ESR study of Cr3+ in Naβ-alumina

The structure of impurity ions incorporated in the conducting plane of superionic conduction has been analyzed by ESR-Spectroscopy. The chromium centers have been identified to be quartet (S=3/2) states with |D|=(0.5±0.1) cm^–1 andE/D=0.13±0.01. Due to the crystal symmetry the spectra are reduced to only one single location of the Cr³⁺-ions, which is interpreted to be an anti-Beevers Ross lattice site.     

三斜相GdBO3:Eu的溶胶-凝胶法制备及其格位选择激发下的光谱

用溶胶－凝胶法合成了具有三斜结构的低温相GdBO3,并与用常规的固相反应制备球方解石结构的样品作了比较。在高于1000℃时发生了三斜相向常规相的相变。三斜相GdBO3:Eu的荧光光谱表明阳离子在基质晶格中占据了两种格位,用A和B来分别标明。选择激发A、B格位上Eu^3＋,结果揭示了GdBO3结构上的变化和Eu^3+之间的能量传递过程。在较高的Eu^3+掺杂浓度时,两上格位均有较强的发光;在低温和低浓度条件下,得到了可分辨的相应于不同格位的发光,并观察到了两个格位间的不同几率的能量相互传递。     

Luminescence characteristics of the Pr3+ ion in SrAlF5

The paper reports on a study of luminescence and excitation spectra of SrAlF₅:Pr³⁺ (0.5 mol %) polycrystals performed at 10 and 300 K with synchrotron radiation in the range from 5 to 25 eV. The Pr³⁺ ions in SrAlF₅ were shown to emit successively two photons in transitions from the ¹ S ₀ and ³ P ₀ levels. The main energy characteristics of the compound, namely, the position of the 4f → 5d excitation band (5.95–8.0 eV), the energy separation between the ¹ S ₀, 4f and the lowest 5d levels (～0.15 eV), and the SrAlF₅ band gap width (～12 eV), were determined. SrAlF₅:Pr³⁺ was found to possess a number of features not found in other Pr³⁺-activated fluorides.     

Site partitioning of Cr3+ in the trichroic alexandrite BeAl2O4:Cr3+ crystal: contribution from x-ray absorption spectroscopy

X-ray absorption spectroscopy measurements at the Cr K-edge of a trichroic crystal of alexandrite BeAl(2)O(4):Cr(3+) for different orientations of the crystal with respect to the polarization and direction of the x-ray incident beam have been performed. Analysis of the experimental spectra with the help of first-principles calculations of x-ray absorption spectra allowed us to estimate the proportion of chromium Cr(3+) cations among the two different octahedral sites of the alexandrite structure (70% in the C(s) site-30% in the C(i) site). The methodology presented in this work opens up new possibilities in the field of mineralogy for the study of complex minerals containing several sites potentially occupied by several transition elements or for solid solutions.     

Optical line narrowing by nuclear spin decoupling in Pr3+: LaF3

We have applied the technique of nuclear spin decoupling to the optical regime. In these experiments we selectively eliminated the role of ¹⁹F spin fluctuations as the dominant source of dephasing in the 5925A (¹D₂ / ³H₄)Pr³⁺ optical transition in 0.05% Pr³⁺: LaF₃ at 2K. The homogeneous optical linewidth (FWHM), measured by photon echoes, was reduced from 56 kHz to 6 kHz by on-resonance nutation of ¹⁹F in an external magnetic field of 375G. Further reduction of the linewidth to 4.1 kHz was observed by off-resonance irradiation of the fluorines such that their effective field in the rotating frame was at the ‘magic angle’ ($\text{cos}{}^{-1}\text{1}\text{3}$) with respect to the external field.     

Luminescence of Ce3+ ion in aluminate based phosphors for scintillator

Ce³⁺ activated aluminate based phosphors prepared by combustion synthesis are reported here. The emission of Ce³⁺ ion is observed around 321–354 nm in the ultraviolet region of the spectrum. The intensity of strong photoluminescence emission peak of Ce³⁺ ion increases when Mg is added to CaAl₁₂O₁₉ phosphor. The Ce³⁺ emission in CaAl₁₂O₁₉:Ce,Mg phosphor may be useful for scintillation application.     

