Grimm J, Beurer E, Gerner P, Güdel H U
Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
Chemistry. 2007;13(4):1152-7. doi: 10.1002/chem.200600418.
Near-infrared to visible upconversion luminescence in CsCaCl3:Tm2+, CsCaBr3:Tm2+ and CsCaI3:Tm2+ is presented and analysed. The upconversion process involves exclusively the 4f-5d excited states of Tm2+, which is a novelty among upconversion materials. The presence of more than one long-lived 4f-5d excited state is the prerequisite for this. Multiple emissions from Tm2+ are observed in the title compounds. This is made possible by the favourable energy structure within the 4f-5d states and the low phonon energies of the materials. The energy positions of the relevant 4f-5d states, and thus the photophysical and light emission properties, are affected by the chemical variation along the series. The upconversion efficiency increases from chloride to iodide and the mechanism is found to be a combination of absorption and energy-transfer steps.
介绍并分析了CsCaCl3:Tm2+、CsCaBr3:Tm2+和CsCaI3:Tm2+中的近红外到可见光上转换发光。上转换过程仅涉及Tm2+的4f-5d激发态，这在发光材料中是新颖的。存在多个长寿命4f-5d激发态是其前提条件。在标题化合物中观察到了Tm2+的多重发射。这是由4f-5d态内有利的能量结构和材料的低声子能量实现的。相关4f-5d态的能量位置，进而光物理和发光特性，受到该系列化学变化的影响。上转换效率从氯化物到碘化物逐渐增加，并且发现其机制是吸收和能量转移步骤的组合。
