Single Crystal Growth and Crystal Structure Analysis of Novel Orange-Red Emission Pure Nitride CaAl₂Si₄N₈:Eu²⁺ Phosphor

Single crystal of novel orange-red emission CaAl₂Si₄N₈:Eu²⁺ phosphor was grown by our original vapor phase technique, and the precise crystal structure was investigated for the first time by single crystal X-ray diffraction analysis. The crystal structure of CaAl₂Si₄N₈:Eu²⁺ single crystal was verified to be an α-Si₃N₄-type trigonal structure (space group P31c) with a = 0.79525(9) nm, c = 0.57712(8) nm, and z = 2. The Ca atoms were coordinated to seven nitrogen atoms and located in the three-dimensional framework formed by (Al, Si)N₄ tetrahedra. The single-crystal CaAl₂Si₄N₈:Eu²⁺ phosphors exhibited a broad reddish-yellow emission with a peak at 600 nm under near-UV and blue light excitation. When increasing the temperature up to 150 °C, the emission intensity of the CaAl₂Si₄N₈:Eu²⁺ phosphor decreased to 88% of the initial value at 25 °C.