Optical absorption and emission properties of Gd in silica host

We present a study of the optical properties of Gd-doped sol-gel silica glasses densified at different temperatures (from 450 up to 1050 °C) by means of optical absorption (OA) and radio luminescence (RL). The effect of a post-densification rapid thermal treatment (RTT) at approximately 1800 °C is also considered. Room temperature OA and RL measurements have revealed a slight low-energy shift of Gd³⁺ absorption/emission lines by densification temperature increasing accompanied by a parallel increase of Gd³⁺ RL intensities, especially strong after RTT. These effects are interpreted on the basis of structural modifications of the silica matrix and of the removal of non-radiative channels competing with Gd³⁺ emission. Moreover, RL spectra of fully densified samples display high-energy shoulders on the ⁶P_7/2-⁸S Gd³⁺ emission possibly related to crystal field splitting of the ⁶P_7/2 state. This interpretation is supported by the temperature dependence of RL spectra, investigated in the 10-320 K temperature interval: an increase of the intensity of high-energy components vs. temperature has been observed, which can be interpreted as due to thermally assisted excitation of electrons belonging to the lower ⁶P_7/2 state to higher crystal field states and their subsequent radiative recombination.     

Channel waveguides in Ca4GdO(BO3)3 fabricated by He+ implantation for blue-light generation

Blue light at 405 nm is generated by frequency doubling of a Ti:sapphire tunable laser in He(+)-implanted channel waveguides in gadolinium calcium oxoborate crystal. A conversion efficiency of approximately 2% W(-1) cm(-2) is achieved between TM00 fundamental and TE01 harmonic modes.     

On the temperature dependence of the g shift in Nd3+:YES

A temperature-dependent contribution to the g factor of Nd³⁺:YES has been observed. A semi-empirical theory of the phenomena is presented in which the matrix elements of the dynamic crystal field potential are evaluated starting from spin-lattice relaxation rates. The evaluated contribution is in good agreement with the observed g shift.     

Substituent effect on the 1H NMR Spectra of trans aryl methyl oxiranes and arylpropenes

The ¹H NMR spectra of 1-aryl-2-methyl oxiranes substituted in the phenyl ring and of the corresponding vinyl derivatives have been analysed. The substituent effect on oxiran protons seems mostly polar in character, as shown by correlations with substituent constants, solvent effects and the fact that perturbation decreases with increasing distance from the substituent. The comparison with the corresponding vinyl derivatives, in which conjugation effects are present, confirms this point. The results also seem to exclude the possibility of substituents causing significant changes on the preferred conformation of the phenyl ring. Ring current contributions on oxirane protons, evaluated by SCF procedure, show that their change with substituents is very small and does not represent a significant part of the change of proton chemical shift with substituents.     

New laser lines from optically pumped CH3OH: measurements and assignments

New CW FIR laser lines from optically pumped CH₃OH are reported. Experimental values for wavelength, polarization and pump offsets are given. Lines assignments are proposed. New experimental results and possible assignments are also given for previously reported lines.     

Assignment of Fir Laser Lines of Fully Deuterated Dichloromethane

We have recently reported 16 new far-infrared laser emissions of CD₂Cl₂. While the overwhelming majority of the previously known FIR laser emissions of this molecule were polarized parallel to the polarization of the pump CO₂ line, 13 of our 16 new lines are polarized perpendicularly to the exciting CO₂ radiation. In principle, the presence of perpendicular/parallel emission pairs is extremely important for the assignment of laser transitions. In the present work we discuss the possible assignments of 16 far-infrared (FIR) laser emission pairs of CD₂Cl₂.     

Performance of W-InSb Metal-Semiconductor Point-Contact Diodes as Detectors and Mixers in the Near Infrared

Metal-Insulator-Metal (MIM) and Schottky-barrier diodes have been used extensively in the past years as harmonic generators and mixers for frequency measurements in the spectral range from the far-infrared to the visible. MIM diodes present a very low fabrication cost and are easy to handle, while Schottky diodes are mechanically more stable and long-lived. In the present work we discuss the performance of a metal-semiconductor point-contact diode for the radiation around 1 m. This device, which may be viewed as a hybrid between a MIM and a Schottky diode, combines the simplicity and easiness of fabrication of the MIM diode with the stability and the long contact life typical of the Schottky diode. It proved to be very efficient even for visible light.