Furthermore, the object is achieved by a security feature according to the appended independent claim 8 , by security or value document according to the appended independent claim 9 and by a method of detecting a security feature in a security document according to the appended independent claim 10 degrees.
The phosphor according to the invention, preferably powdered, zinc sulfide in addition to its specific electroluminescence exhibits an intense and thus detectable by conventional sensors photoluminescence, which is further characterized by a characteristic color change on variation of the UV-excitation conditions.
Thus, the phosphor emits either blue or green photoluminescence. This is independent of the electroluminescent color change of UV-excitable photoluminescence can be utilized as an additional criterion of authenticity in the application of the phosphor according to the invention in security features. The exclusivity and complexity of the Lumineszenzverhaltens described is bound to a particular phosphor composition, which is given below. In any case, the phosphor basically comprises Cu as an activator. A is preferably exclusively for Cu.
M stands for Al, which may be partly replaced by one or more metals selected from the elements Bi, Ga and In comprehensive group. Das Al und ggf.
In any case, the phosphor basically comprises Al. Preferably M is exclusively for Al. X stands for one or more halides, as monovalent anions X - occur and are selected from the elements of F, Cl, Br and I group comprising. Die genauen Gitterpositionen, auf denen die Ionen von A, M und X eingebaut sind, lassen sich nicht bestimmen. The exact grid positions on which the ions of A, M and X are installed, can not be determined.
In dieser vereinfachten Schreibweise sind die Indizes a, b und c nicht angegeben. In this simplified notation, the indices a, b and c are not specified.
The simultaneous presence of copper and the two different types of co-activators in the zinc sulfide basic lattice is a requirement that at least always two different activatable radiation centers arise that can possibly be regarded as the cause of the surprisingly found specific luminescence properties of Elektroluminophors invention. The phosphor of the invention may include minor amounts of other elements, provided these do not impair its above characteristics and do not delete the emission intensities an unacceptable degree.
Praktische Versuche haben gezeigt, dass trotz intensiven Auswaschens im Endprodukt vereinzelt Alkali- bzw. Practical tests have shown that despite intense washing out in the final product alkali or alkaline earth elements are separated analytically detectable if they had been added in the form of their halides the approach scuffle. It can not yet clearly established whether these elements are incorporated into the basic mesh or whether they are present as non-leachable inclusions in the phosphor.
Somit stellt das Vorhandensein bzw. Fehlen von Alkali- bzw. Thus, the presence or absence of alkali metal or alkaline earth metal ions is not a feature which is beyond the present invention. A further subject of the invention is a method for producing a zinc sulfide phosphor, in particular the zinc sulfide phosphor of the invention. The method first comprises a step of providing the starting compounds. Main component of the reaction mixture is zinc sulfide ZnS , said base substance may be added optionally in addition certain amounts of sulfur S.
Bevorzugt wird elementarer Schwefel als ein weiterer Ausgangsstoff verwendet und mit den ggf. Ebenso wird eine Kupfer Cu enthaltende chemische Verbindung als Ausgangsstoff bereitgestellt.
Blue and white light emission from zinc oxide nanoforests
Similarly, a copper Cu containing chemical compound is provided as a starting material. The copper required for the synthesis of zinc sulfide invention Elektroluminophors as activator Cu as a rule as copper sulfate CuSO 4 is introduced into the mixture of Ausgansstoffe. Somit handelt es sich bei der das Kupfer umfassenden chemischen Verbindung bevorzugt um Kupfersulfat. Thus, it is preferred in the composition comprising the chemical compound of copper is copper sulfate. When the Ag-containing compound is preferably AgNO.
Wherein the Au-containing compound is preferably Na 3 [AuCl 4]. Im Weiteren wird eine Al enthaltende chemische Verbindung bereitgestellt. In addition, an Al-containing chemical compound is provided.
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This applies correspondingly also for the Bi-containing chemical compound containing the chemical compound and Ga for the In-containing chemical compound that can be used in addition. Weiterhin wird eine ein Halogenid X enthaltende chemische Verbindung bereitgestellt.
Further, a X is a halide-containing chemical compound is provided. The formula symbol X represents one or more elements selected from the elements of F, Cl, Br and I group comprising. The formula symbol X preferably represents I. The iodine I passes, as well as the other halides described in the general formula, usually in the form of the corresponding alkali metal e.
The Al, Bi, Ga or In-containing compound and the compound containing the halide X may be identical, for example. For example, as aluminum halide AlX3 or as bismuth halide BiX 3. Some of the provided as starting materials for carrying out the process chemical compounds can also act as a flux in the subsequent thermal treatment. Die bereitgestellten chemischen Verbindungen sind ggf. The chemical compounds are provided to ground if necessary. The present powdered chemical compounds are incorporated into one another to a mixture. According to the invention the annealing of the mixture in the presence of activated carbon, the presence of which plays an important role in the required for the production of the inventive phosphor setting the local annealing atmosphere is carried out.
