skip to main content


Title: Femtosecond Measurements Of Size-Dependent Spin Crossover In FeII(pyz)Pt(CN)4 Nanocrystals

We report a femtosecond time-resolved spectroscopic study of size-dependent dynamics in nanocrystals (NCs) of Fe(pyz)Pt(CN) 4. We observe that smaller NCs (123 or 78 nm cross section and < 25 nm thickness) exhibit signatures of spin crossover (SCO) with time constants of ~ 5-10 ps whereas larger NCs with 375 nm cross section and 43 nm thickness exhibit a weaker SCO signature accompanied by strong spectral shifting on a ~20 ps time scale. For the small NCs, the fast dynamics appear to result from thermal promotion of residual low-spin states to high-spin states following nonradiative decay, and the size dependence is postulated to arise from differing high-spin vs low-spin fractions in domains residing in strained surface regions. The SCO is less efficient in larger NCs owing to their larger size and hence lower residual LS/HS fractions. Our results suggest that size-dependent dynamics can be controlled by tuning surface energy in NCs with dimensions below ~25 nm for use in energy harvesting, spin switching, and other applications.
 [1] ;  [2] ;  [1] ;  [3] ;  [2] ;  [2] ;  [4]
  1. Univ. of Colorado, Boulder, CO (United States). JILA
  2. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  3. National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
  4. Univ. of Colorado, Boulder, CO (United States). JILA and Dept. of Chemistry and Biochemistry
Publication Date:
Report Number(s):
Journal ID: ISSN 1948-7185
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry Letters
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 1948-7185
American Chemical Society
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
14 SOLAR ENERGY; 77 NANOSCIENCE AND NANOTECHNOLOGY; femtosecond; spin-crossover; nanocrystals; time-resolved spectroscopy; high spin; low spin; transient absorption
OSTI Identifier: