Luminescent Nanocrystals


Times Beacon Record Article

Prof. Dickerson has been featured in a recent article, entitled BNL's James Dickerson: facilitating nanotechnology.  Check it out!

Read Article

7

Prof. Dickerson just recently Guest Edited the Journal of the Electrochemical Society’s Focus Issue on Electrophoretic Deposition (http://jes.ecsdl.org/content/162/11.toc).  This collection of articles on EPD features many of the cutting-edge trends in the field.

Read Article

Monolayer Ticker

A new article on nanoparticle monolayer formation, led by Alex Krejci, was published in ACS Applied Materials and Interfaces.

Read Article

9

Shalom and Jyotishka have had their manuscript on electrochemical separation of carbon nanotube films published by the Journal of the Electrochemical Society. Congratulations Jyotishka and Shalom!

Read Article

8

Our article on iron oxide nanoparticle monolayer formation by electrophoretic deposition was published by ACS Materials and Interfaces.

Read Article

1

Hardcover versions of Electrophoretic Deposition of Nanomaterials can be accessed via the 'Read Article' link below.

Read Article

2

The Spring 2012 MRS Conference was a great success.  Prof. Dickerson presented an Invited Talk on our Rare Earth Nanoparticles.  He also will be the Editor of the YY:Rare-Earth-Materials Section of the MRS Conference Proceedings.

Read Article

3

Article on graphene oxide films published in ACS Nano.

Read Article

4

Weidong He has finished his PhD with us. Congratulations, Weidong, and best of luck at Pacific Northwest National Laboratory!

Read Article

5

Dr. Suseela Somarajan successfully defends her PhD dissertation. Congratulations Suseela!

6

Prof. Dickerson is awarded a National Science Foundation CAREER Award!

Read Article

Synopsis:

We have investigated lanthanide (also known as rare earth (RE) nanocrystals, such as europium oxide (Eu2O3), terbium oxide (Tb2O3), and lanthanide doped-gadolinium oxide (Gd2O3: RE3+), for their robust optical properties.  Their high luminescence intensity, chromaticity, small feature size, and long luminescence lifetimes make these nanomaterials attractive candidates for applications, such as high-resolution video displays, solid state lighting, and medical imaging.

Major Achievements:

Observed size-dependent luminescence that is not due to quantum confinement effects.  A portion of this research is the subject of a patent application.

Detailed Discussion:

Luminescent nanocrystals have attracted significant research attention recently for their potential use in industrial and commercial imaging and lighting applications due to quantum confinement and other low-dimensional, size-dependent effects.  Innovations, from biocompatible imaging reagents to thin film electroluminescent displays and solid state lighting, provide motivation for the research.  Our work in this area resides in how the physical properties of phosphorescent materials (materials that possess exceptionally long light emission lifetimes) are altered when the size of the materials is reduced to the nanoscale.  The lanthanide sesquioxides (RE2O3) provide ideal systems to study nanoscale optical properties (absorption, luminescence, excitation energy transfer, etc.) because these materials are f-block compounds, similar to the europium chalcogenides discussed in the magnetic nanoparticle section.  The f-block nature of these materials is important because the interaction between neighboring lanthanide ions is substantial enough in the bulk RE2O3 crystals to give rise to concentration quenching, which is one of the primary cause of light emission losses (i.e. diminished efficiency) in lanthanide phosphors..  Concentration quenching arises from excitation energy transfer between nearest neighbor lattice sites and next-nearest neighbor sites.

Bulk lanthanide-based materials have been used extensively as visible light phosphors in a variety of devices, such as cathode-ray tube monitors, field emission systems, electroluminescent displays, and dopants to enhance the luminescent properties of their host materials. interestingly, for most lanthanide nanocrystals, specific concern about the size of the material is largely irrelevant.  This is because the optical properties of rare-earths are due to ionic transitions.  For example, the 5DJ7F transition of the Eu3+ ion in europium sesquioxide (Eu2O3) typically are not influenced by the size of the nanomaterial, that is, confinement effects on the magnetic and electronic dipole transitions generally are not observed. Most research on these materials has sought improved light emission efficiency by surveying which rare-earth ion or which host materials optimized the luminescence.  We contend that other size-dependent phenomena, such as strain induced from a reduced surface-to-volume ratio, may give rise to marked enhancements in the optical properties.  This led us to investigate Eu2O3, Tb2O3, and Gd2O3:RE3+ (RE = Eu, Tb) nanophosphors, synthesized in a range of sizes, down to 1.8 nm in diameter, as test cases to investigate the correlation among Optical Effects (efficiency due to concentration quenching) and Size-Dependent Effects.  This investigation focused on two colors that are integral to the video display industry: Red (Eu2O3 and Gd2O3:Eu3+) and Green (Tb2O3 and Gd2O3:Tb3+).  The belief was that we would discover a size regime for which the luminescence efficiency of europium or terbium sesquioxide nanostructures will be comparable, if not larger, than the efficiency obtained for commercial phosphors in which europium and/or terbium are doped into a typical phosphor host environment.

Slide 2illustrates a typical Gd2O3:Eu3+ NC, synthesized by my research group for this study.  Of substantial interest is the emergence of a new luminescence peak at 620 nm, a characteristic which had not been reported in other Eu3+-based lanthanide sesquioxide nanostructures.  The photoluminescence spectra were recorded for the Eu2O3 and Gd2O3:Eu3+ nanocrystals of different sizes.  We attribute the peaks at 612 nm, 620 nm, and 625 nm to the 5D07F2 transition of Eu2O3 and Gd2O3:Eu3+ nanocrystals.  The observed peak broadening for our nanocrystals is consistent with that observed for the other nanocrystalline Eu2O3 and Gd2O3:Eu3+ materials.  Comparing the spectra of our nanocrystals with the spectra reported for nanocrystalline and bulk Eu2O3 materials, we easily identify the conventional peak for cubic Eu2O3 at 612 nm.  The peak at 625 nm has been reported for cubic Eu2O3 nanodisks, which the authors explained as due to the occupation of Eu3+ ions in a unique site due to ultrathin thickness (1.6 nm) of nanodisks.  The presence of this spectral feature suggests a similar size-dependent effect on the 7FJ states in our nanocrystals.

Reference Articles:

a. S.V. Mahajan and J.H. Dickerson, Understanding the growth of Eu2O3 nanocrystal films made via electrophoretic deposition, Nanotechnology 21, 145704, 2010.
b. S.V. Mahajan and J.H. Dickerson, Optical studies of sub-3nm Eu2O3 and Gd2O3:Eu3+ nanocrystals, Journal of Alloys and Compounds 488, 574, 2009.
c. S. V. Mahajan, J. Hart, J. Hood, A. Everheart, M. L. Redigolo, D. S. Koktysh, E. A. Payzant, and J. H. Dickerson, Synthesis of RE(OH)2Cl and REOCl (RE = Eu, Tb) nanostructures, J. Rare Earths 26 (2), 131, 2008.
d. S. V. Mahajan and J. H. Dickerson, Synthesis of monodisperse sub-3 nm RE2O3 and Gd2O3:RE3+ nanocrystals, Nanotechnology 18, 325605, 2007.


© Copyright 2017 by James H. Dickerson II.

Be the best that you can be!