Synthesis and luminescence of Sr 2 Ta 2 O 7 :Pr 3+ : a novel blue emission, long persistent phosphor
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In this paper, a novel afterglow phosphor based on praseodymium ion doped Sr2Ta2O7 was synthesized successfully by solid-state reaction in the ambient atmosphere. The photoluminescence, afterglow, afterglow decay, and thermoluminescence (TL) properties were investigated in detail. The dependence of photoluminescence properties and long afterglow (LAG) performances on Pr31 contents were investigated systematically. The optimal concentrations of Pr31 ions for the best photoluminescence and LAG properties were experimentally to be 2 mol% and 0.5 mol%, respectively. Pr31 exhibits prominent red emission in most reports, which derives from the 1D2 ! 3H4 transition. However, the predominant blue emission locating at ;489 and ;507 nm coming from 3P0,1 ! 3H4 transitions were observed in praseodymium ion-doped Sr2Ta2O7. Based on TL measurements, the trapping and de-trapping processes of charge carriers between shallower and deep traps were illustrated. A model was proposed on the basis of experimental results to explain the mechanisms of photoluminescence and LAG.
I. INTRODUCTION
Recently, long persistent phosphors (LPP) have attracted a lot of attention due to their interesting optical phenomenon that can emit light for a long time after removal of the excitation source.1–3 Such a unique phenomenon possesses many advantages such as energy saving, environmentally friendly, and recyclable; therefore, it can be widely applied in various fields, such as but not limited to, decoration, emergency signs, traffic signs, emergency exit indicators, low level lighting, imaging storage, detection of high energy rays, etc.4–9 Generally, emitter and trap are the most important functional centers in LPP. Traps are produced by the defects in the doping and synthesis process, usually do not emit radiation by themselves, instead they store excitation energy which can be gradually released under thermal or other physical stimulations and then be transferred to the emitters. Emitters are mostly rare earth ions or transition metals ions such as Pr31, Tb31, Eu31, Eu21, Sm31, Dy31, Ce31, Mn21, and Cr31, etc.,10–12 which are capable of emitting radiation after being excited. Herein, Pr31 ions, which can produce light emitting or long afterglow (LAG) via f–f transition in the blue, green, red regions depending on the crystal lattice of hosts for luminescence materials, were chosen as the luminescence activators for LPP in this work. Contributing Editor: Winston V. Schoenfeld a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.401
With the exploration of luminescent materials, more and more matrixes have been reported, consisting of silicates, aluminum, stannates, borates, phosphates, titanates, sufides, molybdates, tungstate, and vanadates etc.13–16 But there are few related reports about tantalite. The tantalite compound is currently playing an important role in the field of photocatalysis, where it is used to decompose water molecules into H2 and O2 molecules.17–19 Recently, layered perovskite Sr2Ta2O7 has at
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