%A ZHANG Xiaoying, ZHOU Ziliang, YANG Weiguang, WANG Feng %T Factors Affecting the Luminescence Properties of Blue Long Afterglow Materials Doped with Eu2+ %0 Journal Article %D 2019 %J Materials Reports %R 10.11896/cldb.18060211 %P 2497-2504 %V 33 %N 15 %U {http://www.mater-rep.com/CN/abstract/article_1869.shtml} %8 2019-08-10 %X Since 1980s, four generations of blue long afterglow materials have been synthesized by doping rare earth elements into sulfides, aluminate, silicate, and light-emitting diode conversion phosphors host materials. With increasing quality of luminescent properties, blue long afterglow materials gradually meet the requirements and have been widely applied in many fields, such as display, detection, energy conversion and so on.
At present, the urgent problem that blue long afterglow materials need to be solved is to improve the lifetime and luminous intensity of the fourth generation materials, and combined with their own high luminous efficiency and high stability to meet more practical needs. Lifetime and luminous intensity have also been the focus of research for a long time. The macro factors affecting these two luminescent properties include the types and contents of alkali soil elements, doped rare earth elements, flux agents, preparation methods and conditions, etc. The emission wavelength and lifetime of the long afterglow materials are obviously changed by the first factors. The types and contents of doped rare earth elements are different in every host material. Boric acid is the most commonly used and relatively effective in the fluxes. Although the product grain is large, the high temperature solid state method is more widely used, due to its simpler process, more stable product, and better luminescent property. The pro-duct of wet chemical methods have small grain size but less product quantity, which is easy to agglomerate, the synthesis process is complex, and the synthesis time is relatively long. Although the synthesis time of combustion method, microwave synthesis method and laser synthesis method is short, but the synthesis parameters are difficult to master. In the future, the preparation of long afterglow materials may be co-doped with Eu2+ and other rare earth elements, and combined by a variety of methods in order to synthesize materials with longer life and higher intensity.
In addition to luminescent properties, the luminescence mechanism of blue long afterglow materials is also an important concern in academia. The early mechanism models of long afterglow materials includes Abbruscato model doped Eu2+ and Matsuzawa model doped Eu2+ and Dy3+, whose holes are assumed to be the main charge carriers. The Dorenbos model of rare earth ions with trap and the Clabau model of the oxygen vacancy with trap, whose electrons are the main charge carriers. The Aitasalo model of the blue long afterglow materials is integrated the trap sources of Dorenbos and Clabau et al, and the Aitasalo model is consistent with the results of H?ls? team by synchrotron radiation measurement. However, the main charge carriers are always controversial. At the same time, the above models have not described the remaining holes or electrons except the main charge carriers. Until 2017, Li et al. have proposed a luminescence mechanism model of strontium aluminate doped three rare earth elements, which not only considers the two charge carriers, electrons and holes, but also describes the two kinds of traps, intrinsic carrier and doping ions. But the model does not explain the ratio of oxygen vacancies traps to doping ions traps, and no experimental evidence about the position where the electrons or holes are captured in detail, and which traps capture them. Those facts require further data support such as electronic paramagnetic resonance and synchrotron radiation. At the same time, the clear mechanism is also helpful to guide the experiment for improvement of luminescence performance.
This paper summarizes the representative Eu2+ blue persistent luminescent materials, and analyzes the macroscopic factors affecting their luminescence properties and the generally accepted micro mechanism, in order to provide reference for the subsequent research and application of long afterglow materials.