Abstract

TOWNSEND, P.D.; YANG, B  and  WANG, Y. Luminescence detection of phase transitions in crystals and nanoparticle inclusions. Rev. mex. fis. [online]. 2008, vol.54, suppl.2, pp.21-28. ISSN 0035-001X.

Luminescence measurements are extremely sensitive to variations in structural environment and thus have the potential to probe distortions of fluorescence sites. Changes can be monitored via luminescence efficiency, emission spectra or excited state lifetimes and these factors are influenced by the local neighbourhood around the emission site, and therefore by structure, composition, pressure and temperature. A rarely exploited approach for condensed matter has been to use the changes in luminescence responses during heating or cooling of a material to provide a rapid survey to detect the presence of phase transitions. One can often differentiate between bulk and surface effects by contrasting results from radioluminescence for bulk responses, and cathodoluminescence or photoluminescence for surface effects. One expects that discontinuous changes in optical parameters occur during temperature changes through phase transitions of insulating materials. In practice, optical signals also exist from surface states of fullerenes and high temperature superconductors etc which identify the presence of structural or superconducting transitions. Numerous examples are cited which match standard documented transitions. Interestingly, many examples show the host signals are strongly sensitive to impurity phase transitions from inclusions such as nanoparticles of water, N₂, O₂ or CO₂. Recent luminescence data reveal many examples of new transitions, hysteresis and irreversible changes. The signals equally respond to relaxations of a structure and surprisingly indicate that in some materials, such as SrTiO₃ or ZnO, ion implantation of the surface triggers relaxations and phase changes throughout the bulk of the material. Luminescence routes to detect phase transitions are powerful tools but have a tiny literature and so the subject is ideal for rapid exploitation and development.

Keywords : Phase transitions; nanoparticle inclusions; luminescence.

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