Wydział Chemii

Patric Lindqvist-Reis

Florent Réal

Rafał Janicki

Valérie Vallet

2018

Inorganic Chemistry

57

10111-10121

10.1021/acs.inorgchem.8b01224

Naukowa

Angielski

Artykuł

The 4f-5d transition of Ce³⁺ provides favorable optical spectroscopic properties such as high sensitivity and quantum yield, making it a most important dopant for lanthanide-activated phosphors. A key for the design of these materials with fine-tuned color emission is a fundamental understanding of the Ce³⁺ ground state and excited state structures and the dynamics of energy transfer. Such data is also crucial for deriving coordination chemistry information on Ce³⁺ ions in different chemical environments directly from their optical spectra. Here, by combining 4f-5d absorption and luminescence spectroscopy and highly accurate quantum chemical electronic structure calculations, we study the interplay between the local structure of Ce³⁺ in aqueous solutions and in crystalline hydrates, the strengths of Ce–O/Cl interactions with aqua and chloride ligands, and the resulting absorption and luminescence spectra. Experimental and theoretical absorption spectra of [Ce(H₂O)₉]³⁺ and [Ce(H₂O)₈]³⁺ with defined geometries provide a means for analyzing the equilibrium between these species in aqueous solution as a function of temperature (K(298) = 0.20 ± 0.03), while analyses of spectra of different aqua-chloro complexes reveal that eight-coordinate aqua-chloro complexes are present in solution at high chloride concentration. An intriguing feature in these systems concerns the large observed Stokes shifts, 5500–10 100 cm^–1. By exploring the excited state potential energy surfaces with relativistic multireference calculations, we show that these shifts result from significant geometrical relaxation processes in the lowest 5d¹ excited state. For [*Ce(H₂O)₈]³⁺ the relaxation gives shorter Ce–O bonds and a Stokes shift of ∼5500 cm^–1, while for [*Ce(H₂O)₉]³⁺ the lowest 5d¹ state results in a spontaneous dissociation of a water molecule and a Stokes shift of ∼10 100 cm^–1. These findings are important for the understanding and optimization of luminescence properties of cerium complexes.

http://dx.doi.org/10.1021/acs.inorgchem.8b01224

https://www.acs.org/content/acs/en.html