J. Chrysochoos

Fluorescence enhancement of Eu3+ by Tb3+ in dimethylsulfoxide (DMSO)

Abstract Photoexcitation of EuCl 3 .6H 2 O and TbCl 3 .6H 2 O mixtures in DMSO at various wavelengths brings about a decrease in the fluorescence intensity of Tb 3+ and a subsequent enhancement in the fluorescence intensity of Tb 3+ provided that [Tb 3+ ] 3+ ]. The average value of the electronic excitation energy transfer rate constant k 10 which was found to be independent of the excitation wavelength, was determined to be about 1.50 × 10 3 M -1 s -1 . Photoexcitation of Tb 3+ and subsequent population of high energy excited states is accompanied by rapid nonradiative de-excitation processes to the lowest excited state 5 D 4 , which is the origin of the energy transfer process. A lower limit for the value of the reaction rate constant, associated with the transition 5 D 3 ⇝ 5 D 4 , namely k 5 , is of the order of 10 5 −10 6 s -1 . Excitation at conditions leading to the exclusive population of the 5 D 4 state of Tb 3+ gave rise to a value of k 10 equal to (2.2 ± 0.4) × 10 3 M -1 s -1 and a critical separation ( R 0 ) exp between Tb 3+ and Eu 3+ of about 13 A. A theoretical value of R 0 equal to 14.2 A was calculated. The energy transfer process does not appear to take place via clear cut dipole-dipole interactions but rather via complex multipole and/or exchange interactions.

Electronic excitation energy transfer between Tb3+ and Eu3+ in DMSO

Abstract Excitation of Tb 3+ and Eu 3+ in DMSO with 487 mμ, which corresponds to the 7 F 6 → 5 D 4 transition of Tb 3+ , is accompanied by a reduction in the fluorescence efficiency of Tb 3+ as [Eu 3+ ] increases and by the appearance of a weak emission from Eu 3+ . An average rate constant for both the fluorescence quenching of Tb 3+ and the energy transfer from Tb 3+ to Eu 3+ with subsequent emission from the latter, was found to be (2.2 ± 0.4) × 10 3 M −1 sec −1 .

Concentration and temperature dependence of the lifetimes of the fluorescence arising from the second excited state of Tb3+ (5D3) in POCl3:SnCl4

Abstract Excitation of Tb 3− in POCl 3 :SnCl 4 (9/1 by volume) at wavelengths shorter than 487 ± 1 nm ( 7 F 6 → 5 D 4 ) is accompanied by fluorescence emission from both the 5 D 3 and 5 D 4 states of Tb 3+ . The fluorescence lifetimes of the former emission are shorter, namely τ ??? = 0.4 ms at 25°C and 1 × 10 −2 M Tb 3+ and they exhibit a dependence upon both the concentration of Tb 3+ and the temperature. This dependence is attributed to the depletion of the population of the 5 D 3 state by coupling the transitions 5 D 3 → 5 D 4 and 7 F 6 → 7 F 1 or 7 F 0 of Tb 3+ . This self-quenching process is slightly temperature dependent. An activation energy barrier of about 3 kcal/mole has been determined.

Dependence of the intensity of the absorption bands of Eu3+ in solution upon the anions present

The narrow and very weak absorption bands of Eu3+ in solution at 526 nm and 579 nm associated with the transitions 7F0 → 5D1 and 7F0 → 5D0, respectively, are accompanied by red‐shifted broad bands. The red shift depends upon the anion present and it is independent of the solvent. In the case of EuCl3 the red shift was found to be 335±2 cm−1 whereas in the case of Eu(NO3)3 a red shift of 366±2 cm−1 was observed. The intensity of the broad bands is solvent dependent and it increases as the dielectric constant of the solvent decreases. These bands are attributed to the nonionized rare‐earth salts, i.e., > Eu–Cl and/or > Eu–NO3. On the other hand, the intensity of the narrow band at 526 nm is almost unchanged despite the changes in the intensity of the broad band. Since the intensity of the band at 526 nm, which is associated with Eu3+, ought to decrease as the intensity of the broad band increases, the lack of change may be attributed to an enhancement of the appropriate oscillator strength due to vibronic e...

Effect of the primary and secondary solvation spheres of Eu3+ upon the electric-quadrupole transitions (ΔJ = 2)

Abstract Variations in the structure and nature of the primary solvation sphere of Eu 3+ are accompanied by pronounced effects upon the electric-quadrupole transitions of Eu 3+ associated with both absorption and emission bands, i.e., at 464–466 mμ ( 7 F 0 → 5 D 2 ) and 614–616 mμ ( 5 D 0 → 7 F 2 ). In cases in which the primary solvation sphere of Eu 3+ does not change, although the secondary sphere undergoes slight changes, small effects, if any, are observed upon both the appropriate absorption and emission bands. More drastic variations in the secondary solvation sphere are accompanied by weak, but clearly detectable, changes in the intensities of both bands.

