J. Sokolnicki

Optical properties of Eu(III) chelates trapped in silica gel glasses

Abstract Preparation and optical properties of silica gel glasses doped with Eu(III) chelates (the complexes of β-diketones) are described. In particular the emission and excitation spectra of the precursor salts and glasses are reported. The assignment of electronic levels was proposed and the intensity analysis of the f–f transitions was performed. The decay times of 5D0 levels of Eu(III) complexes in gels are analyzed and compared with those reported for precursor salts.

Optical spectroscopy of the adducts of europium tris(dipivaloylmethanate) with derivatives of 1,10-phenanthroline

Abstract Spectroscopic investigations of the mutual influence of inequivalent ligands were undertaken using complex adducts of europium tris(dipyvaloylmethanate) with derivatives of 1,10-phenanthroline, Eu(DPM)3·Ph. The choice of a series of related Eu(DPM)3·Ph compounds provided the opportunity to study the dependence of the spectroscopic characteristics on the value of the effective charges at the atoms in the nearest surroundings of Eu3+ which, in turn, depends on steric factors and the donor–acceptor properties of the ligands. It was shown that steric factors are as significant as donor–acceptor properties of the ligands in the creation of the complexes. The changes in the strength and symmetry of the crystal field were evaluated from the Stark splittings of the Eu3+ transitions in luminescence spectra. Crystal field parameters were calculated. Two subgroups of compounds with similar spectra were distinguished. The relative efficiency of the excitation of Eu3+ luminescence through the ligand absorption bands and the relative luminance of the compounds were investigated. Changes of the ligand vibration frequencies and the strength of the electron–phonon interaction with various ligands were studied by IR and vibronic spectra.

Optical properties of Pr3+ in lanthanum double molybdates and tungstates: KLa1−xPrx(MO4)2 (M=Mo, W; x≤1)

Abstract Absorption, emission and excitation spectra of diluted single crystals of KLa1−xPrx(MO4)2 (M=Mo, W; x≤1) were measured. The intensities of the electronic transitions were analysed and related to the data of pure compounds. The fine structure of the electronic levels appearing in the optical spectra of the crystals is discussed. The temperature and concentration effects on intensities and the shapes of the observed bands are considered. Distinct vibronic sidebands were observed in the absorption, emission and excitation spectra for both systems. An assignment of the vibronic transitions is proposed and the single ion relaxation processes and the cooperative interaction are discussed.

Vibronic spectra and details of the structure of europium nitrates with derivatives of 1,10-phenanthroline

Abstract Luminescence and excitation of luminescence vibronic spectra as well as IR and Raman spectra of europium nitrates with 1,10-phenanthroline derivatives of formula Eu(NO 3 ) 3 .Ph 2 were studied. The effect of size of ligands and their effective charges on crystal structure and, as a consequence, on spectroscopic characteristics was investigated under conditions where one type of ligand (NO 3 − group) is sufficiently rigid. The second ligand, heterocyclic diimine, can change its size and donor-acceptor properties when the substituents are varied. Stark splittings and relative intensities of the Eu 3+ electronic transitions, the behaviour of vibration frequencies, and vibronic interaction were studied. It was demonstrated that nitrates under investigation have identical composition but form two different structural groups with small and bulky phenanthroline derivatives due to the influence of steric factor. All nitrate anions in the compounds are coordinated and the Eu-O (NO 3 − ) bonds are relatively strong. The values of the splitting of stretching vibrations of the NO 3 − -anions (▵= ν 4 − ν 1 ) and position of the band of ν (Eu–O) vibration show that the strongest Eu–O bonds are formed in Eu(NO 3 ) 3 .Nphen 2 , Eu(NO 3 ) 3 .Tmphen 2 and Eu(NO 3 ) 3 .Dphphen 2 due to high acceptor properties of nitro-phenanthroline and large size of tetramethyl- and diphenyl-phenanthroline molecules. Weak vibronic mixing of electronic and vibronic states was demonstrated in the region of 5 D 0 – 7 F 2 transition of Eu 3+ . The vibronic satellites of 5 D 0 – 7 F 0 -transition due to vibrations of the NO 3 − -group borrow about 1–2% of the intensity of the electric-dipole 5 D 0 – 7 F 2 transition yielding the increase of their relative intensity of 100 times in the Stokes sideband.

