Confinement effects in sesquioxydes (original) (raw)
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Effect of the quantum confinement on the luminescent properties of sesquioxydes
Journal of Luminescence, 2007
Spectroscopic behaviour of Y 2 O 3 :Ce 3+ nanocrystals are presented. A new fluorescence peaking around 430nm appears in small particles. This emission is interpreted as the 5d-4f radiative recombination of Ce 3+ which does not occur in bulk materials due to autoionisation processes. This change in behavior could be due to both quantum confinement inside the nanoparticles and changes in the crystal field for small sizes corresponding author:Christophe Dujardin, LPCML, 10 rue Ampère 69622 Villeurbannes Cedex. Tel (33) 4 72 43 12 08, Fax (33) 4 72 43 11 30,
Luminescence Concentration Quenching Mechanism in Gd 2 O 3 :Eu 3+
The Journal of Physical Chemistry A, 2014
Luminescence concentration quenching in Gd 2 O 3 :Eu 3+ nanocrystals results from strong interactions among O 2− ions and Eu 3+ ions. Because all synthesized Gd 2 O 3 :Eu 3+ nanocrystals present the same cubic crystalline phase regardless of Eu 3+ concentration, it is possible to study the optical properties as a function of the dopant concentration. The emission intensities and lifetime curves for Gd 2 O 3 :Eu 3+ were analyzed by a simple rate equation model to study the interaction between the O 2− ions and Eu 3+ ions. The rate equation model considers that such interaction is driven by the following energy transfer processes: the direct energy transfer (O 2− → Eu 3+ ), back-transfer (Eu 3+ → O 2− ), and direct energy migration (Eu 3+ → Eu 3+ ). The exact solution of this model agrees with the experimental results, luminescence concentration quenching is reproduced and the corresponding energy transfer rates are reported. Quantitative results suggest that the direct energy transfer and direct energy migration processes are the main responsible for the luminescence concentration quenching, whereas the back-transfer process promotes the Eu 3+ emission.
Radiation Measurements, 2004
This paper reports on the synthesis and characterization of Gd2O3:Eu 3+ nanocrystals of di erent sizes. The particles have been synthesized by a sol-lyophilization process. This methods allows the synthesis of 7-100 nm diameter cubic-phase particles. The photoluminescence properties have been studied with di erent excitation from X-ray to VUV and visible wavelengths. Compared to the properties of the bulk materials, some important changes on the luminescence are observed. In particular some bands are strengthened when the size of the particles is diminished. We could therefore ascribe this bands to doping ions on a site close to the surface. Also a very low e ciency of excitation for small particles is observed when exciting with X-ray or high-energy VUV photons (i.e. when exciting the host matrix) compared to the e ciency obtained when exciting in the charge transfer band or in the doping ions related states.
Morphology- and size-dependent spectroscopic properties of Eu3+-doped Gd2O3 colloidal nanocrystals
Journal of Nanoparticle Research, 2014
The synthesis, morphological characterization, and optical properties of colloidal, Eu(III) doped Gd 2 O 3 nanoparticles with different sizes and shapes are presented. Utilizing wet chemical techniques and various synthesis routes, we were able to obtain spherical, nanodisk, nanotripod, and nanotriangle-like morphology of Gd 2 O 3 :Eu 3? nanoparticles. Various concentrations of Eu 3? ions in the crystal matrix of the nanoparticles were tested in order to establish the levels at which the concentration quenching effect is negligible. Based on the luminescence spectra, luminescence lifetimes and optical parameters, which were calculated using the simplified Judd-Ofelt theory, correlations between the Gd 2 O 3 nanoparticles morphology and Eu 3? ions luminescence were established, and allowed to predict the theoretical maximum quantum efficiency to reach from 61 to 98 %. We have also discussed the impact of the crystal structure of Gd 2 O 3 nanoparticles, as well as coordinating environment of luminescent ions located at the surface, on the emission spectra. With the use of a tunable femtosecond laser system and the Z-scan measurement technique, the values of the effective two-photon absorption cross-section in the wavelength range from 550 to 1,200 nm were also calculated. The nonlinear optical measurements revealed maximum multi-photon absorption in the wavelength range from 600 to 750 nm.
Optical studies of sub-3nm Eu2O3 and Gd2O3:Eu3+ nanocrystals
Journal of Alloys and Compounds, 2009
Colloidally stable sub-3 nm Eu 2 O 3 and Gd 2 O 3 :Eu 3+ nanocrystals have been synthesized via a hot solution phase technique. Optical properties of the nanocrystals are studied as a function of size. Both nanocrystal compositions exhibit a new optical signature, an emission peak at 620 nm. Intensity modulation of this peak has been observed for all nanocrystal sizes, suggesting surface-dependent or crystal-field dependent effect. Photoluminescence intensity of smaller Eu 2 O 3 nanocrystals was comparable to that of the Gd 2 O 3 :Eu 3+ nanocrystals.
uminescence Concentration Quenching Mechanism in Gd2O3:Eu3+.
