The first principles calculation and temperature-sensitive luminescence behavior of optimized red phosphor Mg2Al4Si5O18: Eu3+

Abstract

Eu3+ doped Mg2Al4Si5O18 phosphors were prepared by the solid-state reaction. The first principles calculation, XRD, diffuse reflection spectra, photoluminescence spectra and thermal quenching are carried out to investigate the electron structure, crystal structure, photoluminescence and thermal properties. The calculation results show that Mg2Al4Si5O18 possesses the direct band gap of about 5.1eV. With the introduction of Eu3+, the energy gap becomes obviously smaller due to the discontinuity of exchange-correlation energy. Between HOMOs and LOMOs, a series of f orbitals of Eu3+ can be observed, which is the essential condition to realize the efficient 4f–4f transitions of Eu3+. The experimental results indicate that the samples can efficiently absorb the UV-light and emit the red light with the highest peak at 614nm. With the co-doping of Bi3+ as sensitizer, the emission intensity of Eu3+ increases by about 49% due to the energy transfer between Bi3+ and Eu3+. With the introduction of Li+/Na+/K+ as charge compensators, the emission intensities of Mg2Al4Si5O18: Eu3+ are enhanced by about 22%, 18% and 5%. With the temperature increase, the emission intensity of all samples, especially the Bi3+ doped samples, dramatically declines, which reveals two important effects: one is that the Eu3+ emission is very sensitive to temperature, and other is that the complex energy transfer process among the excited and ground states of Eu3+, Bi3+ or host absorption occurs. To explain the degradation, the mechanism based on the configurational coordinate diagram is proposed and this model could be helpful for the understanding of the energy transfer mechanism among the various energy levels in the process of temperature change.