Abstract:Based on the Kronig–Penney model, the changing tendency of the bandgap or of a particular level with the volume deformation in crystalline materials has been derived. On the basis of this changing tendency, the zero-phonon charge transfer (CT) energy is deduced to be decreased when the size of Y2O3:Eu3+ phosphor decreases into the nanoscale. In addition, the rigidity decrease of the lattice environment in Y2O3:Eu3+ nanophosphor leads to the enlargement of the CT state coordinate offset of the optical centers; … Show more
“…We presented the detailed discussion about parameters influencing the exact CT position in our previous work (Banski et al 2010). Moreover, the observed position of absorption band is in a good agreement with the literature values equal to 240–255 nm for Y 2 O 3 :Eu 3+ (Shang et al 2011). Fig.…”
We examined in detail the optical properties of NaYF4:Eu3+ nanocrystals of ~9 nm in diameter. For such small nanocrystals roughly 17 % of Y3+ ions occupy surface sites and can be efficiently substituted by optically active Eu3+ ions. In order to determine the influence of surface Eu3+ on the optical properties of the whole nanocrystal, small β-NaYF4:Eu3+ nanocrystals with homogenous size distribution were prepared using trioctylphosphine oxide as a coordinating solvent. In order to passivate the surface sites, a thin β-NaYF4 shell was further deposited on nanocrystals core and the optical properties were investigated. For this purpose absorption, photoluminescence, photoluminescence excitation, and photoluminescence decays were recorded and analyzed. The optical characteristics of surface Eu3+ significantly diminish for surface passivated nanocrystals. We calculated the increase of quantum yield to the value of 64 % when NaYF4:Eu3+ core was capped by undoped shell. The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio.
“…We presented the detailed discussion about parameters influencing the exact CT position in our previous work (Banski et al 2010). Moreover, the observed position of absorption band is in a good agreement with the literature values equal to 240–255 nm for Y 2 O 3 :Eu 3+ (Shang et al 2011). Fig.…”
We examined in detail the optical properties of NaYF4:Eu3+ nanocrystals of ~9 nm in diameter. For such small nanocrystals roughly 17 % of Y3+ ions occupy surface sites and can be efficiently substituted by optically active Eu3+ ions. In order to determine the influence of surface Eu3+ on the optical properties of the whole nanocrystal, small β-NaYF4:Eu3+ nanocrystals with homogenous size distribution were prepared using trioctylphosphine oxide as a coordinating solvent. In order to passivate the surface sites, a thin β-NaYF4 shell was further deposited on nanocrystals core and the optical properties were investigated. For this purpose absorption, photoluminescence, photoluminescence excitation, and photoluminescence decays were recorded and analyzed. The optical characteristics of surface Eu3+ significantly diminish for surface passivated nanocrystals. We calculated the increase of quantum yield to the value of 64 % when NaYF4:Eu3+ core was capped by undoped shell. The optical spectroscopy techniques were shown to be sufficient in determination of surface passivation of nanocrystals with high surface to volume ratio.
“…However, the increasing effect of the polarizability of the cation by inserting more and more Eu 3+ in the lattice might well lead to a deviation from linearity as shown by the E CT -curve. The JR-2 line in Fig 9 suggests 9 According to these authors the change of the bandgap energy E g can be written as:…”
Section: Figsmentioning
confidence: 99%
“…Jia et al 8 measured a redshift of the E CT of 6 nm upon particle size reduction from 2-3 μm to 7 nm. Shang et al 9 and Zhang et al 10 reported large red shifts, 11 nm and 7 nm, in reducing the size of Y 2 O 3 :Eu 3+ nanoparticles from 40 nm to 9 nm and from 40 nm to 5 nm respectively. Semiconductor particles are expected to show a blueshift of their absorption peaks in reducing the particle size from 15 to 5 nm because of quantum confinement.…”
mentioning
confidence: 99%
“…1 The wavelength of the maximum of the CT-band in Y 2 O 3 :Eu 3+ , indicated by the E CT in this study and expressed in nanometers (nm) or electron-volts (eV) depends on the concentration of the Eu 3+ dopant and the size of the phosphor particles. [2][3][4][5][6][7][8][9][10] Upon increasing the Eu 3+ concentration between 1 and 15 Mol % a redshift of the E CT of about 6 nm has been observed, [2][3][4] whereas Kang et al 5 did not observe a change of E CT in increasing the Eu 3+ dope from 2 to 10 Mol %. Some peculiar observations were reported on the effect of the particle size of Y 2 O 3 :Eu 3+ .…”
