EP0914300A2

EP0914300A2 - Low-energy phonon spectrum glass composition, method for the production and use thereof

Info

Publication number: EP0914300A2
Application number: EP98929219A
Authority: EP
Inventors: Lothar Weber; Helmut Sautter; Jürgen Graf; Frank Gross; Peter LÖFFLER; Ingo Lang; Martin Mennig; Helmut Schmidt; Ulrich Sohling
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-04-15
Filing date: 1998-04-09
Publication date: 1999-05-12
Also published as: JP2000512611A; WO1998046538A2; WO1998046538A3

Abstract

The invention relates to the production of a glass composition based on rare earth metal doped chalcogenide and chalcohalide glass with or without co-doping and to a method for producing the same, in addition to a method for producing thin, transparent glass layers and the use thereof as optical components. The glass composition contains at least one element from the third main group, at least one element from the fourth main group, at least one halogenide element and at least one rare earth metal element as a doping additive, in addition to sulfur.

Description

Glass composition with a low energy phonon spectrum. Process for their preparation and their use

The invention relates to a transparent glass composition according to the preamble of claim 1, which has very good transmission properties far into the infrared range of the electromagnetic spectrum and has a phonon spectrum of low energy. A method for producing this glass composition is described, as well as a method for producing thin layers from the glass composition according to the invention and their use for producing optical components.

State of the art

In recent years, a variety of rare earth element doped glass compositions for use in fiber transmission systems, laser diode pumped fiber optic amplifiers (LD-PDFA), and fiber optic cables have been described.

It is known that there are two so-called

There are "telecommunications windows" in rare earth-doped glass fiber transmission systems in which optical amplification takes place at a fluorescence wavelength of the excited rare earth metal cations of 1.3 μm and 1.5 μm. Very good and commercially usable successes are currently being achieved achieved with Er-doped silicate fibers for use in the 1.5 μm telecommunications window (EP 0439867 Bl).

In contrast, there are corresponding glass compositions for potential applications in the second optical

Telecommunication windows at 1.3 μm are not available to a satisfactory degree. Almost all of the glasses described so far are based on a sulfide or oxide matrix. Disadvantages of almost all of these previously known glasses are their strong hydrophilicity, the poor band position of the emitted radiation or the poor solubility, i.e. the poor incorporation of rare earth metal cations into the structures of such glasses. US Pat. No. 5,389,584 describes AsGe sulfide glasses with gallium and indium additives which have good solubility for rare earth metals. This is supposed to be based on the fact that gallium sulfide is present in the glass structure in the form of side-bridged GaS4 tetrahedra, in the tetrahedron gaps of which rare earth metal cations can be embedded as well as in the comparable purely oxidic glasses, which typically have a three-dimensional network of relatively ionically bound MO4 tetrahedra, in which M is a so-called “network-forming” element, for example silicon, phosphorus, aluminum, boron, etc.

The only commercially available glass to date which has fluorescence and thus optical amplification in the 1.3 μm telecommunication window is the so-called “ZBLAN” glass based on fluoride, doped with praseodymium, for example described in the article by M. Yamada et al. In : IEEE Photonics Technology Letters, 1992, 4, 994-996.

The co-doping of glasses with a second element of the rare earth as "pump ion", which has a lower excitation wavelength for the fluorescent ion Enabling energy transfer from the pump ion to the emitting ion and, moreover, making efficient use of the generally much higher absorption cross section of the pump ion compared to the laser-active ion, poses an unsatisfactorily solved problem with regard to this

Fluorescence lifetime and quantum efficiency. In this case, the Pr-doped ZBLAN glasses, co-doped with Yb, provide only unsatisfactory results (P. Xie and T. R. Gosnell in: Electronics Letters 1995, 31,191). The same applies to the glass compositions (also hygroscopic) doped with Dy or Pr and containing Yb as a co-doping element (US Pat. No. 5,379,149).

These problems mentioned are due to the choice of the glass matrix, i.e. to the resulting split in terms of the

Attributed to rare earth metal cations. This is based on the close proximity of the low-lying energy levels to the high-lying ¹ G4 term of the upper laser level. The 1.3 μm transition from Pr ^{3 +} takes place between the high ¹ G4 energy level and the low ³ H ₅ energy level. In the energy level diagram of Pr ³⁺ , shown in Figure 1, the energy difference between ¹ G ₄ and ³ F _{4 is} approximately 3000 cm ^" . It is known that excited ¹ G ₄ states due to radiationless, spin-prohibited phonon transitions to the ³ F4 state are quenched, provided sufficient high-energy phonons are available. In general, the highest phonon energy, for example in oxide glasses, is of the order of 1100 cm ^" , so that only three such phonons are required to make up the difference between the ¹ G ₄ level and to bridge the ³ F ₄ level without radiation. In extreme cases, this means that no measurable emissions can be observed at 1.3 μm. ZBLAN glass matrices solve this fundamental problem by using fluorides, which change the term splitting of the rare earth metal cation and also the Reduce the maximum possible phonon energy to approx. 500 cm ^" . At least 6 phonons are therefore required to bridge the energy difference ¹ G ₄ - ³ F.

