ZnS:Eu2+的长余辉发光

Eu2+的5d能级在许多晶体中都低于其4f能级的最低激发态(6P7/2),因此发光呈带状光谱,且发射波长随基质变化很大。由于5L→4f是容许跃迁,所以发光的衰减很快,通常在μs数量级,出人意料的是ZnS:Eu的发光尽管也是Eu2+的5d→4f跃迁,但衰减却极慢,达几十分钟的数量级。弛豫曲线的分析表明,这种长的弛豫是电子陷阱造成的。

LONG PERSISTENT LUMINESCENCE OF ZnS:Eu2+

An abnormal property of luminescence of ZnS:Eu2+ is reported.The excitation and emission spectra of ZnS:Eu2+ are shown in Fig.1. Both are wide bands peaking at 400 nm and 550 nm respectively. This indicates that the luminescence is due to f-d transition of Eu2+.The afterglow of the yellow emission was measured.It was surprising to observe that the decay turns out to be tens of minutes long and follow a power law I?t-n with n=1.24 (Fig.2).Since f-d transition is an allowed one, the luminescence corresponding to it should have a very short lifetime, e. g. 1us. So it is believed that this long persistent afterglow must be due to the existence of some kind of electron traps, the origin and the nature of which are to be clarified.