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

Abstract

The near-infrared emitting persistent phosphor LiGa 5 O 8 :Cr 3+ (LGO:Cr) has promising applications in bioimaging. In order to improve the persistent luminescence of LGO:Cr and other Cr-doped persistent phosphors, a better understanding of trapping and detrapping mechanisms is necessary. In this work, we study the afterglow and thermoluminescence via a thermal fading experiment. The results show that there is a broad trap distribution present in LGO:Cr. The emission spectrum of chromium changes during the afterglow, which indicates that different Cr ions experience a varying crystal field in the LGO host, due to different defect configurations, and that the detrapping process occurs locally. The results of thermoluminescence and spectral decay measurements show that chromium ions residing near deep traps are subject to a smaller crystal field. Vacancies formed during the synthesis are most probably causing this effect. Codoping LGO with Si 4+ or Ge 4+ significantly improves the persistent luminescence and increases the number of deep-lying traps in the phosphor.

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

“…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].…”

Identifying Near‐Infrared Persistent Luminescence in Cr3+‐Doped Magnesium Gallogermanates Featuring Afterglow Emission at Extremely Low Temperature

“…For most room‐temperature persistent phosphors, there is no obvious decrease of the TL signal from fading experiments at low temperature due to the very slow detrapping. For example, from the TL fading experiments of an NIR emitting persistent phosphor LiGa 5 O 8 :Cr 3+ reported by De Clercq et al, the shape and intensity of the TL peak remained constant for the fading at −60, −40, and −20 °C. In addition, the intense signals of starting points of TL glow curve with no fading also prove the strong afterglow intensity because these starting points originate from both TL signals and low‐temperature persistent luminescence.…”

Biocompatible Lipid‐Coated Persistent Luminescent Nanoparticles for In Vivo Imaging of Dendritic Cell Migration

“…Stoichiometric amounts of Li 2 CO 3 and Ga 2 O 3 were used as precursor materials. Cr 3+ doping was achieved by adding 1 mol% Cr 2 O 3 with respect to the Ga content . The precursor mixture was ground thoroughly in an agate mortar and transferred to an alumina crucible.…”

“…They can store charge carriers in defects inside the material, i.e., so‐called energy traps. Trapped charge carriers can then slowly escape from these defects over time and migrate back to recombination centers where radiative decay can occur, resulting in persistent luminescent behavior, also called “afterglow.” Aimed at long‐term in vivo imaging of DC migration, a particularly interesting persistent phosphor with an excellent signal‐to‐noise (S/N) ratio is LiGa 5 O 8 :Cr 3+ (LGO:Cr 3+ ), which has very long persistent luminescence of more than 1000 h after UV illumination in the NIR‐1 window . An interesting feature of LGO:Cr 3+ is that the duration of the afterglow can be repeatedly extended by optical stimulation with a simple white light‐emitting diode (LED) flashlight, which causes a new burst of light by releasing remaining energy stored in energy traps .…”