W. Strȩk

Site selection spectroscopy of Cr3+ in MgAl2O4 green spinel

Abstract The optical properties of Cr3+ ions in the synthetic green spinel MgAl2O4 were re-examined by means of site selection spectroscopy. In particular, our attention was focused on the distribution of Cr3+ sites embedded in this disordered crystal. By means of site selection excitation spectroscopy, a number of Cr3+ classes associated with strong, intermediate and weak ligand field sites were identified. The fluorescence line narrowing technique was used to establish the 25 Cr3+ sites. The splitting of the 4A2 level was determined to be 1.7 cm−1. It was found that in higher concentrated samples the number of weak ligand field Cr3+ sites is increasing.

Optical properties of Pr3+ doped silica gel glasses obtained by sol–gel method

Abstract Thermally densified silica glasses doped with Pr3+ ions were prepared by sol–gel method. Three procedures of synthesis are described. Absorption, emission and excitation spectra of Pr3+ doped silica glasses obtained by sol–gel method are reported. We found on the basis of now presented results and those earlier reported that intensities of the absorption bands of Pr3+ change with concentration nonlinearly, especially in the range of 3H4→3P2; 3P0 and 1D2 transitions. This phenomenon could be caused by clustering, which leads to cooperative interactions. On the basis of the absorption spectra measurement, the energy level diagram was prepared which helps in the explanation of the emission properties of glasses synthesized by different techniques. The luminescence spectra were dependent on excitation wavelength. The spectra excited in high UV range exhibited, except emission in the red range corresponding to the 1D2→3H4 transition, a broad band emission with characteristic holes at the envelope corresponding to the 3P2, (3P1, 1I6) and 3P0 terms. Nature of this broad band emission is discussed. The observed holes result from reabsorption processes, which are controlled by concentration of active ions. Mechanism of their occurrence remains unknown. No emission from 3P0 level was observed for some kind of glasses, for another one the emission from 1D2 and 3P0 levels was detected.

Optical properties of Cr3+ in MgAl2O4 spinel

Abstract Absorption and luminescence spectra of Cr 3+ in the disordered synthetic MgAl 2 O 4 spinel are reported. The splitting of the 4 T 2g absorption band and the excitation wavelength dependence of luminescence indicate the presence of two different Cr 3+ sites in this crystal. An excitation of Cr 3+ in site A leads to broad band fluorescence whereas an excitation of the B site leads to the narrow band luminescence similar to that of the natural spinel. The nature of luminescence is discussed.

The nature of Cr(III) luminescence in MgAl2O4 spinel

Abstract The broad-band emission of Cr(III) in the MgAl2O4 synthetic spinel was observed. Following the absorption measurements and excitation wavelength dependence of luminescence spectra the nature of luminescence is combined with two different Cr(III) sites in this crystal. The temperature dependence of luminescence and the time resolved spectra indicate that the broad-band luminescence may be attributed to the 4T2 → 4A2 fluorescence.

Dynamics of energy transfer in Tb1-xEuxP5O14 crystals

Abstract The dynamics of donor-donor and donor-acceptor interactions was studied in the Tb 1- x Eu x P 5 O 14 crystals. It was found that the decay curves of the 5 D 4 emission show an exponential behaviour for the whole Eu 3+ concentration range at low temperature. Nonexponential decay was observed, however, for high Eu 3+ concentration at room temperature. The mechanism of energy transfer processes between Tb 3+ and Eu 3+ is discussed in terms of both the non-resonant and the anti-Stokes resonant cross relaxations contributing to the deactivation of the 5 D 4 state.

Spectroscopic and physicochemical properties of rare-earth phthalocyanines entrapped in sol-gel glasses

Abstract The electronic absorption spectra of samarium and neodymium phthalocyanines in DMSO and entrapped in glasses obtained via the sol-gel technique have been obtained. Decrease in concentration of metallophtalocyanines in DMSO leads to observed changes in the relative intensifies of the two bands in the Q-band region. This behavior could be explained by the shifts in equilibrium between the LnPc 2 and LnPc + forms, caused by the dilution. In view of this interpretation, the entrapment of the metallophthalocyanines in the sol-gel glass matrices shifts the diphthalocyanine ⇆ monophthalocyanine equilibrium towards the monophthalocyanine (LnPc + ) form.

Luminescence properties of U3+ doped chloride elpasolite

Abstract Absorption and luminescence spectra of U3+ in Cs2NaYCl6 single crystals are reported. An efficient luminescence is observed in the visible (centered at about 12282 cm−1 and 12903 cm−1) and near infrared (at 6321 cm−1 and 6940 cm−1) regions. Following the absorption spectra analysis, the luminescence bands observed in the visible and near infrared regions are assigned to the 4G 1 2 → 4I 9 2 and 4F 3 2 → 4I 9 2 transitions respectively. The observed emission bands are dominated by electric dipole vibronic transitions, for which an assignment is also proposed.

Absorption and luminescence spectra of dysprosium compound in non-aqueous solutions. Spectral intensity analysis.

Abstract Absorption and luminescence spectra of dysprosium compound were measured in non-aqueous solutions (alcohols, amides) within the region 5500 – 35000 cm−1. The oscillator strengths of the f-f absorption bands were determined. The intensities of the Dy+3 ground state absorption were analyzed based on the Judd-Ofelt theory. A polarizability effect on the intensity of f-f transition was considered. The quenching mechanism of luminescence of the 4F 9 2 level for Dy+3 ion in non-aqueous solutions was discussed.

Emission spectra of U3+ in Cs2NaYBr6

Abstract Absorption, Raman, infrared and emission spectra of U 3+ in Cs 2 NaYBr 6 are reported. The low-temperature emission spectra are characterized by a rich structure of vibronic transitions. Following the absorption transition data and the vibrational analysis, the assignment of the emission transitions is proposed.

Analysis of the 8S72 → 6PJ two-photon absorption transitions of Gd3+ in Cs2NaGdCl6

Abstract Measurements of the 8 S 7/2 → 6 P J , 6 I J two-photon transitions of Gd 3+ ions in the cubic elpasolite Cs 2 NaGdCl 6 are reported. The two-photon excitation spectra of the intense ultraviolet fluorescence exhibit two main features: (i) the predominance of the 8 S 7/2 → 6 P 7/2 lines, and (ii) the observation of the 6 P 3/2 and 6 I 7/2 states unobservable in one-photon absorption. Moreover, the two-photon transition intensities are well reproduced by extending the second order standard theory to include third order terms involving the spin-orbit interaction within the 4f 6 5d states. To this purpose we developed a crystal-field calculation that fit the experimental data quite well.