Structural and Optical Properties of NdAlO₃ Nanocrystals Embedded in an Al₂O₃ Matrix

Abstract

Fabrication of an oxide−oxide nanocomposite, containing a homogeneous dispersion of NdAlO3 nanocrystals in an Al2O3 matrix, is achieved by employing a single molecular compound, [NdAl3(OPri)12(PriOH)], in the sol−gel process. X-ray diffraction patterns of the composite material show NdAlO3 to be the only crystalline phase, up to 1200 °C, with an equimolar part of amorphous Al2O3. The crystallization of alumina (δ-, γ- and κ-phases) occurs at higher temperatures (>1300 °C). TEM investigations reveal a bimodal distribution of particles where NdAlO3 crystallites are uniformly dispersed in an amorphous Al2O3 matrix. HR-TEM analysis shows a composite structure formed by NdAlO3 nanocrystals (50−60 nm) homogeneously incorporated in a matrix of smaller alumina particles (10−12 nm). The existence of two chemically different Al(III) species (Al2O3 and NdAlO3), in the composite, is proven by 27Al solid-state NMR and XPS studies. The line deconvolution of the Al 2p XPS spectrum reveals two components in a 1:2 ratio with binding energies corresponding to pure NdAlO3 and Al2O3. The diphasic nature of the oxide composite is also established by oxygen content analysis. The influence of the alumina matrix on the structural and optical properties of NdAlO3 dispersoids was evaluated by comparing the results of grain growth and photoluminescence of the NdAlO3/Al2O3 nanocomposite (NA3) with those for a nanocrystalline sample of monophasic neodymium aluminate (NA), obtained by the hydrolytic decomposition of the molecular precursor [NdAl(OPri)6(PriOH)]2. The absorption and photoluminescence (PL) spectra of NA and NA3 systems exhibit an enhanced performance in the composite material due to the effect of the NdAlO3−Al2O3 interface and the fact that the Al2O3 matrix functions as a spacer among the NdAlO3 nanocrystals. The PL efficiency was nearly 35 times higher in NA3 than in NA, which is attributed to the control of the minimum Nd−Nd separation within and on the surface of NdAlO3 nanocrystals coupled with the cooperative energy transfer of the absorbed pumping energy from Al3+ to Nd3+ ions via the F + centers present in the alumina matrix. The results illustrate that the use of single-source precursors can impose a strict stoichiometry control at the nanometer scale in monophasic ceramics and a homogeneous dispersion of one phase into another in nanocomposites.

Nanowatt threshold, alumina sensitized neodymium laser integrated on silicon

“…First, as observed in the previous section, the refractive index increases with increasing alumina concentration causing the quality factor to also increase. Second, when alumina is added to Nd 3+ -doped silica, the optical absorption coefficient has been observed to decrease due to more favorable coordination of Nd 3+ with alumina in the silica [18,24]. Therefore, high quality factors of over 1 million can be achieved in the alumina-containing devices.…”

“…At greater alumina concentrations, more neodymium ions are coordinated with Al-O bonds instead of Si-O bonds. When coordinated with alumina, the Nd 3+ ions have reduced clustering, quenching and nonradiative decay compared to plain silica [18,21,24]. In addition, the alumina has a lower phonon energy than the sol gel silica, causing the Nd 3+ emission to blue shift slightly [18,21,24].…”

Magnetic susceptibility and surface properties of EuAlO3 nanocrystals

“…The gel was transferred in a Pt crucible and oven-dried (383 K) for 2 h. The gel powder was ground in an agate mortar and preheated for 3 h at 1073 K in air. The gel is very combustible, especially between 373 K and 673 K. mediate grinding, the yellow powder was additionally sintered in air for 8 h at 1223 K. The precursor gel yields perovskite aluminates as end products [9,10]. The temperature of final annealing was chosen to be below the reported orthorhombic to rhombohedral phase-transition temperature.…”

Influence of Metal Fragment Mobility and Solution Dynamics on Cationic Rearrangements in Multimetallic Alkoxide Frameworks

“…[1][2][3][4][5][6][7][8][9] The preorganized metal À oxygen (alkoxy) bonds and the intrinsic reactivity against nucleophilic attack as well as the thermally labile nature of the organic periphery makes metal alkoxides ([M(OR) x ], [MM'(OR) x + y ]) as preferred starting materials for sol À gel and chemical vapor deposition processes. [2,[10][11][12][13][14][15][16] Metal-organic compounds in general enable low temperature processing of nanostructured oxides and their solid-solutions or composites that are challenging to obtain by traditional solid-state reactions. [10-13,17À21] Among functional metal oxides, cerium oxides are of potential importance both as monophasic material and particularly in conjunction with other metal oxides due to their reducible nature and oxygen capturing properties shown in solid-oxide fuel cells and high temperature sensor applications.…”