Luminescence concentration quenching in Gd2O3:Eu3+ nanocrystals results from strong interactions among O2− ions and Eu3+ ions. Because all synthesized Gd2O3:Eu3+ nanocrystals present the same cubic crystalline phase regardless of Eu3+ concentration, it is possible to study the optical properties as a function of the dopant concentration. The emission intensities and lifetime curves for Gd2O3:Eu3+ were analyzed by a simple rate equation model to study the interaction between the O2− ions and Eu3+ ions. The rate equation model considers that such interaction is driven by the following energy transfer processes: the direct energy transfer (O2− → Eu3+), back-transfer (Eu3+ → O2−), and direct energy migration (Eu3+ → Eu3+). The exact solution of this model agrees with the experimental results, luminescence concentration quenching is reproduced and the corresponding energy transfer rates are reported. Quantitative results suggest that the direct energy transfer and direct energy migration processes are the main responsible for the luminescence concentration quenching, whereas the back-transfer process promotes the Eu3+ emission.
Judd−Ofelt Intensity Parameters and Spectral Properties of Gd2O3:Eu3+ Nanocrystals
The Journal of Physical Chemistry B, 2006
Three nonequivalent centers of C s (A, B, and C) in monoclinic phase and C 2 and S 6 centers in cubic phase were identified in the Gd 2 O 3 :Eu 3+ nanocrystals with spectral techniques. Size dependence in the spectra indicated that the excitations from both host and charge-transfer band (CTB) for the 5 D 0 f 7 F 2 transition of Eu 3+ ions were nearly equal for a larger size of 135 nm of the cubic phase; however, with decreasing the size to or less than 23 nm, the excitations by the CTB dominated. The variation of excitation leading to the symmetry and energy change in the C 2 and S 6 sites was also observed for larger particle sizes. The Judd-Ofelt intensity parameters Ω λ (λ) 2, 4) for Gd 2 O 3 :Eu 3+ nanoparticles were experimentally determined. The parameters Ω λ were found to significantly change with the sizes of Gd 2 O 3 :Eu 3+ from nanoparticles to bulk material. With decreasing the size from 135 to 15 nm, the quantum efficiencies for 5 D 0 reduced from 23.6% to 4.6% due to the increasing ratio of surface to volume.
Diffusion and Defect Data Pt.B: Solid State Phenomena, 2007
Rare earth doped materials have many familiar applications (TV screens, solid lasers, scintillators…) thanks to their efficient and robust luminescence properties. In recent years, growing interest has been focused on the changes in their optical properties with the size of the host particles. In this work, nanomaterials were produced for the first time by using laser pyrolysis. Y, Gd, and Eu nitrates were dissolved in water and used as precursors. Cubic phases of Y 2 O 3 :Eu 3+ and Gd 2 O 3 :Eu 3+ were obtained with sizes ranging from 3 to 40 nm. The spectroscopic properties revealed a new and nanostructure-specific broad band in the excitation spectrum. The emission spectrum was found to be characteristic of nanostructured sesquioxides only when excited in this new band, which was finally assumed to be a new charge transfer band for the smallest nanoparticles in the sample.
Spherical and rod-like Gd 2 O 3 :Eu 3 + nanophosphors—Structural and luminescent properties
Bulletin of Materials Science, 2012
A comparative study of spherical and rod-like nanocrystalline Gd 2 O 3 :Eu 3+ (Gd 1•92 Eu 0•08 O 3) red phosphors prepared by solution combustion and hydrothermal methods have been reported. Powder X-ray diffraction (PXRD) results confirm the as-formed product in combustion method showing mixed phase of monoclinic and cubic of Gd 2 O 3 :Eu 3+. Upon calcinations at 800 • C for 3 h, dominant cubic phase was achieved. The as-formed precursor hydrothermal product shows hexagonal Gd(OH) 3 :Eu 3+ phase and it converts to pure cubic phase of Gd 2 O 3 :Eu 3+ on calcination at 600 • C for 3 h. TEM micrographs of hydrothermally prepared cubic Gd 2 O 3 :Eu 3+ phase shows nanorods with a diameter of 15 nm and length varying from 50 to 150 nm, whereas combustion product shows the particles to be of irregular shape, with different sizes in the range 50-250 nm. Dominant red emission (612 nm) was observed in cubic Gd 2 O 3 :Eu 3+ which has been assigned to 5 D 0 → 7 F 2 transition. However, in hexagonal Gd(OH) 3 :Eu 3+ , emission peaks at 614 and 621 nm were observed. The strong red emission of cubic Gd 2 O 3 :Eu 3+ nanophosphors by hydrothermal method are promising for high performance display materials. The variation in optical energy bandgap (E g) was noticed in as-formed and heat treated systems in both the techniques. This is due to more ordered structure in heat treated samples and reduction in structural defects.
Journal of Applied Physics, 2008
Nanoparticles of GdVO 4 doped with Eu 3+ and core/shell of GdVO 4 :Eu 3+ / GdVO 4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130°C. Unit cell volume increases when GdVO 4 is doped with Eu 3+ indicating the substitution of Gd 3+ lattice sites by Eu 3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu 3+. Optimum luminescence intensity is found to be in 5-10 at. % Eu 3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu 3+ surroundings by bonding to GdVO 4 shell. The lifetime for 5 D 0 level increases with annealing and core/shell formation.