxide powder prepared by ultrasonic spray pyrolysis (USP-CRN). The starting solution (0.1mol・dm^<-3>) containing Si_3N_4, Ca(NO_3)_2 and Eu(NO_3)_3 ((Ca+Eu)/Si ratio=0.4) was spray-pyrolyzed at 600℃. After the spray-pyrolyzed powder was mixed with carbon (the ratio of carbon amount to stoichiometric amount ; 1.50), the mixture was heated at a temperature between 1400 and 1550℃ for 2h in N_2 atmosphere. A single phase of Ca_2Si_5N_8 could be obtained when the mixture had been carbothermally nitrided at and above 1500℃. Moreover, the synthesis of (Ca_<0.99>Eu_<0.01>)_2Si_5N_8 was conducted by the USP-CRN technique, using colloidal silica (SiO_2 ; CS), and solid-state reaction (SSR) and CRN. When the black light was irradiated to the (Ca_<0.99>Eu_<0.01>)_2Si_5N_8, the orange light was emitted. The relative emission intensities, compared to the case of YAG, i.e., the standard substance : Y_3Al_5O_<12>:Ce^<3+> (YAG), were : 0.494 (SSR-CRN)>0.452 (USP-CRN : utilization of Si_3N_4 as Si source)>0.0371 (USP-CRN ; utilization of CS as Si sourse). The relative emission intensity of (Ca_<0.99>Eu_<0.01>)_2Si_5N_8) prepared by USP-CRN, using Si_3N_4 as Si source, was almost comparable to that prepared by SSR-CRN. SEM micrograph of this powder heated at 1500℃ for 2h in N_2 atmosphere showed the spherical particles with diameters of around 2・m. Such particles are expected to be available as a phosphor for white-light LED.