It was therefore the task to solve a glass composition which has a low-energy phonon spectrum, which can thus be used as a matrix for optically active rare earth metal cations, which in this matrix has a long fluorescence lifetime with high quantum efficiency with favorable band positions of the emitted radiation around 1. 3 μm. In addition, such a glass composition should be made available, which has an additional pump ion of the rare earths as co-doping for efficient excitation, for example for optical amplifiers. Furthermore, a method for producing thin layers from the glass composition according to the invention should be developed.

Advantages of the invention

The glass composition according to the invention with the characterizing features of the main claim offers the surprising advantage that the combination of sulfur and halogens in the form of their anions gives rare earth-doped chalchalide glasses which have a surprisingly favorable band position of praseodymium fluorescence, a long fluorescence life and good chemical resistance, especially against moisture. An important reason for the advantageous high solubility of the rare earth elements in the glass composition according to the invention lies in the use of halide anions, which moreover influence the position of the fluorescence band. Due to the addition of halides, the glass composition according to the invention shows a high level compared to analog sulfide glasses Fluorescence life of up to 460 μs. By setting the halide content to a minimum, the glass composition has good chemical resistance, in particular to atmospheric humidity. The glass composition according to the invention, for example in the case of Ge ₂ 2, 2 ^Sn 6, 4 ^In 3, 2 ^S 63, 3 ^C1 4, 8 doped with 1040 mol ppm praseodymium, has a fluorescence lifetime of 460 μs. In addition, the glass composition according to the invention has a particularly low phonon energy, which largely prevents the quenching of the laser energy from ¹ G4 to ³ F by radiation-free phonon transitions. For example, Gβ24 ιln ₇ S48 2 20 6 _< doped with 1000 mol-ppm praseodymium has a maximum phonon energy of 436 cm ^" measured by Raman spectroscopy. Comparable values, described for example in the

Articles by J. Heo and JD MacKenzie in: Journal of Non-Crystalline-Solids 1989, 211, 29, show for the best known system Ge3gSgoIιo doped with 1000 mol-ppm praseodymium, a maximum phonon energy of 476 cm ^" .

Advantageous refinements of the glass composition according to the invention result from the features mentioned in the subclaims.

The use of sulfides of the elements of the fourth or fifth main group, which have a three-dimensional tetragonal solid structure, ie. H. whose MS4 units form edge-linked tetrahedron chains. They are isostructural to corresponding oxidic glasses, in particular silicate glasses, and enable good solubilities for almost all rare earth metal cations.

The addition of lead, antimony or bismuth is preferred, which leads to particularly high chemical resistance and furthermore supports the further incorporation of rare earth cations.

In a particularly advantageous manner, up to 10 atom% of oxygen anions are incorporated into the invention

Glass composition built in, resulting in an even larger

Solubility of the rare earth cations, especially ytterbium, due to the structural effects mentioned above.

This enables the simplified production of Yb ³⁺ co-doped praseodymium-doped sulfide glasses, in which a

Energy transfer from the excited ² Fs 2 Yk> ³⁺ term to the laser active ¹ G4 Pr ³⁺ term.

In a further advantageous embodiment, the rare earth-doped chalchalide and

Sulfide glasses co-doped with Yb or Er, resulting in low excitation wavelengths for fluorescence emission and a higher fluorescence efficiency of the rare earth cation. This considerably simplifies the use of low-cost, low-power laser diodes.

In a preferred process, the glass composition is produced in such a way that pure elements, halides or sulfides of the corresponding metals and semimetals are used as constituents. This can result in a high Purity of the substances used can be achieved without any problems, since in particular pure elements can be supplied from the corresponding manufacturers in the highest possible purity level. Halides and / or sulfides may be purified by distillation or sublimation.

In a preferred embodiment of the method, the constituents of the glass composition are mixed intimately and reacted with one another in a melting process with the exclusion of air. This prevents oxygen anions from being incorporated into the glass composition in the case of non-oxide glasses. The quenching of the glass composition thus obtained is advantageously carried out either in air or in water.

In order to produce transparent thin layers, the raw glass thus produced is comminuted to powder particles in a particularly advantageous manner and taken up in a suitable solvent.

In a further preferred embodiment, a wet chemical method is used in which a colloidal solution of the powder particles taken up is used. This enables a high solids content of the solution to be achieved, which almost completely precludes later shrinking processes of the applied layers during thermal compaction.

