Low-temperature phase equilibria ranging from 1000" to 1200°C in the Zr0,-CeO, system were investigated by annealing compositionally homogeneous Zr0,-CeO, solid solutions in a Na,B,O,.NaF flux. The 5 mol% CeO, samples decomposed into monoclinic ( m ) and tetragonal ( t ) phases during annealing at 1100" and 1120"C, and the t-phase transformed diffusionlessly into monoclinic (m') symmetry during quenching. A eutectoid reaction, t +-( m + c), was confirmed to occur at 1055" +. 1O"C, where the equilibrium compositions of the t-, m-, and c-phases were 11.2 +: 2.8, 0.9 f 0.9, and 84 ? 1 mol% CeO,, respectively. The equilibrium phase boundaries were almost independent of the annealing time and/or the flux:sample ratio, which indicates that the flux accelerates the reaction rate without affecting the equilibration. The previous data are discussed using metastable-stable phase diagrams. The discrepancies of the low-temperature phase diagram in the literature are attributable to either regarding the metastable phase boundaries as stable ones or ignoring the sluggish kinetics.

DSC (differential scanning calorimeter) measurements were performed to investigate the tetragonal‐monoclinic (t‐m) transition enthalpy of the compositionally homogeneous ZrO2‐X mol% CeO2 solid solution of X= 0, 4, 8, and 12. The transition enthalpy decreases linearly with an increase of CeO2 content. The m → t transition enthalpy on heating agreed well with the inverse t → m one obtained during cooling. With increasing X, the DSC peak broadens and the transition temperature distribution of each sample increases, while the thermal hysteresis is almost independent of X.

A monolayer of silicon quantum dots (Si-QDs) 2.8 and 3.9 nm in diameter is placed in a gap between a gold (Au) thin film and a Au nanoparticle, and the photoluminescence (PL) properties are studied. By the metal nanoparticle over mirror (MNPoM) structure, the PL spectra of Si-QDs are strongly modified; the full width at half-maximum is reduced to ∼170 meV, which is less than half of that of Si-QDs on a silica substrate. The spectral shape coincides almost perfectly with that of the scattering spectrum of the MNPoM structure, indicating efficient coupling of the luminescence of Si-QDs with the gap surface plasmon modes. The luminescence intensity of Si-QDs in the gap is estimated to be enhanced about 700-fold compared to those on a Au film.

An upconversion composite nanoparticle (NP) composed of an Er and Yb doped Y2O3 (Y2O3:Yb,Er) NP and a Au nanocap was developed, and the effect of the coverage on the optical responses was studied by numerical simulations and optical measurements of single composite NPs. The formation of a composite NP and the control of the coverage were confirmed by transmission electron microscope observations. By controlling the coverage, the scattering peak due to the magnetic dipole surface plasmon resonance shifted from around 700 nm to over 900 nm. The upconversion intensity was also strongly modified by the coverage. Clear correlation was observed between the surface plasmon resonance wavelength and the upconversion intensity; the intensity increased as the resonance wavelength approached the excitation wavelength (975 nm). The largest enhancement factors of the upconversion with respect to that of a Y2O3:Yb,Er NP without a Au nanocap were 64 and 101-fold for the green (∼560 nm) and red (∼660 nm) emissions, respectively.