Valence and environment of rare earth ions in CaAl2O4:Eu2+,R3+ persistent luminescence materials

Hölsä, Jorma; Laamanen, Taneli; Lastusaari, Mika; Malkamäki, Marja; Welter, Edmund; Zając, D.

doi:10.1016/j.sab.2009.12.007

Cited by 46 publications

(20 citation statements)

References 25 publications

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“…For this reason, CaAl 2 O 4 :Eu is often chosen as a standard material for persistent luminescence investigations. 41,52,[57][58][59][60][61][62][63] …”

Section: Trap Depth Distribution In Caal 2 O 4 :Eundmentioning

confidence: 99%

Revealing trap depth distributions in persistent phosphors

et al. 2013

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Persistent luminescence or afterglow is caused by a gradual release of charge carriers from trapping centers. The energy needed to release these charge carriers is determined by the trap depths. Knowledge of these trap depths is therefore crucial in the understanding of the persistent luminescence mechanism. Unfortunately, the trap depths in persistent phosphors are often difficult to evaluate in an accurate and reliable way. The existing analysis methods are mostly based on single experiments, or they ignore the possibility of a continuous distribution of trap depths. We present a procedure to accurately probe the activation energies, even in the presence of a continuous distribution of energy levels. By performing a series of thermoluminescence experiments with varying excitation duration and at varying excitation temperature, and employing the initial rise analysis method, the depth and shape of such a distribution can be estimated. As an example, we investigated the trap system in the violet persistent phosphor CaAl 2 O 4 :Eu,Nd, and show that it consists of a Gaussian-shaped distribution of trap depths. The maximal density of traps lies in the region around 0.9 eV, but the distribution extends to 0.7 eV on the shallow side and 1.2 eV on the deep side. The described procedure can be used to obtain a clear view of the trap system in other persistent phosphors as well. This can lead to a better understanding of the nature of these trapping centers, and the role they play in the persistent luminescent mechanism.

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“…For this reason, CaAl 2 O 4 :Eu is often chosen as a standard material for persistent luminescence investigations. 41,52,[57][58][59][60][61][62][63] …”

Section: Trap Depth Distribution In Caal 2 O 4 :Eundmentioning

confidence: 99%

Revealing trap depth distributions in persistent phosphors

et al. 2013

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“…This makes it a versatile tool to study persistent luminescent materials since the dopant concentration will usually be very low. [18][19][20][21][22][23][24][25][26][27][28] …”

Section: Introductionmentioning

confidence: 99%

The importance of inversion disorder in the visible light induced persistent luminescence in Cr³⁺doped AB₂O₄(A = Zn or Mg and B = Ga or Al)

Basavaraju

Priolkar

Gourier

et al. 2015

Phys. Chem. Chem. Phys.

136

110

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Cr 3+ doped spinel compounds AB 2 O 4 with A=Zn, Mg and B=Ga, Al exhibit a long near infrared persistent luminescence when excited with UV or X-rays. In addition, persistent luminescence of ZnGa 2 O 4 and to a lesser extent MgGa 2 O 4 , can also be induced by visible light excitation via 4 A 2 → 4 T 2 transition of Cr 3+ , which makes these compounds suitable as biomarkers for in vivo optical imaging of small animals. We correlate this peculiar optical property with the presence of antisite defects, which are present in ZnGa 2 O 4 and MgGa 2 O 4 . By using X-ray absorption fine structure (XAFS) spectroscopy, associated with electron paramagnetic resonance (EPR) and optical emission spectroscopy, it is shown that an increase in antisite defects concentration results in a decrease in the Cr-O bond length and the octahedral crystal field energy. A part of the defects are in the close environment of Cr 3+ ions, as shown by the increasing strain broadening of EPR and XAFS peaks observed upon increasing antisite disorder. It appears that ZnAl 2 O 4 , which exhibits the largest crystal field splitting of Cr 3+ and the smallest antisite disorder, does not show considerable persistent luminescence upon visible light excitation as compared to ZnGa 2 O 4 and MgGa 2 O 4 . These results highlight the importance of Cr 3+ ions with neighboring antisite defects in the mechanism of persistent luminescence exhibited by Cr 3+ doped AB 2 O 4 spinel compounds.

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“…22 However this valence state change was disproved by the same group when they observed no signature of Eu 3+ oxidation state in the XANES spectra. 23 25 In a previous paper, we had presented EXAFS results along with optical and electron paramagnetic resonance (EPR) studies on Cr 3+ doped AB 2 O 4 spinels (A=Zn, Mg and B=Ga, Al). 17 In there, the crucial role of inversion defects in necessitating the persistent luminescence in spinels specially with visible light excitation was illustrated in detail.…”

Section: Introductionmentioning

confidence: 99%

Order and disorder around Cr³⁺ in chromium doped persistent luminescent AB₂O₄ spinels

Basavaraju

Priolkar

Gourier

et al. 2015

Phys. Chem. Chem. Phys.

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X-ray absorption near edge structure (XANES) spectroscopy technique is used to better understand the charging and decharging processes of the persistent luminescence in the Cr 3+ doped AB 2 O 4 spinels (A = Zn, Mg and B = Ga and Al) with low photon energy excitation by visible light. Cr K edge XANES spectra have been simulated for different near neighbour environments around the Cr 3+ recombination centres and compared with the experimental curve. In Cr 3+ :ZnGa 2 O 4 compound, the Cr 3+ local structure corresponds mostly to that of a normal spinel (∼70%), while the rest comprises of distorted octahedral environment arising from cationic site inversion and a contribution from chromium clustering. This local structure is strongly different in Cr 3+ :MgGa 2 O 4 and Cr 3+ :ZnAl 2 O 4 where, for both cases, chromium clustering represents the main contribution. The strong correlation between the intensity of persistent luminescence and % of Cr in clusters leads us to infer that presence of Cr clusters is responsible for decrease of the intensity of the visible light induced persistent luminescence in the Cr 3+ doped AB 2 O 4 spinels.

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Valence and environment of rare earth ions in CaAl2O4:Eu2+,R3+ persistent luminescence materials

Cited by 46 publications

References 25 publications

Revealing trap depth distributions in persistent phosphors

Revealing trap depth distributions in persistent phosphors

The importance of inversion disorder in the visible light induced persistent luminescence in Cr³⁺doped AB₂O₄(A = Zn or Mg and B = Ga or Al)

Order and disorder around Cr³⁺ in chromium doped persistent luminescent AB₂O₄ spinels

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Valence and environment of rare earth ions in CaAl2O4:Eu2+,R3+ persistent luminescence materials

Cited by 46 publications

References 25 publications

Revealing trap depth distributions in persistent phosphors

Revealing trap depth distributions in persistent phosphors

The importance of inversion disorder in the visible light induced persistent luminescence in Cr3+doped AB2O4(A = Zn or Mg and B = Ga or Al)

Order and disorder around Cr3+ in chromium doped persistent luminescent AB2O4 spinels

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The importance of inversion disorder in the visible light induced persistent luminescence in Cr³⁺doped AB₂O₄(A = Zn or Mg and B = Ga or Al)

Order and disorder around Cr³⁺ in chromium doped persistent luminescent AB₂O₄ spinels