Secondary fluorescence quenching of Eu3+ in organic solvents

Abstract The fluorescence of Eu 3+ in organic solvents is subject to quenching by the solvent molecules both in the solvation sphere of Eu 3+ and outside the primary solvation sphere of the complex ion. Quenching rate constants relating to the latter effect, k secondary solvent , vary from solvent to solvent. The normalized fluorescence of Eu 3+ in these solvents exhibits an inverse dependence upon the overlap between the fluorescence spectrum of Eu 3+ and the vibrational spectrum of the solvent.

Selective excitation and decay of the fluorescence emission arising from the 5D4 state of Tb3+ in POCl3:SnCl4

Light excitation of Tb3+ in POCl3:SnCl4 at 488±1 nm giving rise to direct population of the 5D4 state, is accompanied by fluorescence emission whose decay is a simple exponential. On the other hand, indirect population of the 5D4 state, via excitation with shorter wavelengths and relaxation of higher excited states of Tb3+, gives rise to fluorescence emission characterized by a very complex decay law. The nature of the complex decay and the conditions at which maximum fluorescence intensities are attained are discussed. The fluorescence lifetime of the 5D4 state, τ4, is independent of [Tb3+] but decreases slightly at higher temperatures. This is attributed to a temperature dependent quenching process of the 5D4 state of Tb3+ by the solvent.

Temperature and solvent effects upon the 5D35D4-transition of Tb3+ in POCl3:SnCl4

Abstract Excitation of Tb 3+ in POCl 3 :SnCl 4 with ultraviolet light gives rise to fluorescence emission arising from both the 5 D 3 and the 5 D 4 -states of Tb 3+ whose relative contribution is a function of both the composition of the solvent and the temperature at constant [Tb 3+ ]. The fluorescence lifetime of the light emitted via the transitions 5 D 3 → 7 F J (J = 0, 1, …, 6) increases at lower [POCl 3 ] [SnCl 4 ] -ratios and temperatures. The nonradiative process 5 D 3 → 5 D 4 is brought about via interactions between the excited Tb 3+ and POCl 3 molecules at very low [Tb 3+ ]. The activation energy barrier of the electronic excitation energy transfer from Tb 3+ to the solvent is 3.4 kcal/mole at [POCl 3 ] [SnCl 4 ] = 12.5 and increases slightly at higher ratios, to a maximum of 4.15 kcal/mole at [ POCl 3 ]/ [ SnCl 4 ] = 55.5.

Radiative and radiationless processes of Eu3+ in dimethyl sulfoxide

Abstract Solutions of Eu3+ in dimethyl sulfoxide (DMSO) exhibit a considerable enhancement in the intensities of bands associated with ▵J = 2 both in the absorption and in the emission spectra. This effect is so strong that addition of considerable amounts of either D2O or H2O has no effect at all. Contrary to that, addition of very small quantities of DMSO in solutions of Eu3+ in D2O is accompanied by drastic changes in the appropriate transition probabilities. In solutions of Eu3+ in DMSO containing relatively small [H2O] or [D2O], the primary solvation sphere appears to consist mainly of DMSO. Secondary and primary fluorescence quenching rate constants have been determined such as: ksecD2O ⩾ 5.1 M-1 s-1; ksecDMSO ⩾ 20 M-1 s-1 and kfl + k≈h ⩽ 4.5 × 102 s-1.

Pathways of Radiative and Nonradiative Transitions of Tb3+ in DMSO

Abstract Recent luminescence studies of Eu3+ in organic solvents and in aqueous solutions have revealed that the fluorescence efficiency of the rare-earth ion depends upon both the primary and the secondary solvation spheres of the ion. Primary and secondary fluorescence quenching rate constants of Eu3+ have been determined for various compounds such as CH3COOH, CF3COOH, CH3COCl(1) as well as for such specific groups as the ←C-H and -OH groups of CH3COOH(2). In these studies the primary solvation sphere of Eu3+ consisted mainly of CH3COOH i.e. [CH3COOH]/[EuCl3] = 17, whereas the second solvent or any excess of CH3COOH were located in the secondary solvation sphere. In cases in which the rare-earth salt was soluble in both solvents, such as in DMSO-H2O, D2O-ETOH, D2O-CH3COOD, DMSO-D2O or D2O-H2O, a gradually varying primary solvation sphere exhibited a paramount effect upon both the fluorescence efficiency and the transition mechanisms of Eu3+. A drastic effect due to traces of DMSO upon the 7Fo ←5D2 and 5...