Probing the local structure of the near-infrared emitting persistent phosphor LiGa₅O₈:Cr³⁺

Abstract

A combination of techniques is used to investigate the incorporation of chromium in the persistent phosphor LiGa5O8:Cr3+. Afterglow can be enhanced by codoping with Si(iv) or Ge(iv) ions.

LaAlO3:Mn4+ as Near-Infrared Emitting Persistent Luminescence Phosphor for Medical Imaging: A Charge Compensation Study

“…The spectrum consists of several sharp features, peaking at (from left to right) 697.5 nm, 704.5 nm, 710.5 nm, 718 nm, 724.5 nm and 731 nm, corresponding to the spin-forbidden 2 E g → 4 A 2g transition and the vibrational sidebands of zero-phonon line (ZPL) with phonon assistance. Due to its high effective positive charge, Mn 4+ experiences a large crystal field and hence no transitions from the 4 T 2 level are expected, in contrast to Cr 3+ -based phosphors [17]. The zero-phonon line (ZPL) is located at 718 nm in Figure 3.…”

“…Many Cr 3+ -doped phosphors are widely investigated, such as ZnGa 2 O 4 :Cr 3+ [13], Zn 3 Ga 2 Ge 2 O 10 :Cr 3+ [14], Zn 3 Ga 2 SnO 8 :Cr 3+ [15] and LiGa 5 O 8 :Cr 3+ [16,17,18]. Currently, manganese doped compounds, especially Mn 4+ -activated phosphors, are considered as a promising alternative to Cr 3+ -doped nanomaterials [19].…”

Local, Temperature-Dependent Trapping and Detrapping in the LiGa5O8:Cr Infrared Emitting Persistent Phosphor

“…The separation between the zero-phonon line and the phonon side bands falls in range from 200-400 cm −1 , in agreement with literature values obtained from FTIR and Raman spectroscopy. 19,37 The 2 E lines are situated on top of a broad emission band, from 650 nm to over 800 nm, that is due to a spin-allowed transition between the 4 T 2 state and the ground state. Thus, at each wavelength, there will be a contribution to the total emission from both the 2 E and 4 T 2 levels.…”

“…As the Cr 3+ luminescence is highly sensitive to the local surroundings in the host lattice and nearby defects, 19,[32][33][34][35] changes in the spectrum over time can reveal a specific subset of Cr ions that take part in the afterglow. Figure 6 shows the steady-state PL spectrum of LGO:Cr.…”

“…This afterglow time can be significantly improved to over 8 hours by codoping with ions with a 4+ valence, such as Si or Ge. 19 Plotting the inverse of the afterglow intensity against time reveals an approximately linear t −1 behavior for the persistent luminescence ( Figure 2). This specific decay behavior has been linked to either a detrapping mechanism from isolated traps via tunneling processes; 21 or an indication for the presence of a broad trap distribution in the phosphor.…”