R. Cases

Optical properties and cross relaxation among Sm3+ ions in fluorzincate glasses

Optical absorption and emission spectra are presented for Sm3+ ions in ZnF2−CdF2-based glasses (0.1, 1.5 and 2.5 mol% of Sm3+). The measured oscillator strengths and branching ratios for several transitions are compared with values obtained with The Judd-Ofelt theory. Energy transfer among Sm3+ ions has been investigated. The decay curves are nonexponential when the concentration is 1.5 or 2.5 mol%. It can be explained by cross relaxation between ions of Sm3+. Energy migration does not play a relevant role in these decay processes.

Infrared to visible upconversion of Er3+ ions in Yb3+ doped fluorohafnate glasses

The upconversion of infrared radiation into green and red luminescence has been studied for Er3+ and Yb3+ ions in fluorohafnate glasses. At room temperature normalized upconversion efficiency of 8.4x10-4 cm2/W has been obtained for the green emission (545 nm) of Er3+ in doped samples containing 4.5 mol% (Yb3+) and 0.75 mol% (Er3+) pumped by 974 nm light with an absorbed intensity of 2.5 mW/cm2. Both green and red upconversion radiations slightly decrease with increasing temperature. Room-temperature measured efficiency is compared with the calculated one obtained from the rate equation model of Wright.

Optical properties of Gd3+ in fluorozirconate glasses

Abstract Optical absorption and emission spectra of Gd 3+ ions in fluorozirconate glasses with two different compositions (ZBLA and ZBLALi) have been measured. Using the Judd-Ofelt (JO) theory and the experimental oscillator strengths of the absorption bands, JO parameters have been obtained for Gd 3+ which result to be the same for both hosts. These parameters are compared with those for other trivalent rare earth ions in the same glasses. Emission from 6 D, 6 I and 6 P terms have been detected and the lifetime of the 6 P 7 2 and 6 I 7 2 levels have been measured. These results, together with the radiative emission probabilities calculated from the JO parameters, allow us to give an estimate of the multiphonon relaxation rates which are discussed on the basis of the phenomenological gap law previously derived from Ho 3+ and Er 3+ data.

Spectroscopy of chromium (III) in yttrium-stabilized ZrO2

Abstract Chromium-doped yttria-stabilized zirconia (YSZ) single crystals were investigated using EPR, optical absorption, photoemission and emission lifetime techniques at temperatures between 8 and 300 K. A trigonal EPR signal is associated with the Cr 3+ ions. The hyperfine splitting with 53 Cr is about 44 MHz. The lineshapes and their dependence on the magnetic field orientation are explained by the presence of a Gaussian distribution of rhombic distortions. The optical properties are typical of a Cr 3+ ion in a six-fold coordination. The emission is dominated by the broad 4 T 2 fluorescence but at 8 K the R -emission is detected. The emission bands are inhomogeneously broadened and their intensities and lifetimes decrease as the temperature increases. We propose that Cr 3+ enters the lattice in a cation substitutional position whose environment has been distorted by a static Jahn-Teller effect. The local disorder of the YSZ lattice is responsible for the inhomogeneous broadening of the resonance lines.

Optical properties of ZnF2CdF2 glasses doped with 4f ions

Abstract Glasses with composition (in mol %), 32 ZnF 2 , 28 CdF 2 , 20 BaF 2 , 11 LiF, 5 AlF 3 , 4 LaF 3 have been prepared and doped with some 4f ions (Ho 3+ , Tm 3+ , Er 3+ ). The energy levels and oscillator strengths of the electronic transitions have been obtained. Using the Judd-Ofelt theory, the radiative transition probabilities between the different levels were calculated. We have measured the emission bands and lifetimes and determined the non-radiative transition rates, the luminescence efficiencies and the emission cross-sections of some “laser transitions”. The optical properties of this new material are slightly improved with respect to those of the fluorozirconate glasses.

Optical properties of Mn2+ ions in solid solutions of fluorite-type crystals

Abstract The optical properties of Mn2+ ions in Ca1−xSrxF2 and Sr1−xBaxF2 solid solutions have been studied. The positions of the excitation bands corresponding to electronic transitions from the 6A1g(6S) ground state of Mn2+ to different excited states as well as the luminescence emission which corresponds to the 4T1g (4G)→ 6A1g(6S) transition, change with the composition of the matrix. These changes have been qualitatively explained in a configurational coordinate model using the Tanabe–Sugano diagram for a d5 ion in a cubal environment and assuming that there is an increase of the electron–lattice interaction in the mixed crystals with respect to the unmixed ones. The thermal quenching of the photoluminescence has also been studied. The quenching temperature decreases in an almost linear way when the lattice parameter increases. This can be understood assuming that the electron–lattice interaction of the emitting level 4T1g is different from that of the ground state 6A1g.

Electron and hole trapped defects produced by thermoreduction or irradiation in Stabilized Zirconia

Abstract When undoped Yttrium Stabilized Zirconia is exposed either to reducing atmospheres or to electrical currents it becomes coloured. In this paper we present the results of a systematic study applying optical and EPR techniques to zirconia single crystals stabilized by calcium or yttrium, in which defects were produced by several methods including X-irradiation or reduction at different temperatures. Two EPR signals and three absorption bands have been related with three defects involving holes trapped in oxygen ions and electrons trapped in zirconium ions. The photothermal stability of the defects has been studied. Taking into account their spectroscopical properties and statistical considerations we propose novel models for these defects.

Phonon structure of Cr3+ photoluminescence in chromium doped MAF3 (M = Cd, Ca; A = Rb, Cs) crystals

Abstract The structure of the luminescence band of Cr3+ ions in CsCaF3, CsCdF3, RbCaF3 and RbCdF3 has been measured and analyzed using decay time measurements and time-resolved spectroscopy. The observed emission corresponds, in cubic Cr3+ centers, to the transition from the lowest spin-orbit (SO) component of the 4T2g(4F) level to the 4A2g(4F) ground state. The structure has been associated with the zero phonon lines (ZPL) and vibrational replicas of several types of Cr3+ centers, mainly cubic and trigonal ones. Four different phonon modes have been found in each of the crystals. Their frequencies change with the host crystal but not with Cr3+ symmetry. A tentative assignment of these phonon frequencies to normal modes of the [CrF6]3− complex has been proposed and discussed. The Cs compounds show a satellite at 14 cm−1 in the high energy side of each of the lines. It has been associated with the emission from the next SO component of the 4T2g level. The strong reduction of the SO coupling constant with respect to the free ion value is likely due to a dynamic Jahn-Teller effect.

Time resolved spectroscopy of Ni2+ doped fluoroclorozirconate glasses

Abstract Optical absorption, time resolved luminescence and fluorescence decay measurements of Ni2+-doped fluoroclorozirconate glasses are reported. Time resolved luminescence measurements were taken exciting the samples at different wavelengths. The position of the orange emission band (1T2g(D) → 3A2g(F)) moves to the blue when the excitation is changed to higher energies. For a fixed excitation wavelength, the emission moves also to the blue when the time of measurement after the laser pulse increases. The fluorescence decays are non-exponential and depend of the detection wavelength. They are slower for the shorter detection wavelengths. The results show a distribution of Ni2+ sites with different ‘crystal field’ environments.

Photoluminescence of Ti3+ in phosphate glasses

Abstract A Ti3+ infrared emission centered at 860 nm has been detected for the first time in inorganic glasses under excitation in the T2g → Eg transition of this ion. The optical properties (absorption and luminescence) of this system are studied and compared with those of the Al2O3:Ti3+, a recently developed tunable solid state laser material.