Persistent luminescence

Cathode ray tube phosphors with fast luminescence as well as persistent luminescence are needed in different situations. A variety of phosphors of the ZnS-CdS family are used for the purpose with Ag, Cu etc. as dopants. Other host lattices used are CaS, Zu2Si04, Y2O2S and Zn3(P04)2 typical dopants are Mn, Ce, Eu and Tb. 

It seems attractive to use luminescence properties of AIN ceramics for practical application. Though not yet implemented finally, there are several areas of experimental studies aimed at getting developments into actual practical use, such as dosimetry, persistent luminescence, lasing (in the case of translucent ceramics), and others. Some of them will be briefly considered here. 

Fig. 6.19 The schematic persistent luminescence of CaAlOsiEu -", Nd -" phosphors based on the DFT calculation. Adapted from Ref. [73] by permission of American Chemical Society...

Qu BY, Zhang B, Wang L, Zhou RL, Zeng XZ (2015) Mechanistic study of the persistent luminescence of CaAl204 Eu,Nd. Chem Mater 27 2195... 

As discussed previously, Eu -doped Ms(P04)3X (M = Ca, Sr, Ba X = F, Cl, Br) phosphors generally show efircient blue emission, which can he used in tricolor fluorescent lamps and LEDs [53]. Except for this, it was interestingly found that Ba5(P04)3Cl Eu and Ba5(P04)3Cl Eu % Ce " can be used as long-persistent phosphors, but their afterglow intensity is very weak. The persistent luminescence of Ba5(P04)3Cl Eu, was enhanced with co-dopants La ", Ce ", Gd, Tb -", and Lu ... 

Moreover, long-persistent luminescence (LPL) phosphors can be also found in such a Sr3Al205Cl2system [94-96]. A novel orange-yellow-emitting Sr3Al205Cl2 LPL phosphor has been recently developed. The incorporation of Tm " ... 

Dutczak D, Ronda C, Meijraink A, Jirstel T (2013) Red luminescence and persistent luminescence of Sr3Al205a2diu, Dy. J Lumin 141 150... 

Table 16.9 Other long persistent luminescent phosphors...

The transfer-of-positive-hole mod was first suggested by Matsuzawa et al. to explain the extraordinary persistent luminescence of SrAl204 Eu , Dy ", so this model is also called the Matsuzawa model. In this model, the investigators explained the persistent luminescence using the theory of luminescence in semiconductors, i.e., they mainly analyzed the captured electrons and holes, the local level caused by the impurity ions, and the energy transfer between the conduction bands and the valence bands. A schematic picture of the transfer-of-... 

The energy-level depth of the doping ions decides the persistence time and the emission intensity. When the depth is low, the ions rapidly release the holes and do not actively take part in persistent emission processes at room temperature. When the depth is deeper, more energy is required, and the ions slowly release the holes. Therefore, to observe persistent luminescence at room temperature, the depth should have appropriate activation energy somewhere between these two extremes. The hole in the valence bands has been confirmed by experiments, but the transfer-of-positive-hole mode has not been accepted completely. The main question is whether or not the Eu" ion exists. It is well known that the trivalent ion of lanthanide is stable and that the tetravalence ion of lanthanide is hard to form under visible-light excitation. There is no evidence to indicate that Eu", Er, Ho" ", Dy" " ions exist in the host lattice. 

Aitasalo T, Holsa J, Kirm M, Laamanen T, Lastusaari M, Niittykoski J, Raud J, Valtonen R (2007) Persistent luminescence and synchrotron radiation study of the Ca2MgSi207 Eu R3 + materials. Radiat Meas 42 644-647... 

Aitasalo T, Holsa J, Jungner H, Lasmsaari M, Niittykoski J (2001) Mechanisms of persistent luminescence in Eu, RE " doped alkaline earth aluminates. J Lumin 94—95 59-63... 

---