Single fluorescence centers on the tips of crystal needles: First observation and prospects for application in scanning one-atom fluorescence microscopy

A scanning optical fluorescence microscope is suggested, whose active element (needle) is made of a crystal containing impurity ions or color centers subject to excitation by laser radiation. The excitation energy from a single impurity center at the very tip of the needle is transferred by the resonance dipole-dipole exchange mechanism to fluorescence centers on the surface of the sample under study. It is demonstrated that this approach can help attain a nanometer-high spatial resolution at a high sensitivity substantially exceeding in some cases the sensitivity of the standard near-field fluorescence microscopy technique. Various crystals and impurity centers, potentially most suitable for the implementation of the method under consideration, are briefly analyzed. Information is presented on the manufacture of sharp-pointed needles from LiF crystals containing F₂-centers and the first observation of single F₂-centers on their tips by the laser-photoelectron projection microscopy technique, which allows one to speak of the practical creation of the first active elements for the microscope suggested.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Dynamics of Trp Residues in Crystals of Human α1-Acid Glycoprotein (Orosomucoid) Followed by Red-Edge Excitation Spectra

The present work reports for the first time the development of a method that allowed us to obtain crystals of orosomucoid complexed to progesterone. Then we investigated the dynamics of the microenvironments of the two buried Trp residues in the crystals of protein, by the red-edge excitation spectra method. The fluorescence excitation spectrum of the crystals is characteristic of that known for Trp residues (_max = 290 nm and bandwidth = 38 ± 1 nm), indicating that the Trp residues are responsible for the fluorescence of the protein in the crystals. The position of the maximum and the bandwidth of the steady-state emission spectrum of the crystals (331 ± 1 and 43 ± 1 nm, respectively) are equal to those obtained in aqueous buffer for the orosomucoid–progesterone complex (330 ± 1 and 43 ± 1 nm) (_ex, 295 nm). Thus, the fluorescence of the crystals occurs from the Trp residues buried in the protein core. The red-edge excitation spectra studies indicate that the Trp residues are surrounded by microenvironments that display motions, a result identical to that observed in solution. Thus, the crystallization process does not modify the structure or the dynamics of orosomucoid core. The fluorescence intensities depend on the angular orientation of the crystals with respect to the polarization of the incident beam. The general feature of this dependence is identical at the three excitation wavelengths used (295, 300, and 305 nm). Our results confirm the fact that the local structure and dynamics are the key for any interpretation of tryptophan fluorescence parameters of orosomucoid.     

Triple Fluorescence of Substituted Benzanilides in Solution and in Solid States

The competitive triple fluorescence of benzanilide is studied by steady-state fluorescence investigations in dependence on the solvent polarity and the para-substitution of the aniline core as well as by comparison with the fluorescence behavior of 4-methoxy-N-methylbenzanilide. The normal fluorescence of benzanilide S₁(LE) S₀ appears at _max = 345 nm, whereas a superposition of proton transfer (PT) fluorescence S₁(PT) S₀(PT) and intramolecular charge transfer (ICT) flu-orescence S₁(ICT) S₀(FC) is responsible for the long-wavelength fluorescence in the 500-nm region. Different possibilities for the formation of the PT and ICT states are discussed. Investigations of the fluorescence behavior of benzanilides both in solution and as crystals in dependence on the para-substitution of the benzanilide moiety support the PT/ICT model.     

Low-temperature luminescence of silicon carbide crystals

The high-energy part of the blue fluorescence of-SiC(6H) is found to be dependent on the nitrogen (donor) concentration. The line fluorescence spectrum is found to include a new series of lines due to radiative transitions to A1 acceptor levels.We are indebted to J.G. Pichugin for providing the crystals.     

Effects of co-dopant concentrations and excitation conditions on the 2 μm fluorescence dynamics in Tm,Ho:YLF crystals

Results of spectroscopic studies carried out on Tm, Ho:YLF crystals are reported. In particular, we have investigated the effects of the co-dopant concentrations on the time evolution of the fluorescence at 2 m emitted in response to short-pulse laser excitation at 792 nm. The fluorescence intensity profiles are analyzed in terms of their temporal and amplitude characteristics over a wide range of excitation conditions.     

Identification of trace impurities in pure and doped YAlO3 and Y3Al5O12 crystals by their fluorescence and by the EMA method

Trace uncontrolled impurities as Ce³⁺, Cr³⁺, Eu³⁺ and Nd³⁺ were detected in YAlO₃ and YAlO₃: Cr crystals from their fluorescence by high sensitive photon counting detection. The concentrations of Ce, Cr, Eu, Nd and some other impurities (Tm, Ho, Mn, Mg, Fe) were also determined by electron beam excited X-ray microanalysis (abbr. EMA) in YAlO₃ and Y₃Al₅O₁₂ crystals (pure or doped). Both the methods (fluorescence detection and EMA) are compared, fluorescence properties of some trace impurities were determined and their influence on local distribution and transfer processes (Ce³⁺Nd³⁺, Cr³⁺ Nd³⁺) in these crystals are discussed.The authors are grateful to J. Kvapil, Jos. Kvapil and K. Blaek from Preciosa a.s., Division Monokrystaly, Turnov, Czech Republic, for supplying us with YAlO₃ and Y₃Al₅O₁₂ single crystals.     

