Preparation of Eu2+-doped Ca2Si5N8 by carbothermal reduction/nitridation of spray-pyrolyzed oxide/nitride powder and its luminescence properties

The conditions for the preparation of regular-shaped Eu2+-doped calcium silicon nitride ((Ca0.99Eu0.01)2Si5N8) powder were examined by the carbothermal reduction and nitridation (CRN) of oxide/nitride powder prepared by ultrasonic spray pyrolysis. Two kinds of silicon sources, i.e., (i) colloidal silica (CS) and (ii) silicon nitride (Si3N4; SN), were used for the spray pyrolysis. Firstly, the solution containing 0.057 mol·m-3 Ca(NO3)2, 0.140 mol·dm-3CS and 5.71 x 10-4 mol·dm-3Eu(NO3)3 was spray-pyrolyzed at 600°C, and the resulting powder was calcined at 800°C for 10 min in air. The single phase but agglomerated particles of (Ca0.99Eu0.01)2Si5N8 were obtained when the CRN (the relative carbon amount to the stoichiometric amount (m): 1.5) of spray-pyrolyzed/calcined oxide powder was conducted at 1300°C for 2 h in nitrogen (N2) atmosphere. Secondly, the solution containing 0.0285 mol·dm-3Ca(NO3)2, 0.070 mol·dm-3SN and 2.855 x 10-4mol·dm-3Eu(NO3)3 (one-half of the solution concentration compared to the case of CS utilization) was spray-pyrolyzed, and the CRN of spray-pyrolyzed oxide/nitride powder was conducted at 1500°C for 2 h to obtain (Ca0.99Eu0.01)2Si5N8 in N2 atmosphere. The microscopic observation showed that this powder was composed of regular-shaped particles with sizes of approximately 2-3 µm. The excitation and emission peaks of this powder appeared at around 370 and 590 nm, respectively, showing the emission of orange light.