Light-emitting device and related projection system

The embodiment of the invention discloses a light-emitting device which comprises an excitation light source and a wavelength conversion device. The excitation light source is used for emitting excitation light, and the optical power density of the excitation light is larger than 35 w/mm . The wavelength conversion device comprises fluorescent powder which is located on the light path of the excitation light emitted by the excitation light source, the fluorescent powder is used for absorbing the excitation light to emit excited light, the average afterglow time of the excited state of the fluorescent powder is shorter than or equal to 0.1 microsecond, and the dominant wavelength of the excited light is bigger than or equal to 580 nm. The embodiment of the invention further provides a related projection system of the light-emitting device, and the light-emitting device is higher in luminous efficiency and capable of replacing red light.