Szintillationseigenschaften dotierter organischer Molekül-Einkristalle bei Beschüß mit α-Teilchen

Scintillation anisotropy of organic crystals containing impurities was measured. Single crystals oft-stilben with impurities of anthracene and naphthacene and single crystals ofp-terphenyl containing anthracene were bombarded withα-particles in order to investigate their scintillation response as function of direction ofα-particles and concentration of guest molecules. The relations between the results and the polarization of the fluorescence light of the corresponding molecules are discussed.     

Quantum correlated twin beams

We discuss recent progress in the study of the non-classical properties of light beams generated by non-degenerate parametric splitting in ⁽²⁾ nonlinear birefringent crystals, with special emphasis on their quantum correlation (twin beams). We describe experimental results using successively pure parametric fluorescence, parametric amplification of a weak signal beam pumped by a pulsed laser, and parametric oscillation in a cavity pumped by a cw laser. In this review, we compare the respective advantages and drawbacks of the different approaches.     

Some physical properties of ZnS crystals grown from the vapour phase

Wurtzite-type crystals with wide regions of high purity and good optical properties have been grown in a few hours by an improved flow method. Dislocations have been found to be mainly arranged inside isolated striation regions where a weak green fluorescence and phosphorescence has been observed. Under bending deformation the crystals show a plastic behaviour that is not directly correlated to the mean dislocation density of the samples. Rupture has been found at about 10³ kg/cm².The microwave method for the detection of crystal deflection has been suggested by Prof. A. Gozzini. His helpful advice and interest in this research has been deeply appreciated. Many thanks are also due to the Physical Institute of SAV in Prague, for the possibility to work on their crystals of ZnS. Finally we wish to thank Mr. Coli and Mr. Montanari for design and construction of the mechanical equipment and the furnace quartz assembly.     

The photodielectric effect in ZnS-Cu monocrystals

The frequency dependence of the photodielectric effect, transition-process kinetics, and peculiarities of IR light action on tan are studied. It is shown that a photodielectric effect of the first type occurs not only in ZnS-Ag crystals but also in ZnS-Cu crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 40–43, January, 1976.     

Cooperative emission of photons by weakly coupled chromium ions in Al2O3

Under strongcw-excitation ruby crystals exhibit complex anti-Stokes fluorescence spectra in the near ultraviolet. Based on ring dye laser excitation spectra, fluorescence decay and concentration dependence, we show that these spectra can be decomposed into single ion emissions and a cooperative emission at the double energy of the² E⁴ A ₂ transition. The unusual vibronic sideband of the latter suggests a general mechanism for the coupling of distant ions in polar insulators involving the electric field of longitudinal optical phonons.Work supported by Sonderforschungsbereich 65 Frankfurt/Darmstadt     

Zur Frage der Pb(II)-Komplexe in Gemischten KCl-KBr-Kristallen

The absorption and fluorescent spectra of mixed KCl-KBr crystals with lead admixtures were measured. A comparison with the absorption of analogical mixed solutions showed that the displacement of the absorption band of lead towards longer wave-lengths with increasing content of bromide is caused by the creation of mixed complexes. The latter are also responsible for the fluorescence of the crystals.

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Die Verfasser danken herzlich Herrn Dr. A. Bohun für die wertvollen Diskussionen. Sie danken ferner Frau K. Dolealová für die Durchführung der Absorptionsmessungen der Kristalle und Frau M. Kubovská für die Züchtung der Kristalle.     

Optical properties of Ni-doped single crystals grown by floating zone method

The single crystal growth conditions and spectroscopic characterization of Ni-doped MgGa₂O₄ with inverse-spinel structure crystal family are described. Single crystals of this material have been grown by floating zone method. Ni-doped MgGa₂O₄ single crystals have broadband fluorescence in the 1100–1600 nm wavelength range, 1.6 ms room temperature lifetime, 56% quantum efficiency and stimulated emission cross section at the emission peak. This new material is very promising for tunable laser applications covering the important optical communication and eye safe wavelength region.     

