Thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 were investigated by combined first-principles calculations and experimental evaluation. Theoretical calculation was used to predict the elastic properties, anisotropic minimum thermal conductivities, and temperature dependent lattice thermal conductivities. Experimentally, thermal conductivities of these disilicates were measured from room temperature to 1273 K. In addition, their experimental intrinsic lattice thermal conductivities were determined from the corrected thermal diffusivity data after removing the extrinsic contributions from phonon scattering by defects and thermal radiation. The experimental lattice thermal conductivities match well with the theoretical predictions. Furthermore, Raman spectra of the disilicates was measured and used to estimate the optical phonon relaxation time. The present results clearly disclose the specific material parameters that determine the low thermal conductivity of RE2Si2O7 and may provide guidelines for the optimal thermal conductivity of rare earth disilicates.

Exploration of the low thermal conductivities of γ-Y2Si2O7, β-Y2Si2O7, β-Yb2Si2O7, and β-Lu2Si2O7 as novel environmental barrier coating candidates

The structure of dilutetium silicon pentaoxide, Lu2SiO5, has isolated ionic SiO4 tetrahedral units and non-Si-bonded O atoms in distorted OLu4 tetrahedra. The OLu4 tetrahedra form edge-sharing infinite chains and double O2Lu6 tetrahedra along the c axis. The edge-sharing chains are connected to the O2Lu6 double tetrahedra by isolated SiO4 units. The structure has been determined by neutron diffraction.

Lu2SiO5 by single-crystal X-ray and neutron diffraction.

The structural and the optical properties of terbium-doped yttrium oxyorthosilicate phosphor particles were analyzed. The samples were prepared through an aqueous sol–gel route and investigated in ...

Optical and Structural Characterization of Terbium-Doped Y2SiO5 Phosphor Particles

Investigations of the luminescent properties of Pr-, Eu-, Tb- and Tm-implanted AlN thin films at temperature in the range 9 – 830 K are reported. The temperature studies of photoluminescence and cathodoluminescence spectra revealed unexpectedly weak thermal quenching for all investigated rare earth (RE) ions. The maximum CL emission is observed from Eu (red) at 485 K, Tb (green) at 590 K and Tm (blue) at 530 K, respectively. For Tb- and Tm-doped AlN samples, temperature-dependent crossrelaxation processes were observed. Photoluminescence excitation spectra, obtained under UV excitation in the spectral range 200 – 400 nm, exhibit several bands. It is proposed that the RE ions exist in semiconductors as isolated ions (singlet), nearest-neighbor (nn) ion pairs (dimer), and three ions (trimer). The Koster – Slater and simple spherical potential-well models for RE-structured isovalent (RESI) hole trap are proposed. The exciton binding energies of RESI traps are calculated and compared with experimental thermal-quenching energies. The energy-transfer processes between the AlN host and the 4f-shell systems are emphasized as the main mechanisms for thermal-quenching processes rather than nonradiative decay of 4f transitions.

Thermal quenching of luminescence and isovalent trap model for rare‐earth‐ion‐doped AlN

A bulk crystal of Yb:Sc2SiO5 (Yb:SSO) with favorable thermal properties was successfully obtained by the Czochralski method. The energy level diagrams for Yb:SSO crystal were determined by optical spectroscopic analysis and semi-empirical crystal-field calculations using the simple overlap model. The full width at half maximum of the absorption band centering at 976 nm was calculated to be 24 nm with a peak absorption cross-section of 9.2×10-21 cm2. The largest ground-state splitting of Yb3+ ions is up to 1027 cm-1 in a SSO crystal host. Efficient diode-pumped laser performance of Yb:SSO was primarily demonstrated with a slope efficiency of 45% and output power of 3.55 W.

Bulk crystal growth and efficient diode-pumped laser performance of Yb3+:Sc2SiO5

Infrared transmission and Raman scattering have been used to study Raman active phonons and crystal-field excitations in Yb3+-doped yttrium, lutetium and scandium orthosilicate crystals (Y2SiO5 (YSO), Lu2SiO5 (LSO) and Sc2SiO5 (SSO)), which belong to the same C2h6 crystallographic space group. Energy levels of the Yb3+ ion 2F5/2 manifold are presented. In the three hosts, Yb3+ ions experience high crystal field strength, particularly in Yb:SSO. Satellites in the infrared transmission spectra have been detected for the first time in the Yb3+-doped rare earth orthosilicates. They could be attributed to perturbed Yb3+ sites of the lattices or to magnetically coupled Yb3+ pairs.

https://iopscience.iop.org/article/10.1088/0953-8984/16/25/015/pdf

Spectroscopic studies of Yb3+-doped rare earth orthosilicate crystals

In this paper we investigate the optical effects of annealing under an oxygen atmosphere of Yb-doped Y2SiO5 thin films grown by liquid phase epitaxy. Infrared transmission, particularly adapted to thin film characterizations by means of Yb3+ crystal field excitations, is used to single out the effects of annealing. For instance, absorption intensities increase by ~10% and disorder in Yb3+ substitution is reduced. Micro-Raman backscattering measurements detect no particular defects in as-grown and annealed thin films.

Optical effects of annealing on Yb-doped Y2SiO5 thin films

Optical properties of Yb-doped Y2SiO5 thin films

Yb3+ crystal field excitations in ytterbium doped Y2SiO5 and Lu2SiO5 single crystals and thin films are studied under an applied magnetic field. The ground and excited state g-factors that are needed for the calculation of reliable crystal field Hamiltonian parameters are determined. Some of the Yb3+ ions that substitute for the Y3+ or Lu3+ ions give rise to Yb3+–Yb3+ magnetically interacting pairs as confirmed by their crystal field absorption bands under a magnetic field. The overall crystal field excitation characteristics confirm the strong similarities between the single crystals studied and thin films.

http://iopscience.iop.org/article/10.1088/0953-8984/20/12/125227/pdf

A Denoyer

Papers

Spectroscopic studies of Yb3+-doped rare earth orthosilicate crystals

Optical effects of annealing on Yb-doped Y2SiO5 thin films

Optical properties of Yb-doped Y2SiO5 thin films

Crystal field study of ytterbium doped Lu2SiO5 and Y2SiO5 under a magnetic field