Temperature dependence of the spectral line shift of MgO:Cr3+

The temperature dependence of the position of a spectral line MgO:Cr³⁺ is interpreted in terms of the Van Vleck orbit-lattice interaction appropriate for all phonon wavevectors.     

Absorption and fluorescence of Nd3+ ion in lanthanum-borate glass

The optical properties of lanthanum-borate glass having the composition B₂O₃.La₂O₃.SrO. BaO.ThO₂ with the addition of neodymium, i.e. their absorption and infra-red emission, luminescence decay and quantum yield, were measured. A study was also made of the concentration quenching of luminescence, the optimum concentration for use in a laser and the influence of the composition of the glass (content of thorium and exchange of bivalent ion). Compared with silicate glasses, these borates exhibit higher absorption, a lower quantum yield and decay that is an order of magnitude shorter. Of the chemical composition, only the thorium content plays a role.The paper follows on from an analogical paper on silicate glasses (Phys. Stat. Sol.9 (1965), 525) and measurements on a series of lithium-calcium-borate glasses are being prepared.     

Spectral line intensities of Yb3+ ion in LiNbO3 crystals

Optical spectra of absorption and luminescence of LiNbO₃:Yb³⁺ crystals are investigated experimentally and theoretically. Within the framework of the point charge approximation of crystal field, the Stark problem is solved: crystal field parameters and wave functions of Stark states are determined. Line strengths due to indirect electric-dipole and magnetic-dipole inter-Stark transitions are calculated and values of the Judd-Ofelt parameters are determined. Values of the branching ratios of luminescence. Einstein coefficients and, lifetime of the excited sublevel are calculated. A satisfactory agreement of calculated results with experimental data is obtained.     

Optical spectroscopy of Cr3+ and Cr3+-Tm3+ in alkaline silicate glasses

Conclusions Alkaline silicate glasses seem to be good candidates as host materials for codoping with Cr³⁺ and Tm³⁺. Cr³⁺ ions occupy mainly low-field sites in them, and their broadband emission overlaps Tm³⁺ excitation. As a consequence very high efficiency for the energy transfer Cr³⁺→Tm³⁺ is achieved with moderate concentrations of these ions. Moreover, the average lifetime of the Cr³⁺ ions in codoped glasses is long enough to allow significant energy storage by flashlamp pumping. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 62, No. 5, pp. 115–120, September–October, 1995.     

Electron-phonon and vibronic couplings in the FMO bacteriochlorophyll a antenna complex studied by difference fluorescence line narrowing

The electron-phonon and vibronic couplings governing the spectral properties have been studied in the Fenna-Matthews-Olson (FMO) bacteriochlorophyll a (BChl a)-protein complex at 4.5 K using a spectrally selective difference fluorescence line-narrowing technique. The complex is a part of the light-harvesting system of green photosynthetic bacteria. Its lowest-energy absorption band, peaking at 826 nm and responsible for the fluorescence, is believed to be due to Q_y transitions of largely isolated molecules. One of the main merits of the used method compared with the more common fluorescence line narrowing is that the zero-phonon lines (ZPL) resonant with the excitation laser can be accurately measured, allowing precise determination of the Huang-Rhys (HR) factors, the main characteristics of the linear electron-phonon and vibronic coupling strengths. Over 60 individual vibrational modes of intra- and intermolecular origin have been resolved in the energy range of 45-1600 cm⁻¹. The small HR factors for these modes, ranging between 0.001 and 0.018, add up to a value of S_vib=0.38±0.07. The effective HR factor for the phonons, S_ph, was found clearly wavelength-dependent, varying from ∼0.7 at short wavelengths to ∼0.3 at the long-wavelength tail of the absorption spectrum. Coupling between the BChl a molecules is likely responsible for this wavelength dependence.