Zn_2SiO_4∶Mn,Cd磷光体的长余辉特性

Long-lasting Properties of Zn_2SiO_4∶Mn,Cd Phosphor

高温固相法合成Zn2SiO4∶1. 2%Mn, 5%Cd长余辉磷光体,对样品进行了X射线衍射分析、光谱分析以及余辉衰减特性测量。分析结果表明,在 1 050℃下烧结 3h的硅酸锌产物为单相。Zn2SiO4∶1. 2%Mn,5%Cd长余辉磷光体在 243nm或 260nm激发下,发射光谱最大峰值位于 521nm处,其色坐标x=0. 230 1,y=0. 691 5。在 254nm紫外光激发 5min后样品的余辉发光在暗室里可持续观察的时间约为 1h,与Zn2SiO4∶1. 2%Mn磷光体比较,显示了更好的余辉特性。

Among the host lattices for luminescent material, orthosilicate and metasilicate compounds had been extensively investigated by many researchers because of their excellent chemistry stability, visible light transparency, and relative easy preparation. For example, Mn-doped Zn_2SiO_4 phosphor which exhibits the highest emission intensity under VUV ray excitation have been intensely studied to be used for large plasma TV screens and the tricolor fluorescent lamp. In general, the phosphors doped with manganese activators have a long (decay) time according to the spin selection rule. The origin of the rather long decay time lies in the fact that the corresponding transition ()~4T_(1g)(G)→()~6A_(1g)(S) is spin forbidden. It is well known that the slow decay (lifetime) of Mn^(2+ ) is a disadvantage for the Mn^(2+) doped Zn_2SiO_4 phosphor using as the green phosphor, however, a long (lifetime) is an important requirement for the afterglow phosphor, the long lifetime of Mn^(2+) make it is feasible to be used as a activator ions in silicate host to create long-lasting phosphorescence. On the other hand, all the phosphors doped with manganese ions found up to now have short long-lasting phosphorescence, it is important to find an excellent silicate phosphor that can be applied to practical application. The aim of this work is to report on the long-lasting properties of Zn_2SiO_4∶1.2%Mn,5%Cd phosphor. XRD analysis results show that the Zn_2SiO_4∶1.2%Mn,5%Cd phosphors synthesized at 1 050 ℃ for 3 h are single phase and have no detectable amount of CdSiO_3 impurity. This phosphors show long-lasting phosphorescence under (240 nm) or (260 nm) UV light for 3 min, the afterglow light can be seen by naked eye clearly in the dark room even after the excitation source have been removed for about 1 hour. The photoluminescence spectra measurement (revealed) that under excitation of 240 and 260 nm radiation the luminescence center of Zn_2SiO_4∶1.2%Mn,5%Cd phosphors do not changed because the emission spectrum have the same peaks position and shape. The bright green emission peaks located at ～521 nm is due to the ()~4T_(1g)(G)→()~6A_(1g)(S) transition of Mn^(2+) ions. The chromaticity coordinates of this phosphor is x=0.230 1, y=0.691 5. According to the luminescence decay curves measurement results, the Zn_2SiO_4∶(1.2%Mn,)5%Cd phosphors show higher brightness compared to the Zn_2SiO_4∶1.2%Mn phosphors, we considered that the Cd^(2+) component in the Zn_2SiO_4∶1.2%Mn,5%Cd phosphor results in the longer decay time because the ionic radius of Cd^(2+) ((0.097 nm)) is relative larger than that of Zn^(2+) ((0.074 nm)) and the Cd^(2+) is easy to lost during the high temperature synthesis. By introducing 5%Cd^(2+) component to Zn_2SiO_4∶(1.2%)Mn, some electron traps or crystal defects with appropriate trap depth can be (created,) and these traps result in the long-lasting phosphorescence.