Abstract
Anti-Stokes luminescence of up-converting nanocrystals SrF2:Yb3+,Er3+ can be used as a high pressure optical sensor alternative to the ruby fluorescence-scale. In nanocrystalline SrF2:Yb3+,Er3+, high pressure reversibly shortens the emission lifetimes nearly linearly up to 5.29 GPa at least. Its advantage is the use of NIR (≈980 nm) radiation, highly penetrable for many materials. The shortening of up-conversion lifetimes has been attributed mainly to the changes in energy transfer rates, caused by decreased interatomic distances and increased overlap integrals between 4f electrons and the valence shells of ligand ions. The origin of high-pressure effects on the luminescence intensity, band ratio and their spectral position has been explained by the increased interactions and distortions of the crystal-field symmetry around the emitting ions in the compressed structure.
Highlights
Dielectrics, semiconductors and some metals are more transparent to near infrared (NIR) light than to visible light used for the ruby excitation
Nanoscale reported for the bulk SrF2.27 The determined pressure dependence of the phonon energy values in a compression–decompression cycle is presented in Fig. S1 in the Electronic supplementary information (ESI).†
We developed a new spectroscopic method for the experimental determination of pressure based on the luminescence lifetime measurements of lanthanide ions
Summary
Functional nanomaterials are currently extensively studied due to their unique optoelectronic, magnetic and structural properties, in comparison with their bulk analogues.[1,2,3,4,5,6] This phenomenon is usually related to the large surface-to-volume ratio of the nanoparticles (NPs) and to the quantum confinement of electrons.[7,8,9,10] Luminescent NPs based on lanthanide ions (Ln3+) exhibit multicolor emission under UV or IR (upconversion) excitation, long radiative lifetimes and narrow emission bands, resulting from the 4f–4f transitions within the Ln3+ ions (forbidden by the Laporte selection rules).[11,12,13,14,15,16] Ln3+-Doped NPs are resistant to high temperature and photodegradation. Nanoscale observed a shortening of the up-conversion emission lifetimes in the compressed SrF2:Yb3+,Er3+ NPs. The strong relationship between the pressure and emission lifetimes is reversible and nearly linear.
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