Related Experiment Video
Updated: Jul 19, 2026

Integrating a Triplet-triplet Annihilation Up-conversion System to Enhance Dye-sensitized Solar Cell Response to Sub-bandgap Light
Published on: September 12, 2014
Upconversion Between 4f-5d Excited States in Tm2+-Doped CsCaCl3, CsCaBr3, and CsCaI3
1Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, 3012 Bern, Switzerland.
Abstract:
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.
Related Concept Videos
Photochemical Electrocyclic Reactions: Stereochemistry
Selection Rules: Photochemical Activation
Deactivation Processes: Jablonski Diagram
¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
Hybridization of Atomic Orbitals II
Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
UV–Vis Spectroscopy: Molecular Electronic Transitions

