Competitive Cr³⁺ occupation in persistent phosphors toward tunable traps distribution for dynamic anti‐counterfeiting

Abstract

Red/near infrared (NIR) long persistent phosphors have received extensive attentions in biomedical, food inspection, iris recognition, biological imaging, etc. Herein, a new phosphor, Li 2 ZnGe 3 O 8 :Cr 3+ , is reported with deep red persistent luminescence peaking at 708 nm. By adjusting the Cr 3+ doping concentration, the competitive site occupation at [ZnO6] and [GeO6] polyhedral enables different traps behaviors including trap types, trap concentration and trap depth, which in turn leads to different afterglow duration time from 2 to 20 h. The persistent luminescence mechanisms originated from different trap models have been discussed, and it is found that they can cooperate or inhibit each other, enabling different luminescence depending on time. The dynamic anti-counterfeiting applications have been demonstrated, which provides a new way to rationally designing for multi-functional luminescent materials.

A novel cyan-emitting phosphor KScSrSi2−yGeyO7:0.07Bi3+ for white LEDs with high color rendering index and low correlated color temperature

“…The above reaction process can be expressed as the following formula (eqn 3):In the third case, when Bi 3+ occupies both Sr 2+ and K + sites, two kinds of electronic defects are generated, namely and , and a balanced oxygen gap is generated inside. The above process can be expressed by the following defect equation (eqn 4): 33 Therefore, after the activating Bi 3+ ions enter KSSS, several irregular peaks appear in the TL spectra due to the electron defects or oxygen vacancy defects caused by non-equivalent substitution. When Si 4+ in KSSS is replaced by Ge 4+ , Bi 3+ occupies the Sc site, and Sc 3+ and Bi 3+ are equivalent substitutes; therefore, the number of defects will rapidly decrease or even disappear, reducing the corresponding peak in the spectrum.…”

Garnet-structured persistent luminescence phosphor Ca3Al2Ge3O12:Cr3+ for dynamic anticounterfeiting applications

“…Generally, the crystal field strength of octahedra is stronger than that of the dodecahedron, and a strong crystal field corresponds to high emission energy, so peak 1 and peak 2 come from the octahedra, and peak 3 and peak 4 come from the dodecahedron. 18,19 In addition, because the electronegativity of Al (1.48) > Ca (1.00), the covalence of AlO6 is less than that of CaO8, and the Nephelauxetic effect of AlO6 is less than that of CaO8 20 . In other words, the energy required to jump from the ground state to the excited state: (AlO6) > (CaO8), which also means that peak 1 and peak 2 are from the octahedron, and peak 3 and peak 4 are from the dodecahedron.…”

“…2a shows the afterglow intensity of CAG: x Cr 3+ monitored at 722 nm as a function of time; it can be visibly seen that the afterglow intensities of the samples with different concentrations are maintained at a certain level when decaying to about 600 s. The inset demonstrates the afterglow decay rates of different samples, where the value of I 0 / I 600 is the decay amount of LPL intensity during the process. The following formula can be used to calculate the afterglow decay rate of different samples 20 . I = ( I 0 − I 600 )/ I 0 …”

“…The inset demonstrates the afterglow decay rates of different samples, where the value of I 0 /I 600 is the decay amount of LPL intensity during the process. The following formula can be used to calculate the afterglow decay rate of different samples 20 .…”

Achieving Persistent Luminescence Performance Based on the Cation-Tunable Trap Distribution

“…In our previous work, by adjusting the doping concentration of Cr 3+ ions, LZG exhibited a bright-red PersL emission with a peak of 698 nm for 20 h. The analysis of PersL decay curves and TL spectra of a series of samples reveals that the PersL luminescence mechanism of LZG:Cr involves two channel models (conduction band (CB) channel and tunneling (TN) channel) through which carriers pass [32]. The PersL emission generated by the carrier of the CB channel is very bright but short, while the PersL generated by the carrier dominated by the TN channel is slow but relatively dark.…”