We report on structural, magnetic, optical, and dielectric properties of rare earth (Er and Yb)-doped ZnO nanoparticles with Na-co-doping for charge compensation by sol-gel process. The effect of doping concentration on the structural and dielectric properties of ZnO has been studied under magnetic field and UV excitation. The magnetodielectric and photodielectric effects at room temperature of doped ZnO are discussed in the light of magnetic and optical properties of Er3+ and Yb3+ ions.

We report on photo-induced magnetic effect and infrared (IR) spectroscopic behavior of colossal magnetorestive manganite La0.7Sr0.3MnO3 (LSMO) with rare earth co-doping (Er3+ and Yb3) at room temperature. X-ray diffraction shows that a structural phase transformation from rhombohedral to hexagonal with increasing Er and Yb concentrations. Photo-induced magnetoresistance showed that Er3+ and Yb+3 ions have significant influence on the magnetic and electrical ordering of LSMO under the influence of UV light. The optical excitation also shows an enhancement in the magnetotransport properties of LSMO.

Standard molar heat capacity, $C_{{\rm{p,m}}}^{\rm{o}}\left( T \right)$, of YbRhO3(s) was determined using a heat flux type differential scanning calorimeter from 126 to 846 K. The heat capacities in the temperature range 307 ≤ T (K) ≤ 846 were fitted into a polynomial expression and can be represented by $C_{{\rm{p,m}}}^{\rm{o}}$ (YbRhO3, s, T) [J/(K mol)] = 106.82 + 8.57 × 10−3T (K) − 9.48 × 105/T2(K). The standard molar heat capacity of YbRhO3(s), $C_{{\rm{p,m}}}^{\rm{o}}$, at 298.15 K is 98.7 J/(K mol). The standard molar Gibbs energy of formation of YbRhO3(s) was also determined using calcia stabilized zirconia as an oxide electrolyte and air as the reference electrode by the solid state electrochemical technique. The cell can be represented by (−)Pt–Rh/{Yb2O3(s) + YbRhO3(s) + Rh(s)}//CSZ//O2(p(O2) = 21.21 kPa)/Pt–Rh(+). The electromotive force was measured in the temperature range from 889 to 1110 K. The standard Gibbs energy of formation of YbRhO3(s) from elements in their standard state can be represented by ΔfGo{YbRhO3(s)}/kJ/mol(±1.62) = −1110.9 + 0.287 T (K). The heat capacity of YbRhO3(s) was used along with the data obtained from the electrochemical cell to evaluate all thermodynamic functions of YbRhO3(s).

Spectroscopic imaging and statistical analysis of NIR-to-visible upconversion luminescence (UCL) from β-NaYF4:Yb3+:Er3+ upconverting nanoparticles (UCNPs) supported on a series of random Ag nanowire aggregates reveals a density dependent UCL enhancement. Statistical analysis of the spectrally resolved upconversion images shows a non-linear dependence of upconversion luminescence enhancement with Ag nanowire surface coverage. A maximum average enhancement of 5.8× was observed for 58% surface coverage. Based on the empirically determined trend with density, it is estimated that up to 20× upconversion luminescence enhancement can be achieved at 100% surface coverage, even at high excitation intensity. This projection is commensurate with the 20× enhancement ratio observed for select locations within the imaged micro-ensemble. Time-resolved emission of the UC luminescence from UCNPs on the Ag nanowire aggregates confirms the surface plasmon effects on the UCNPs kinetics. Such Ag nanowire aggregates show potential as a scalable and relatively simple metal-enhanced upconversion substrate.