As already mentioned, is instead important for the invention that a fine regulation of the local annealing atmosphere is possible by the presence of activated carbon. In an alternative preferred embodiment, the annealing under stagnant air takes place. The mass of the activated carbon present is preferably from 0. Die Aktivkohle ist bevorzugt in einer Graphitschale angeordnet, welche oberhalb der verdichteten Mischung angeordnet wird.
The activated carbon is preferably disposed in a graphite shell, which is arranged above the compressed mixture. The glow of the mixture preferably lasts at least two hours. The trained phosphor is then cool. It is then milled in accordance with an embodiment, washed, dried and sieved. In this simple case, the phosphor is then available without further necessary steps available.
Radiation Emitted by Optically Excited Zinc Vapor.
It has surprisingly shown that it may be for the development of the special properties of the zinc sulfide phosphor advantageous according to the invention to dispense with a Nachdotieren the present after the high temperature annealing annealing charge with additional copper. Thus, the desired luminescence properties of the phosphor according to the invention can be achieved with a drastically reduced process costs, namely without the required in the prior art step of Nachdotierung.
Working up of the annealing material can then simply by gentle, deagglomerierende wet milling and carrying out several washing processes. Consequently effected in these embodiments, no treatment with a dilute mineral acid, no Nachdotieren the intermediate with Cu and no re-treatment with a dilute acid, and no re-annealing. This intermediate product is cooled down before the further steps and washed with H 2 O.
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Furthermore, a deagglomeration of the intermediate product with the use of ceramic balls and with the addition of a grinding aid, such as choline, pyrophosphate or potash water glass takes place. Finally, a treatment is carried out with dilute mineral acid, whereby in particular the surfaces of the powder grains of the intermediate product to be modified. The mineral acid is preferably formed by hydrochloric acid.
In these embodiments, a Nachdotieren of the intermediate product is carried out with Cu, whereby the produced phosphor is formed. The Nachdotieren takes place in that Cu in the form of a Cu-containing chemical compound, such as CuSO 4 is added to the intermediate. Das Tempern dauert bevorzugt mindestens eine Stunde. Annealing preferably takes at least an hour. The nachdotierte phosphor can be regarded as an intermediate product of a further modified embodiment again and is treated, in this case with a dilute mineral acid, after it has been tempered.
The dilute acid is preferably formed by dilute nitric acid. After treating with dilute acid, this intermediate is washed again, dried and annealed. The synthesis according to the invention the zinc sulfide EL phosphor having in addition to its efficient electroluminescence a photoluminescence and a certain detectable color change of the UV-stimulable luminescence, requires the above-mentioned specific conditions.
This can be explained by the current state of knowledge, among other things, that the manifestation and effectiveness of at least two different activatable radiation centers will be affected in the ZnS matrix not only on the particular inventive phosphor composition but to a large extent on preparative factors. The setting of the preparative conditions relevant for the inventive production of the zinc sulfide phosphor. Starting from the preparation disclosed herein steps optimized synthesis conditions may possibly be experimentally found easily despite the complexity of the characteristic fluorescent properties of Elektroluminophors and despite the different influences of preparative factors.
If necessary, only a few tests to be carried out under laboratory conditions to be required. On the other hand, is expressly noted in this context that the synthesis according to the invention of the phosphor known process steps can be supplemented by further on.
Nach Literaturangaben kristallisiert ZnS unterhalb von 1. The phosphor produced in the manner described generally has good deagglomerated particles having average particle sizes of between about 2 microns and about 20 microns. The particle size distribution can be controlled by the preparation conditions and set. The average grain sizes of Elektroluminophors invention are not limited to the exemplified range.
The phosphor according to the invention is preferably characterized by the inventive method for its manufacture. The security feature according to the invention comprises one or more embodiments of the zinc sulfide phosphor of the invention. It includes a security feature, comprising one or more embodiments of the zinc sulfide phosphor of the invention. Das Sicherheitsmerkmal kann auf unterschiedliche Weise auf oder in das Sicherheitsdokument auf- bzw. The intensity of these bands compared to the series lines is much greater when the arc is operated in hydrogen.
Under these conditions the bands are especially strong in the optically excited radiation making it possible to observe groups 2, 3 and 4. The individual members in each group were not resolved in the optically dxcited radiation.
These bands constitute all or part of what Sommerfeld has called a "band system. The intensity of these band groups relative to the series lines in the optically excited radiation is much greater than in the arc radiation. Further experiments with improved apparatus are in progress. Bands similar to group 1 have been observed in the spectrum of cadmium4'7 but Terenin8 did not mention having observed them in the optically excited radiation of cadmium vapor.
The reproduction of his arc spectrum did not show these bands to be present, probably because his arc was not as effectively cooled as that used in this work and was not operated in hydrogen. Impact Fluorescence. When this tube was illuminated by the watercooled quartz mercury arc the mercury lines which were observed by Wood,1 the X 1S-2p2 zinc line, and a strong line at X i 6 were obtained in the optically excited radiation.
