Crystal structure and optical properties of erbium- and neodymium-doped zirconia nanoparticles
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Dajie Zhang The Johns Hopkins University, Advanced Technology Laboratory, Baltimore, Maryland 20723
Lisa Kelly The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723; and University of Maryland, Baltimore, Maryland 21201
Jennifer Sample The Johns Hopkins University, Applied Physics Laboratory, Laurel, Maryland 20723 (Received 17 September 2009; accepted 24 November 2009)
We report the synthesis, characterization, and optical properties of high-temperature stable lanthanide-doped luminescent zirconia nanoparticles via a novel method using carbon black as template. Dopant concentrations were varied from 1 to 5% of Er3+ or Nd3+ and annealing temperatures were varied from 650 to 1100 C. The effects of the dopant concentration on crystal structure and emission properties were evaluated using x-ray powder diffraction and fluorescence spectroscopy, respectively. The lanthanide cations were found to stabilize the tetragonal phase of zirconia over the monoclinic phase as dopant concentration was increased to 5%. Increasing the annealing temperature to 1100 C had the opposite effect and was found to stabilize the monoclinic phase of zirconia. The luminescence intensity of the Nd-doped zirconia was enhanced by two orders of magnitude over the undoped or Er-doped zirconia. In all cases, the luminescence spectra revealed increasing intensity with increasing annealing temperature. Zirconia luminescence at near-infrared wavelengths is likely caused by oxygen vacancies. This work demonstrates that the spectral signatures of fluorescent zirconia nanoparticles can be modified with small lanthanide dopant concentration. These particles will have utility in fluorescent sensors and tags, as well as new in refractory materials.
I. INTRODUCTION
Nanoparticles that fluoresce or absorb light in the visible and near-IR wavelengths are desirable for a variety of applications that include optical waveguides,1 phosphors for display devices,2 and biological tagging for medical imaging purposes.3 It is well known that lanthanide cations are photoluminescent because of their abundance of 4f–4f and 4f–5d transitions.4 The fabrication and structure–property relationships of nanoscale lanthanide phosphors and lanthanide-doped nanocomposites and nanoparticles have been extensively studied.5–8 These lanthanide phosphors can exist in many forms within the host matrix including chelated molecular complexes, halides, and oxides. The host matrix materials include fluoride and oxyfluoride optical glasses, such as NaYF,9 SiO2–Al2O3–NaF–YF3,10 and oxide glass/ ceramics including SiO2,11 ZrO2,12 Y2O3,13 Y3Al5O12 a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0071
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http://journals.cambridge.org
J. Mater. Res., Vol. 25, No. 3, Mar 2010 Downloaded: 13 Jun 2014
(yttrium aluminum garnet; YAG).14 They are generally optically transparent, especially in the infrared (IR) spectral region. Zirconia is a technologically important material due to its large refractive index a
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