Mechanism of persistent luminescence in Sr₂MgSi₂O₇:Eu²⁺; Dy³⁺

Abstract

Persistent luminescence is the phenomenon that a phosphor after exposure to UV-light (day light) shows visible luminescence in the dark that persists during the whole night (≈ 10 hours). In 1996 a mechanism was proposed by Matsuzawa et al. [1] In order to develop a better mechanism it is necessary to know the location of the levels of Eu and Dy relative to the top of the valence band and the bottom of the conduction band. Recently a new method has become available to construct a scheme with the level locations for each divalent lanthanide ion in a compound with the use of few experimental parameters [4][5][6]. In this work that method is applied to Sr 2 MgSi 2 O 7 with the aim to understand the mechanism for the persistent luminescence. In a related paper the method is applied to the persistent luminescence [10] is interpreted as the threshold energy E fa = 7.15 eV for fundamental absorption. The following maximum at E ex = 7.4 eV can be interpreted as the exciton creation energy. Adding the exciton electron-hole binding energy, we estimate the bottom of the conduction band at E VC = 7.9 eV. These values are typical for silicate compounds and similar to those for Li 2 CaSiO 4 and Lu 2 Si 2 O 7 [11,12]. The value for E VC is used in Fig. 1 to draw the bottom of the conduction band relative to the top of the valence band which we define as the zero of energy.Next, information is required on the energy of charge transfer from the valence band to one of the trivalent lanthanide ions. For Eu 3+ in oxide compounds this energy is usually between 4 and 6 eV [8]. Qi et al. [3] report that ≈ 250 nm (5.0 eV) is an efficient wavelength to excite Eu 3+ emission in Sr 2 MgSi 2 O 7 . We interpret this as the energy of charge transfer (CT) to Eu 3+ . The transition as indicated by arrow 1 in Fig. 1 starts at

Enhanced luminescence performance of Sr2MgSi2O7:Eu2+ blue long persistence phosphor by co-doping with Ce3+ ions

“…These oxygen vacancies are the major contributors to the phosphorescence behavior of many oxide based phosphors. For a suitable trap depth, the trap concentration is directly depends on the cerium ions [42,43]. It is reported that a suitable trap depth (0.65-0.75 eV) is essential for phosphors to show long persistence.…”

Understanding Persistent Luminescence: Rare-Earth- and Eu2+-doped Sr2MgSi2O7

“…Nevertheless, this model can be used for the interpretation of many interesting chemical, physical and spectroscopic properties of rare-earths [74]. This model was also suggested [75] to solve the enhancement of persistent luminescence by the RE 3+ co-dopants in Sr 2 MgSi 2 O 7 :Eu 2+ . It seems now [67] that the defects due to charge compensation originating from the aliovalent substitution of Sr 2+ by RE 3+ leads to a multitude of defects overruling the rare-earth ions as traps to store the excitation energy in the charging phase of the persistent luminescence mechanism.…”

A kinetics model of red long-lasting phosphorescence in MgSiO3:Eu2+, Dy3+, Mn2+

“…However, there is a common model for the Eu 2+ and Dy 3+ co-doped long-lasting phosphors that suggests the Dy 3+ ions as hole-trapped to form Dy 4+ , which has been doubted by several researchers [13,14]. In contrast, our suggestion is more reasonable.…”

“…It has been suggested that Dy 3+ ions act as trap centers in many long-lasting phosphors doped with Eu 2+ and Dy 3+ [13]. Thus we consider that the function of Dy 3+ ions is the same in MgSiO 3 :Eu 2+ , Dy 3+ , Mn 2+ .…”