Multicolor upconversion luminescence of GdVO4:Ln3þ/Yb3þ (Ln3þ ¼ Ho3þ, Er3þ, Tm3þ, Ho3þ/Er3þ/Tm3þ) nanorods

Tamara V. Gavrilovic , Dragana J. Jovanovic,  Krisjanis Smits, Miroslav D. Dramicanin 

Lanthanide-doped GdVO4 nanorods that exhibit upconversion emission under 982 nm excitation have
been prepared by a facile room-temperature chemical co-precipitation method followed by a subsequent
annealing at temperatures of 600 C, 800 C and 1000 C. Multicolor upconversion emission, including
white, was achieved by tuning the concentrations of dopant lanthanide ions (Ho3þ, Er3þ, Tm3þ and Yb3þ)
in GdVO4. It is found that four GdVO4 samples emit light with the white chromaticity coordinates of
(0.326, 0.339), (0.346, 0.343), (0.323, 0.327) and (0.342, 0.340) respectively, under a single-wavelength
NIR excitation. These coordinates are very close to the standard equal energy white light coordinates
(0.333, 0.333) according to the 1931 CIE diagram. By varying dopant lanthanide concentrations in
nanorods it is possible to produce upconversion emission with colors between red (0.504, 0.369), green
(0.282, 0.577) and blue (0.142, 0.125) coordinates.

Dyes and Pigments 126 (2016) 1e7

doi:10.1016/j.dyepig.2015.11.005

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Luminescence properties of zirconia nanocrystals prepared by solar physical vapor deposition

Krisjanis Smits , Larisa Grigorjeva , Donats Millers , Karlis Kundzins , Reinis Ignatans , Janis Grabis , Claude Monty

Zirconia nanocrystals have attracted considerable interest as biolabels, which can be used as probes for
medical imaging and biosensor applications. However, zirconia particle agglomeration forms amajor limitation
to its use for biolabeling. In this backdrop, for the first time, well-separated zirconia nanocrystals
were obtained in a Heliotron reactor (PROMES CNRS, France) via the solar physical vapor deposition
(SPVD) method. As the raw material target for solar evaporation, zirconia nanopowders obtained via
the sol–gel process were used. The luminescence and upconversion luminescence properties of the Sol
Gel nanopowders were compared with those of the SPVD nanocrystals. Erbium was chosen as the luminescence
center with ytterbium as the sensitizer, and along with these two dopants, niobium was also
used. Niobium acts as a charge compensator to compensate for depletion in the charge due to the
introduction of trivalent erbium and ytterbium at tetravalent zirconium sites. Consequently, the
oxygen-vacancy concentration is reduced, and this results in a significant increase in the upconversion
luminescence.
The SPVD-prepared samples showed less agglomeration and a fine crystal structure as well as high
luminescence, and thus, such samples can be of great interest for biolabeling applications.

Optical Materials 37 (2014) 251–256

http://dx.doi.org/10.1016/j.optmat.2014.06.003

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The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

K. Smits, A. Sarakovskis, L. Grigorjeva, D. Millers, and J. Grabis

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity
in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb
co-doping were prepared by sol-gel method and thermally annealed to check for the impact of
phase transition on luminescence properties. Phase composition and grain sizes were examined by
X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission
electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison
of samples with different oxygen vacancy concentrations and different Nb concentrations
confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic
phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they
also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain
surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion
luminescence intensity. Hence, ZrO2:Er:Yb:Nb nanocrystals may show promise for upconversion
applications

Journal of Applied Physics 115, 213520 (2014)

DOI:10.1063/1.4882262

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The role of Nb in intensity increase of Er ion upconversion luminescence in zirconia

K. Smits, A. Sarakovskis, L. Grigorjeva, D. Millers, J. Grabis

It is found that Nb co-doping increases the luminescence and upconversion luminescence intensity
in rare earth doped zirconia. Er and Yb-doped nanocrystalline samples with or without Nb
co-doping were prepared by sol-gel method and thermally annealed to check for the impact of
phase transition on luminescence properties. Phase composition and grain sizes were examined by
X-ray diffraction; the morphology was checked by scanning- and high-resolution transmission
electron microscopes. Both steady-state and time-resolved luminescence were studied. Comparison
of samples with different oxygen vacancy concentrations and different Nb concentrations
confirmed the known assumption that oxygen vacancies are the main agents for tetragonal or cubic
phase stabilization. The oxygen vacancies quench the upconversion luminescence; however, they
also prevent agglomeration of rare-earth ions and/or displacement of rare-earth ions to grain
surfaces. It is found that co-doping with Nb ions significantly (>20 times) increases upconversion
luminescence intensity. Hence, ZrO2:Er:Yb:Nb nanocrystals may show promise for upconversion
applications.

VC 2014 AIP Publishing LLC.

doi: 10.1063/1.4882262

http://dx.doi.org/10.1063/1.4882262

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