In this article we describe the redshift of the charge transfer band of nanosized cubic (Y 1−x Eu x ) 2 O 3 upon increasing the Eu 3+ concentration. This redshift amounts to 0.43 eV (25 nm) in going from 0.1 Mol % Eu 3+ to 100 Mol % (which is pure Eu 2 O 3 ). The charge transfer band consists of two broad sub-bands; both shift almost parallel with the Eu 3+ concentration and are related to the two symmetry sites for the cation, C 2 and C 3i , in the bixbyite-type lattice. The area ratio of the bands is 3:1 and is the first direct evidence for the population of the two lattice sites by the Eu 3+ cations being in accord with the crystal structure ratio. A model is presented that quantitatively describes the redshift of the charge transfer band of (Y The red luminescent phosphor Y 2 O 3 :Eu 3+ has been studied extensively, because of its rather high efficiency and high stability to electron bombardment, UV-irradiation and ion bombardment. These attributes led cubic Y 2 O 3 :Eu 3+ to be widely employed in cathode ray tubes (projection tubes) and it is still used in fluorescent lamps. Many properties of this phosphor have been studied by photoluminescence (PL) and cathodoluminescence (CL) spectrometry and have been well documented, because of its industrial applications. Notwithstanding the extensive literature on Y 2 O 3 :Eu 3+ , voids still exist in our knowledge on this phosphor. One of these voids is related to the position of the charge transfer (CT) band in the excitation spectrum, although this subject has been widely studied. In the present study we shall focus on the position of the CT-band, which is located at 253 nm in Y 2 O 3 when doped with 0.1 Mol % Eu 3+ . 1 The wavelength of the maximum of the CT-band in Y 2 O 3 :Eu 3+ , indicated by the E CT in this study and expressed in nanometers (nm) or electron-volts (eV) depends on the concentration of the Eu 3+ dopant and the size of the phosphor particles.2-10 Upon increasing the Eu 3+ concentration between 1 and 15 Mol % a redshift of the E CT of about 6 nm has been observed, [2][3][4] whereas Kang et al. 5 did not observe a change of E CT in increasing the Eu 3+ dope from 2 to 10 Mol %. Some peculiar observations were reported on the effect of the particle size of Y 2 O 3 :Eu 3+ . Igarashi et al. 6 reported a blueshift of the E CT of 6 nm in reducing the particle size from 2.1 μm to 56 nm; Fu et al.7 measured a blueshift of 5 nm in reducing the particle size from 2.1 μm down to 10 nm. The opposite trend was found by others. Jia et al.8 measured a redshift of the E CT of 6 nm upon particle size reduction from 2-3 μm to 7 nm. Shang et al. 9 and Zhang et al. 10 reported large red shifts, 11 nm and 7 nm, in reducing the size of Y 2 O 3 :Eu 3+ nanoparticles from 40 nm to 9 nm and from 40 nm to 5 nm respectively. Semiconductor particles are expected to show a blueshift of their absorption peaks in reducing the particle size from 15 to 5 nm because of quantum confinement.11 The observed opposite trend indicates that quantum confinement cannot explain the reported ...
“…Several oxide host materials are available for the preparation of rare earth doped luminescent materials, but the Y 2 O 3 is chosen due to their high optical band gap, low phonon frequency and ionic radii comparable with most of the rare earths. Several studies have been reported on synthesis and optical characterisation of nanocrystalline Eu 3+ doped phosphors [7,8]. But, the upconversion (UC) emission with NIR excitation in singly Eu 3+ doped materials is not possible.…”
IntroductionThe rare earths (RE) doped luminescent materials have been the subject of significant interest in recent years due to their potential applications in different fields [1][2][3][4]. In these materials, mainly the rare earth elements are responsible for the generation of radiation of light of different color by changing the dopants, which are useful for various applications [5,6]. Several oxide host materials are available for the preparation of rare earth doped luminescent materials, but the Y 2 O 3 is chosen due to their high optical band gap, low phonon frequency and ionic radii comparable with most of the rare earths. Several studies have been reported on synthesis and optical characterisation of nanocrystalline Eu 3+ doped phosphors [7,8]. But, the upconversion (UC) emission with NIR excitation in singly Eu 3+ doped materials is not possible. So, in order to get visible UC emission from Eu 3+ ion, another rare earth ion can be used as sensitizer to excite Eu 3+ ions. In our previous study, we have excited Eu 3+ ion by a 980 nm laser using Er 3+ as sensitizer and studied its UC behavior [9]. In most of the cases, Yb 3+ ion is taken as the sensitizer because of its higher absorption crosssection corresponding to 980 nm excitation.In the present work, we have synthesized Y 2 O 3 : Eu 3+ -Yb 3+ phosphors through solution combustion synthesis process. The XRD analysis and upconversion emission studies of the synthesized material have been performed, and the process responsible for the UC emissions is discussed in detail.
Experimental ProcedureThe Eu
Results and Discussion
X-ray diffraction analysisThe X-ray diffraction pattern of heat treated Eu
AbstractFor structural information, the X-ray diffraction analysis of Y 2 O 3 :Eu 3+ phosphors codoped with Yb 3+ synthesized by combustion synthesis process has been performed. The upconversion emission study of the Y 2 O 3 :Eu 3+ phosphor codoped with Yb 3+ ions on excitation with 980 nm diode laser in the visible region has been done. The upconversion emissions corresponding to the Eu 3+ ions is due to sensitization from Yb 3+ ions in developed phosphor, and has been explained on the basis of cooperative energy transfer process. The orange colour emitted from the codoped samples is visualized by CIE diagram. The results show the applicability of the present phosphor as suitable NIR (near infrared) to visible upconverter, and in other photonic devices.
Journal of Physical Chemistry & Biophysics
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