Thermal effects on cathodoluminescence in forsterite

Cathodoluminescence (CL) spectral analysis has been conducted for luminescent forsterite (olivine) of terrestrial and meteoritic origins. Two emission bands at 3.15 and 2.99 eV in blue region can be assigned to structural defect centres and two emission bands at 1.91 and 1.74 eV in red region to impurity centres of Mn²⁺ and Cr³⁺, respectively. These emissions reduce their intensities at higher temperature, suggesting a temperature quenching phenomenon. The activation energy in the quenching process was estimated by a least-square fitting of the Arrhenius plots using integrated intensity of each component as follows; blue emissions at 3.15 eV: 0.08–0.10 eV and at 2.99 eV: 0.09–0.11 eV, red emissions at 1.91 eV: ～0.01 eV and at 1.74 eV: ～0.02 eV. The quenching process can be construed by the non-radiative transition by assuming the Mott-Seitz model. The values of activation energies for blue emissions caused by structural defects correspond to the vibration energy of Si-O stretching mode in the lattice, and the values for red emissions caused by Mn and Cr impurity centres to Mg-O vibration energy. It implies that the temperature quenching energy might be transferred as a phonon to the specific lattice vibration.     

Development and Performance Evaluation of Disk-Type Piezoelectric Transducer for Measurement of Shear and Compression Wave Velocities in Soil

A piezoelectric transducer capable of measuring both shear and compression wave velocities in soil simultaneously in triaxial testing conditions is presented. Performance evaluation of disk transducer system showed that the use of low-noise coaxial cables, proper grounding, and high resolution wave recorder can significantly enhance signal quality and eliminates crosstalk deterioration. Distortions due to near-field effects were found to diminish by increasing input frequency and by using sinusoidal input waveform, compared to square input. Disk-type piezoelectric transducers show significant future potential for laboratory determination of shear, and compression modulus of soil because of their robustness and noninvasive nature.