Article pubs.acs.org/IC
Superlong and Color-Tunable Red Persistent Luminescence and Photostimulated Luminescence Properties of NaCa2GeO4F:Mn2+,Yb3+ Phosphor Zhenbin Wang, Wenxiang Wang, Hui Zhou, Jiachi Zhang,* Shanglong Peng,* Zhengyan Zhao, and Yuhua Wang Key Laboratory for Magnetism Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000, People’s Republic of China S Supporting Information *
ABSTRACT: An excellent persistent luminescence (PersL) phosphor NaCa2GeO4F:Mn2+,Yb3+ has been synthesized by traditional solid-state reaction. By controlling the occupation sites of Mn2+ emitters, the PersL color of this phosphor can be optionally tuned in the red to green-yellow region, and the maximum spectral shift is more than 50 nm. Significantly, the red PersL can be measured for approximately 13 and 3 h (0.32 mcd/m2) and can be observed for more than 20 and 5 h with darkadapted vision after exposure to ultraviolet irradiation and artificial sunlight, respectively. The crystal/electronic structure and photoluminescence/PersL properties of this phosphor have been investigated in detail. A series of the excitation temperaturedependent thermoluminescence experiments and the initial rising method have been conducted to study the trap properties of this phosphor. It reveals the reasons for the variation of PersL color, excellent red PersL, and degradation of green-yellow PersL. According to the results, the as-prepared NaCa2GeO4F:Mn2+,Yb3+ can be considered as an excellent red PersL phosphor, and it also has potential for application in optical storage.
1. INTRODUCTION
commercialized and are being widely used because of their sufficiently strong and long PersL. Unfortunately, the PersL duration time of the red Y2O2S:Eu3+,Ti4+,Mg2+ is not sufficiently long for practical applications. In addition, the oxysulfide host is unstable and sensitive to moisture, and in particular, the sulfurization agent is harmful to the environment.16 Therefore, the present red PersL phosphors are far away from the desired requirements. In addition, it is generally expected to obtain white PersL and even any other color by mixing tricolor PersL phosphors. However, because of the lack of the excellent red PersL phosphor, it is very difficult to obtain stable white PersL.17 Consequently, there is a strong demand ongoing for developing excellent red PersL phosphors at present.
Persistent luminescence (PersL) phosphors can store the excitation energy by absorbing ultraviolet or visible lights and then release the energy gradually for a quite long time from a few seconds to several hours by means of visible light after removal of the excitation source at room temperature.1−4 This phenomenon is due to thermally stimulated recombination of charge carriers (electrons and/or holes) and has attracted considerable attention in recent years.5−7 Such phosphors are being widely used as night-vision materials in various important fields, for example, security signs, emergency route signs, traffic signage, decorations, displays, energy, and in vivo bioimaging.8−12 To date, the primary tricolor PersL phosphors generally include green (SrAl2O4:Eu2+,Dy3+, >30 h),13,14 blue (CaAl2O4:Eu2+,Nd3+, >10 h),6 and red (Y2O2S:Eu3+,Mg2+,Ti4+,