Fluorescence and Absorption Probe of Metal Ion Centers in Silicates Obtained by the Sol-Gel Technique

An optical probe of the structure of metal ion centers in sol-gel systems based on Eu3+ and Nd3+ emission and absorption measurements has been developed. The effects of the structure and composition of organic complexes of Eu3+ on the clustering processes and retention of water molecules in the gel and glasses were investigated. Mechanical properties of systems prepared with Triton detergent were also investigated. The studies have been performed for two types of complexes of lanthanides, with β-diketones as the precursor lanthanide salts. The emission, excitation and absorption spectra of the precursor salts, gels and glasses heated to 1100 K were measured. Splitting of the levels and electronic transition probabilities were analyzed. The IR spectra were used for the detection of the OH− modes in the glasses.

Comparative optical studies of lanthanide complexes with three types of phosphoro-azo derivatives of β-diketones

Abstract A new class of lanthanide compounds of the formula Na[LnL4]·H2O and LnC3·2H2O (where L=Wo or Az; Wo=CCl3C(O)NP(O)(OCH3)2; Az=C6H5C(O)NP(O)[N(CH2)2]2; C=CCl3C(O)NP(O)(NHC6H5)2) was obtained from mixed solvent solutions with the three types of phosphoro-azo derivatives of the β-diketones. Spectroscopic properties of these complexes are investigated and related to the structure and single crystal spectra of one of the above mentioned compounds [Amirkhanow et al., J. Appl. Spectr. 62 (1995) 5; Amirkhanow et al., Acta Phys. Polonica 90 (1996) 455]. The strong interaction of the ligands with the lanthanides was confirmed both by IR and electronic spectra. The intensities and splitting pattern of the electronic levels were used for the structure determination. IR and Raman spectra in the FIR and MIR regions have been recorded for solid lanthanide(III) (Eu, Pr, Nd) complexes with phosphoro-azo-β-diketones (Wo, Az and C). The normal coordinate analysis and potential energy distribution were performed for Ln(NPC2O4) molecular system consisting four chelate rings. On that basis, the assignment of the bands observed is proposed and related to the crystal structure of the complexes studied.

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.

Spectroscopic and magnetic studies of the ternary praseodymium chloride K2PrCl5

The optical and magnetic properties of K 2 PrCl 5 were investigated in the 1.7-293 K temperature range and are discussed on the basis of the X-ray crystal structure data. High-resolution absorption, emission, and excitation spectra as well as decay time measurements at 293, 77, and 4 K are presented and used to characterize the excited state photophysics of K 2 PrCl 5 . Magnetic susceptibility measurements were carried out down to 1.7 K in both the low and high field regime. Changes in the magnetic moment with temperature are discussed on the basis of the structural data. Spectroscopy and magnetism of K 2 PrCl 5 are related to respective results of other polynuclear and heteronuclear polymeric systems and are correlated with their EPR data.

Chirality effect on spectroscopy of dimeric lanthanide single crystals

Abstract Two series of Pr and Eu dimeric single crystals with l - and dl -isoleucine were obtained. The effect of the ligand chirality on the structure of the dimeric units was investigated. Well-resolved absorption, excitation and luminescence measurements on single crystals of these compounds as well as diluted systems down to 5 K are reported and analysed. Cooperative interaction is considered and vibronic lines are assigned based on vibrational analysis. The nature of the cooperative interaction in the praseodymium single crystals is briefly discussed.

Optical properties of Nd3+ in silica ceramics obtained by the sol–gel method

Abstract Heavily densified Nd 3+ doped silica ceramics were obtained by two different sol–gel based methods using distinct pH during gelation. The sample obtained at the higher pH showed more efficient emission. The morphology of the samples obtained was determined. It was found that Nd 3+ ions form nanosize as well amorphous aggregates. The optical properties of Nd 3+ doped silica ceramics were investigated.