Tb and Yb co-doped oxyfluoride glasses were fabricated in a lithium-lanthanum-aluminosilicate matrix by a melt-quench technique. Glass-ceramics were obtained by appropriate heat treatment of the as-prepared glasses. Visible to near-infrared down-conversion quantum cutting was studied for samples with different thermal annealing temperatures and time. Laser light at 488 nm was used to excite Tb3+ ions while Yb3+ ions were excited by energy transfer from the excited Tb3+ ions. Near-infrared emission at 940 – 1020 nm was observed. It has been found that the emission at 940 – 1020 nm increased significantly from the glass-ceramic compared to that of the as-prepared glass. This result suggests that the energy-transfer efficiency increases in glass-ceramics compared to that in glass. A significant portion of rare-earth ions may be incorporated inside LaF3 nanoparticles (NPs) in the glass-ceramic. Because the Yb3+ emission at 940 – 1020 nm is matched well with the band gap of crystalline Si, the quantum cutting effect may have its potential application in silicon-based solar cells.

Near-infrared quantum cutting involving the conversion of one visible photon into two near-infrared photons was demonstrated in Ca0.99−xYbxWO4: Tb0.01 phosphors. From the analysis of the refinement of x-ray diffraction patterns, the suitable concentration range of Yb3+ in Ca0.99WO4: 0.01Tb3+ was determined to be 0–20%. By investigating their luminescent spectra and decay lifetimes, second-order downconversion from Tb3+ to Yb3+ were proved and the possible quantum cutting mechanism was proposed. Quantum efficiency related to Yb3+ concentration was calculated and the maximum efficiency was reached at 140.4%. Because the energy of Yb3 + 2F7/2 → 2F5/2 transition matches well with the band gap of the crystalline Si, the Ca0.99−xYbxWO4: Tb0.01 phosphors could be potentially applied in silicon-based solar cells.

ZrO2:Yb3+ nanocrystalline phosphors with high concentrations of ytterbium ions were prepared using the sol-gel method. X-ray diffraction, high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the nanocrystalline phosphors annealed at 1000°C. Unit-cell distortion and changes in the crystalline structure of the monoclinic zirconia to tetragonal zirconia, and subsequently cubic zirconia, were observed with increased Yb concentration. Yb ions were randomly distributed into the lattice of the crystalline structure. No segregation of Yb2O3 phase was observed. The substitution of Zr atoms by Yb atoms on different crystalline phases was confirmed by the experimental results and theoretical simulations of HRTEM and HAADF-STEM.

We clarify here certain aspects of the magnetic field (H) – temperature (T) phase diagram of YbMnO3, a hexagonal Rare-Earth manganite oxide in which two multiferroic ordered states – ferroelectricity and antiferromagnetism coexist at low temperature. Single crystals of YbMnO3 were carefully grown from a Floating Zone (FZ) at low speed, then oriented and studied at variable temperature and magnetic field. Magnetization and heat capacity measurement show features corresponding to the antiferromagnetic (AFM) ordering of Mn3+, and the rare earth Yb3+. We find that the ordering temperature of Mn3+ is independent of applied magnetic field up to 5T. However, contrary to previous reports in flux-grown crystals, we do not observe a complete suppression of Yb3+ order above 0.1T. Instead, we find that Yb3+ remains at least up to 1 T, suggesting a revision of our current understanding of the ordering mechanism of the Mn-Yb and Yb –Yb sub-lattices in this hexagonal structure.

Luminescence properties of Yb-doped Ca-α-SiAlON phosphors with composition of Ca1−xYbxSi12−(m+n)Alm+nOnN16−n were investigated by using cathodoluminescence (CL). The ratio of Yb to Ca was kept constant while the host lattice was changed by replacing m+n(Si–N) bonds with m(Al–N) and n(Al–O) bonds. The luminescence of these phosphors consists of three peaks in the ultraviolet (UV), green (VIS), and infrared (IR) regions, which are attributed to the emissions from secondary phases, Yb2+ and Yb3+, respectively. The UV emission depends on the Si/Al ratio: the UV peak is centered at 310 nm for the Si-rich mix and at 360 nm for the Al-rich mix. We have found that Yb exists in the divalent state in α-SiAlON and in the trivalent state in the secondary phases.