Deep insight on two luminous mechanism and optical properties of Pr doped MgGeO3 red/NIR luminescent materials

In this work, MgGeO3:Pr3+ system is prepared by high-temperature solid phase method under the condition of different temperature and Pr content. MgGeO3:Pr3+ could emit 622 nm (red), 716 nm (red), 903 nm (NIR) and 1081 nm (NIR) lights under the external excitation of 251 nm and 425–500 nm. Due to the different excitation wavelengths, MgGeO3:Pr3+ has completely different electronic transition paths, resulting in a much larger emission intensity under 251 nm excitation than that excited by 425∼500 nm. When the incident light wavelength is 251 nm, the excitation process is VB→1D2 level of Pr3+, and the emission is due to transition of 1D2→3H4, 1D2→3H5, 1D2→3H6(3F2) and 1D2→3F3,4. When the wavelength of incident light is 425∼500 nm, the excitation process is 3H4→CB, the emission is CB→1D2, and then 1D2→3H4, 1D2→3H5, 1D2→3H6(3F2) and 1D2→3F3,4. At the same time, the emission spectrum and X-ray diffraction measurements show that the most fundamental factor determining the emission intensity of the sample is the concentration of the luminescent center (Pr3+ that can emit light) in the MgGeO3 grain. Increasing the sintering temperature and Pr element content in raw materials can increase the of Pr3+ concentration in the grain (increase the concentration of the luminescent center). However, if the concentration of Pr3+ in the grain is too high, Pr3+ would lose the function of the luminescence center, resulting in a decrease in the concentration of the luminescence center, thereby reducing the luminescence intensity.