Antiphase domain boundaries in silicon-iron alloys

A new technique has been developed for the observation of antiphase domain boundaries. The APB's are etched electrolytically in chromium trioxide water solution on the surface of bulk single crystals of silicon iron alloys. The APB's in crystals of iron with silicon content from 9·5 to 21 at.% are studied. Two types of thermal APB's are observed. The first type observed in crystals with silicon content up to 12·5 at.% is crystallographically independent; the second type observed in crystals with higher silicon content shows tendency to lie in {100} planes. The dependence of domain size on the silicon content is determined. In addition to the thermal APB's nonthermal APB's are observed. They were left behind the dislocations which moved due to thermal stresses. The interaction between the thermal and nonthermal APB's is studied.The author is indebted to Mrs. Kadeková for the preparation of the silicon iron single crystals and wishes to express his thanks to F. Kroupa, B. esták and A. Gemperle for their valuable discussions.     

Impurity Luminescence of Alexandrite Crystals

The luminescence of alexandrite excited by a highcurrent electron beam is investigated. Its spectrum has bands of the impurity ions Cr³⁺ and of the Cr–Cr pairs and also the band at = 492–495 nm. In all of the crystals we have detected chromium ions distributed over two nonequivalent positions, differently in different crystals. It is shown that the color of the crystals and its change on illumination of the crystals with the light of different spectral composition depend mainly on the chromium ions and their distribution over crystalline positions. A noticeable effect of other impurity ions is noted for a number of crystals.     

Infrared radiation of zinc selenide single crystals

Long-wave photoluminescence (PL) spectra of both as-grown and Au-doped n-ZnSe single crystals are studied in the temperature range from 81 to 300 K. A narrow band of infrared (IR) radiation centered at 878 nm (1.411 eV) manifests itself in the low-temperature PL spectrum. It is established that this band intensity first increases and then decreases with increasing concentration of doping impurity. With increasing excitation radiation intensity, spectral position of the IR PL band is unchanged and its intensity increases under the linear law. With increasing excitation radiation wavelength, the IR PL band intensity increases, it becomes narrower and shifts towards long wavelengths. It is shown that the observed IR radiation is caused by recombination of free electrons with holes localized on associative acceptors in the ZnSe:Zn:Au crystals or in the undoped crystals.     

Crystal growth rates of diblock copolymers in thin films: Influence of film thickness

Using optical and atomic force microscopy we determined the growth rate of polymer crystals in thin films of low molecular weight poly(styrene-ethyleneoxid) block copolymers. We focused in particular on films either thinner or slightly thicker than the thickness of a crystalline lamella (L). At a given temperature, three distinctly different growth rates were observed for i) crystals grown from adsorbed monolayers thinner than L, ii) primary compact lamellar crystals in films thicker than L and iii) secondary crystals formed from molecules remaining on top of ii). The growth rate of primary crystals did not indicate a dependence on film thickness. Crystals from monolayers grew by a factor of 30 more slowly than primary crystals. Secondary crystals grew faster than crystals from monolayers but slower than primary crystals and the degree of deviation from the growth rate of primary crystals was found to depend on the value of L, which varied with temperature. The mechanisms responsible for the differences in growth rate are discussed in terms of the amount of available polymers and the controlling influence of diffusion towards the crystal front.Received: 9 September 2003PACS: 61.41. + e Polymers, elastomers, and plastics - 68.47.Mn Polymer surfaces 68.55.-a Thin film structure and morphology - 81.10.Aj Theory and models of crystal growth; physics of crystal growth, crystal morphology and orientation     

Optical study of praseodymium doped yttrium aluminium garnet

The absorption and fluorescence spectra of YAG crystals doped with praseodymium at 1% level are investigated through dye laser spectroscopy. The spectra can be interpreted as evidence for at least three series of crystallographic sites for Pr³⁺, but only the transitions which involve the ground state are really complex, that is multi-sites like. It is suggested that an electronphonon interaction occurs through resonance with peaks in the density of phonon states and ground state Stark levels in the range 350–750 cm^–1. This creates new vibronic states and the appearance of a large number of lines for transitions involving ground state especially if laser excitation of the fluorescence is used.Presented at the International Symposium on Solid State Chemistry, October 28–31, 1986, Karlovy Vary, Czechoslovakia.     

Radiative electronic transitions in ZnTe∶Al,Ga, in crystals

We report the results of studies on the concentration dependence of the cathodoluminescence of ZnTe:Al, Ga, In crystals in the temperature range 4.2–300 K. A band with maximum at 2.2 eV and half-width of the order of 70 MeV and a band with maximum at 2.36 eV and half-width 1 MeV appear in ZnTe:Al crystals at 4.2 K. In the temperature range 40–70 K we detected the structure of the first band such that the separation of the maxima of the resolved bands corresponded to the energy of an LO phonon. A band with maximum at 1.8 eV was found to appear in ZnTe:Ga crystals at 4.2 K and a band with maximum at 1.9 eV appeared in ZnTe:In crystals at that temperature. The donor activation energies were determined to be 0.11, 0.30, and 0.25 eV, respectively, for aluminum, gallium, and indium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 82–86, October, 1987.