a phosphor can be excited by light emitting diode to emit a red light . the phosphor has high emission efficiency . owing to a sensitizer is used in the phosphor , the phosphor can be excited at the wavelength of 380 ˜ 400 nm . moreover , the excitation efficiency of the wavelength shorter than 370 nm can be increased . the phosphor has a chemical formula of a 1 - x - y - z bi x b y c z moo 4 .