Energy transfer and photoluminescence properties of lanthanide-containing polyoxotitanate cages coordinated by salicylate ligands

Li, N; Wright, DS; Reisner, E; Luo, H-K; Matthews, P; Xiao, J; Chellappan, V; Subramanian, GS; Rosser, TE

Abstract

Polyoxotitanate (POT) cages have attracted considerable attention recently; much of this from the fact that they can be considered to be structural models for the technologically important semiconductor TiO2. Among the reported POT cages, lanthanide-containing (Ln-POT) cages are of particular interest owing to the fascinating luminescence properties of Ln(3+) ions and the versatile coordination environments that they can adopt. In the present study, we report the energy transfer mechanism and photoluminescence properties of a series of isostructural Ln-POT cages coordinated by salicylate ligands, of general formula [LnTi(6)O(3)((OPr)-Pr-i)(9)(salicylate)(6)] (Ln-1, Ln = La to Er excluding Pm). Both visible (for Pr-1, Sm-1, Eu-1, Ho-1 and Er-1) and near-infrared (for Nd-1 and Er-1) Ln(3+)-centred photoluminescence can be sensitised in solution, and most importantly, their excitation bands all extend well into the visible region up to 475 nm. With the assistance of steady-state and time-resolved photoluminescence spectroscopy, an energy-transfer mechanism involving the salicylate-to-Ti4+ charge-transfer state is proposed to account for the largely red-shifted excitation wavelengths of these Ln-1 cages. The photoluminescence quantum yield of Nd-1 upon excitation via the charge-transfer state reaches 0.30 +/- 0.01% in solution, making it among the highest reported values for Nd3+-complexes in the literature.

Citation

Li, N., Wright, D., Reisner, E., Luo, H., Matthews, P., Xiao, J., …Rosser, T. (2018). Energy transfer and photoluminescence properties of lanthanide-containing polyoxotitanate cages coordinated by salicylate ligands. Dalton Transactions, 5679-5686. https://doi.org/10.1039/C8DT00825F

• Acceptance Date: Mar 29, 2018
• Publication Date: Apr 28, 2018
• Journal: Dalton Transactions
• Print ISSN: 1477-9226
• Publisher: Royal Society of Chemistry
• Pages: 5679-5686
• DOI: https://doi.org/10.1039/C8DT00825F
• Publisher URL: http://dx.doi.org/10.1039/c8dt00825f