Nobuhiro Kodama

Optical and electron spin resonance spectroscopy of Ti3+ and Ti4+ in Al2O3

The absorption spectrum of Ti3+:Al2O3 crystals grown in a reducing atmosphere consists of the main blue‐green absorption band and a weak infrared band. This infrared absorption decreases in intensity on annealing the as‐grown samples in a reducing atmosphere. The analysis of electron spin resonance spectra of the as‐grown samples, in which the infrared absorption band is observed, indicates that the center associated with the band is a cluster involving Ti3+ and Ti4+ ions with a neighboring, charge compensating Al3+ vacancy. The coexistence of a Ti4+ ion and an Al3+ vacancy in the neighborhood of the Ti3+ ion weakens the crystal field at this ion more than a single Ti4+ ion, giving rise to a red shift of the Ti3+ absorption.

Inhomogeneous broadening of the luminescence in

Five absorption bands with peaks at , 246 nm, 284 nm, 296 nm, and 368 nm were observed at room temperature for Ce-doped (CYA) crystals grown in a reducing atmosphere. Excitation at wavelengths below of Ce:CYA crystals produces a broad luminescence band with a peak at . The excitation spectrum of the luminescence detected at a fixed wavelength of 485 nm is very similar to the absorption spectrum. The ultraviolet absorption and visible luminescence are due to the transitions of ions in CYA. The linear dependence of the luminescence peak energy on the excitation energy shows that the luminescence is inhomogeneously broadened by a random distribution of and ions in the disordered CYA lattice.

A study of substitutional disorder in : I. Fluorescence line narrowing

A high-resolution study of the optical properties of -doped is presented. Excitation into the usual broad absorption bands produces fluorescence from a very broad line with a peak at at 15 K. The line is observed at an energy higher at temperatures above 100 K or by using excitation spectroscopy. The large broadening of the excited state is attributed to substitutional disorder at the and sites on the basis of site selective excitation and fluorescence line narrowing measurements. Estimates of the distributions of octahedral and non-octahedral contributions to the crystal field are made and it is shown that the non-octahedral crystal field is dominant.

A new crystal growth method for in situ core doping

Abstract A new crystal growth method enabling the preparation of modulation-doped crystal rods has been proposed. Two crucibles combined with an outer and inner die were used for transport of separate doped melts to a single growth interface. Core doped Nd,Cr:LiNbO 3 crystals with a sharply separated central doped region were grown successfully. The growth conditions, the radial dopant distribution and the advantages of these types of crystals are discussed.

Room-temperature persistent spectral hole burning of Sm2+ in disordered fluorite-type single crystals α-MALnF6 (M=Ca, Sr; A=Na, K, Rb; Ln=Y, La)

Abstract Persistent spectral hole burning is observed in Sm 2+ doped disordered fluorite-type single crystals α-MALnF 6 ( M = Ca , Sr ; A = Na , K , Rb ; Ln = Y , La ) at room temperature. The holes are burned in the 7 F 0 → 5 D 0 lines of the Sm 2+ in the cation disordered fluorite-type crystals. The compositional dependences of the inhomogeneous line width and the hole width are also measured.

Passive Mode Locking of a Flashlamp-Pumped Ti:Sapphire Laser

Passive mode locking with a saturable absorber was observed in a flashlamp-pumped titanium-doped sapphire laser. The peak wavelength of the absorption spectrum of the saturable absorber (IR-125 dye) was almost the same as that of the gain spectrum of the titanium doped sapphire. The pulse durations of the mode-locked laser were about 100 ps.

A study of substitutional disorder in : II. Electron spin resonance and polarization of optical spectra

Electron spin-resonance (ESR) studies of in (CYA) reveal spectra consisting of fine-structure pairs of narrow symmetric lines and fairly broad asymmetric lines, corresponding to ions in sites with ordered and disordered configurations of the second-nearest-neighbour ions, respectively. The polarized intensities of the absorption band and the -line fluorescence, measured with the E-vector of the radiation parallel and perpendicular to the c-axis, are in the ratio . These polarization ratios suggest that the octahedra undergo an angular distortion such that the magnetic -axis of the spectrum is rotated away from the crystal c-axis. The microstructure of the surrounding is discussed in terms of the ESR and polarization results.

E/O Q-Switching of a Flashlamp-Pumped Ti:Sapphire Laser

E/O-Q-switching of a flashlamp pumped Ti:Sapphire laser was demonstrated. The laser was simulated by the simple rate-equations. Effective improvements for obtaining higher peak power were predicted by computer simulation. These improvements included increased input power, reduced optical loss, and optimized output coupler.

Luminescence of Tris(2,2'-bipyridine)ruthenium(II) Incorporated in Mica-Organic Polymer Intercalation Compounds

Abstract Luminescence of Ru (bpy)32+ incorporated in a swelling mica-poly(vinylpyrrolidone)(PVP) intercalation compound was investigated. In the sterically limited interlayer space of mica, Ru(bpy)32+ was forced to be surrounded by PVP in close contact, showing a novel controlled luminescent behavior.

EPR and optical spectroscopy of Cr3+ doped CaYAIO4

EPR and optical measurements have been carried out on Cr 3+ doped CaYAlO 4 at 1.6 K, 16 K and 300 K. Q-band measurements revealed a strong, asymmetric EPR line close to g≃2 for B//c, together with three weak fine-structure lines corresponding to tetragonal symmetry. The R 1 line of Cr 3+ has an inhomogeneous broadened linewidth of about 100 cm -1 at 16 K but a homogeneous width of less than 10 cm -1 , the measurement of which was monochromator slit width limited. The large inhomogeneous broadening of the optical and EPR spectra are attributed to the compositional disorder of Ca 2+ and Y 3+ in the host lattice.