Ang Feng

VUV spectroscopic properties of rare-earth (RE=Eu, Tb and Dy)-doped A2Zr(PO4)2 (A=Li, Na and K) phosphates

Abstract This study fully investigated the vacuum ultraviolet excitation spectra of pure and rare-earth (RE=Eu, Tb and Dy)-doped A 2 Zr(PO 4 ) 2 (A=Li, Na and K) phosphors. The synthesized Na and Li compounds were characterized by XRD showing two new types of phases after indexation. Although these three pure compounds had different crystal structures, they exhibited similar luminescence properties. For Eu 3+ -activated samples, the broad excitation band centered at 217 nm could be attributed to the CT transition between O 2– ( 2 p 6 ) and Eu 3+ ions. For Tb 3+ -doped samples, two groups of f-d transitions were observed, where a strong broad band at 221 nm was due to the spin-allowed f-d transition. Energy transfer from O 2– to Dy 3+ was not observed in Dy 3+ -doped phosphors, probably because it overlapped considerably with the CT transition from O 2– to Zr 4+ at 187 nm.

Photoluminescence properties and energy levels of RE (RE = Pr, Sm, Er, Tm) in layered-CaZnOS oxysulfide

RE3+ (RE = Pr, Sm, Er, Tm)-activated CaZnOS samples were prepared by a solid-state reaction method at high temperature, and their photoluminescence properties were investigated. Doping with RE3+ (RE = Pr, Sm, Er, Tm) into layered-CaZnOS resulted in typical RE3+ (RE = Pr, Sm, Er, Tm) f-f line absorptions and emissions, as well as the charge transfer band of Sm3+ at about 3.3 eV. The energy level scheme containing the position of the 4f and 5d levels of all divalent and trivalent lanthanide ions with respect to the valence and conduction bands of CaZnOS has been constructed based on the new data presented in this work, together with the data from literature on Ce3+ and Eu2+ doping in CaZnOS. The detailed energy level scheme provides a platform for interpreting the optical spectra and could be used to comment on the valence stability of the lanthanide ions in CaZnOS.

A Review of Mechanoluminescence in Inorganic Solids: Compounds, Mechanisms, Models and Applications

Mechanoluminescence (ML) is the non-thermal emission of light as a response to mechanical stimuli on a solid material. While this phenomenon has been observed for a long time when breaking certain materials, it is now being extensively explored, especially since the discovery of non-destructive ML upon elastic deformation. A great number of materials have already been identified as mechanoluminescent, but novel ones with colour tunability and improved sensitivity are still urgently needed. The physical origin of the phenomenon, which mainly involves the release of trapped carriers at defects with the help of stress, still remains unclear. This in turn hinders a deeper research, either theoretically or application oriented. In this review paper, we have tabulated the known ML compounds according to their structure prototypes based on the connectivity of anion polyhedra, highlighting structural features, such as framework distortion, layered structure, elastic anisotropy and microstructures, which are very relevant to the ML process. We then review the various proposed mechanisms and corresponding mathematical models. We comment on their contribution to a clearer understanding of the ML phenomenon and on the derived guidelines for improving properties of ML phosphors. Proven and potential applications of ML in various fields, such as stress field sensing, light sources, and sensing electric (magnetic) fields, are summarized. Finally, we point out the challenges and future directions in this active and emerging field of luminescence research.