The appearance of the zinc line is explained by what has been called "sensitized fluorescence," but which is perhaps better described as "impact fluorescence. The excited mercury atom possesses more energy than is required to excite a normal zinc atom. The extra energy is changed into increased kinetic energy of the two colliding atoms.
Impact fluorescence has been observed and interpreted for several metals by Cario and Franck, 8 Kopferman9 and Donat. Further observations of this effect will be made using higher temperatures and greater mercury vapor pressures. In conclusion I wish to express my thanks to Dr. Mendenhall who suggested the problem and directed the work. Read more. Photosensitized Decompositions by Excited Mercury Atoms. Production of hydroxyl by water vapor discharge. Cruel Zinc Melodies. Vapor Trail. Zinc Handbook. Toxicological profiles - Zinc. Highly Excited Atoms. Optimizing the growth parameters leads to smooth layers, ending up in a mirror-like surface grown in 2D growth mode.
The latest results on p-type doping of such layers will be reported too. Ternary Zn,Cd O is a suitable candidate for opto-electronic devices operating in the visible spectral range. Band-gap related emission down to photon energies of 2. Growth on ZnO substrate improves significantly crystalline perfection rocking curve width: 45 arcsec. Application of specific post-growth annealing procedures increases the emission yield up to two orders of magnitude. In this way, the demonstration of laser action under optical pumping down to green wavelengths and up to room temperature on multiple quantum well structures has succeeded.
MgZnO homoepitaxial films grown by molecular beam epitaxy and requested characteristics of ZnO substrates to obtain high quality epitaxial films. Although the past decade has witnessed great advancements in the quality of ZnO materials, there still exist unresolved issues that threaten to hold up development of ZnO-based photonic and electronic devices. One such issue concerns the surface region, in which concentrations of donors, acceptors, traps, and recombination centers can be much different from those in the bulk.
In fact, in carrying out Hall-effect analysis, it becomes necessary to treat the surface as a separate sublayer, of effective thickness dsurf. Monday 21 January Show All Abstracts. ZnO hybrid microcavities grown by plasma assisted molecular beam epitaxy Paper Author s : Show Abstract. Characterization of an optically pumped ZnO-based 3 rd order distributed feedback laser Paper Author s : Show Abstract.
It lased in a single longitudinal mode over a large temperature range between 10K and K. The temperature-induced change of the ZnO refractive index agreed in an excellent way with literature values. ZnO is a very promising materials for new applications. Here we will present our results on the use of ZnO as a substrate for the growth of GaN.
Control of native point defects, chemical reactions, and surface morphology for ZnO electrical contacts Invited Paper Paper Author s : Show Abstract. We used depth-resolved cathodoluminescence spectroscopy, temperature-dependent current-voltage, deep level transient spectroscopy, and atomic force microscopy measurements to correlate the formation of native point defects and reaction layers as well as surface morphology at metal-ZnO interfaces and their effect on transport properties. These reactions and defect formation with annealing reveal a thermodynamic control of blocking versus Ohmic contacts.
These measurements reveal both increased doping and defects near these interfaces that promote tunneling and hopping transport. These results provide crystal quality, surface conditions, metallization, and thermal processing metrics for controlling ZnO electrical contacts. Light emitting diodes LEDs based on the combination of n-ZnO nano-wires and different p-type organic semiconductors are demonstrated.
Structural, electrical and optical characterization results are to be presented. The adopted approach is suitable for large production and hence represents a potential candidate for commercialization. Rational synthesis, doping, and optoelectronic application of zinc oxide nanowires Invited Paper Paper Author s : Show Abstract. A rich genre of ZnO nanostructures has been intensively studied for nanoscale optoelectronics, electronics, and biotechnology. I will report some recent progresses on the rational synthesis, complimentary doping, and device applications of ZnO nanowires NWs.
Specifically, I will discuss the p-type doping of high-quality ZnO nanowires using phosphorus pentoxide as the dopant source during the chemical vapor deposition. The synthesis of p-type ZnO NWs enables novel complementary ZnO NW devices and opens up enormous opportunities for nanoscale electronics, spintronics, optoelectronics, and medicines.
These results suggesting ZnO NWs offer significant opportunities as functional devices. Low-temperature wet chemical synthesis of ZnO nano-micro structures for use in gas sensing Paper Author s : Show Abstract. We have synthesized nano flower-like ZnO by a low-temperature wet growth. Zinc acetate dihydrate was dissolved in deionized water and mixed with ammonium hydroxide so as to create an alkaline environment. Glass substrates were immersed into the solution and hydrothermal treatment was carried out.
Upon hydrothermal treatment, the solution decomposed into ZnO and formed an adherent layer on the glass substrates. The response to ethanol gas exposure of the fabricated layers was discussed in reference to the surface chemical properties of the nano structures. Controlled growth of ZnO nanowires by nanoparticle-assisted laser ablation deposition Paper Author s : Show Abstract.