In a particularly advantageous embodiment, the solvent used, preferably an aliphatic amine, such as propylamine, n-butylamine or ethylenediamine, acts as a stabilizer for the colloidally dispersed solution of the powder particles. This addresses the known problems in the production of basic sulfidic rare earth-doped glass solutions, which are among these Conditions have a precipitation of the inevitably arising rare earth hydroxides, avoided particularly advantageous.

drawing

The invention is explained in more detail below in exemplary embodiments with reference to the associated drawings. Show it

FIG. 1 shows an energy level diagram of Pr ⁺ ,

FIG. 2 shows an energy level diagram of Yb ³ + and Pr ³⁺ and the energy transfer from Yb ³⁺ to Pr ³⁺ ,

FIG. 3 shows a fluorescence spectrum of the 1.3 μm emission band of the ¹ G4 ~ ³ H5 transition in a glass composition according to the invention,

Figure 4 shows the fluorescence lifetime of the ¹ G4 ~ state of

Pr ³⁺ as a function of the chloride content of a glass composition according to the invention,

FIG. 5 shows the fluorescence lifetime of the ¹ G4 state of Pr ³⁺ as a function of the Pr ³⁺ doping level of a glass composition according to the invention.

FIG. 6 shows the excitation spectrum of a co-doped glass composition according to the invention,

Figure 7 is a three-phase diagram of an inventive

Glass composition with an area 1 and an area 2 Embodiments

Examples of the glass composition according to the invention are shown in Tables 1 to 5. The tables show the doping levels of Pr, Er or Yb in mol ppm, based on the total concentration of cations.

Figure 1 shows the energy level scheme of Pr ³⁺ . The abscissa represents the relative energy in the unit 10 ³ cm ^-1 . Pr ³⁺ is raised from the ground state ³ H ₄ by an excitation energy of approx. 1020 nm, for example by a laser, to the laser energy level ¹ G4. By falling back to ³ H ₅ , fluorescence radiation with a wavelength of approximately 1.3 μm is emitted, in this case of 1.33 μm (1330 nm).

FIG. 2 shows the energy level diagram for the energy transfer of a praseodymium chalchalide glass composition according to the invention co-doped with Yb ³⁺ . The abscissa represents the relative energy in the unit 10 ³ cm ^~ ¹ . In this case, Yb is first ³⁺ _{7 2} transferred from the ground state ² F by a power supply, for example by a laser diode of 980 nanometers in the F _{_5/2} state, the spin-forbidden its energy nonradiative on the emitting ¹ G ₄ state of Pr ³⁺ transmits. The desired wavelength is emitted by falling back of the now excited Pr ³⁺ from ^ 4 to ³ H5. In all examples of the glass composition according to the invention, the emission maximum is between 1325 and 1345 nm.

Figure 3 shows the fluorescence wavelength of the glass composition Ge28 ^τ -n6 ^s 56 ^c -'- 10 ( ^s - Table 1), doped with 1000 mol-ppm praseodymium with excitation with 1025 nm, the 1.3 μm fluorescence of the Pr ³⁺ Transition is at 1338 nm. The abscissa shows the fluorescence intensity in relative units and the ordinate the wavelength in nm.

Table 1: Glass composition based on sulfide and sulfide chloride.

FIG. 4 with the associated table 4 shows the fluorescence lifetime in μs of the ¹ G state of Pr ³⁺ as a function of the chloride content in the glass composition Ge22 ^Sn 6 4 ^In 3 2 ^s 67-x ^c - ^L x is clearly recognizable that an optimum between 6 and 13 atomic% chloride content is achieved based on the total anions. The maxima are between 6.5 and 10 atom% chloride content based on the total anions. From a chloride content of 25 atomic% based on the total anions of the glass composition, the glass decomposes and in particular hydrolyses.

Figure 5 with the associated Table 5 shows the fluorescence lifetime in microseconds of the ¹ G4 state of Pr ³⁺ on the abscissa as a function of the Pr doping level on the ordinate in the glass composition Ge ₂ gIng_ _x Pr _x S5 I ₁ o. It can be seen here that low doping with praseodymium leads to longer fluorescence lifetimes. The maximum lifetime is achieved with the composition Ge28 ^τ - ⁿ 6 ^s 56 ^I 10 doped with 1000 mol ppm Pr ³⁺ .

Figure 6 shows the excitation spectrum of the glass composition Ge ₂ 5 7 t> ι 9 (In + Yb) _5/7 Sg ₀ 4Clg g (s. Table 2), which ppm molar of 5000 mol ppm of Pr ³⁺ and 10000 Yb ^{3 + is} doped or co-doped. The abscissa indicates the fluorescence intensity in relative units and the ordinate that

Excitation wavelength in nm. FIG. 6 shows the difference in the fluorescence intensity of the 1.3 μm fluorescence of Pr ³⁺ when excited with different wavelengths. Excitation of the Yb ³⁺ ions with 987.7 nm shows that the transferred energy becomes a

1.3 μm fluorescence from Pr ³⁺ leads, which has more than twice the fluorescence intensity compared to a direct Pr excitation at 1025 nm. It is thus found a highly effective energy transfer of ² F _{_5/2} (Yb ³⁺⁾ after ¹ G ₄ (Pr ^3+). Table 2: Glass composition with Sb and Pb addition.

In all examples of the glass composition according to the invention, which can be seen, for example, from the tables, it can be seen that the use of germanium sulfide in conjunction with halides increases the solubility of rare earth cations. For example, compositions have the shape

Ge ₂ 5 7P _] _ gdn + Yb ^ 7S _] _ gC] _ ₄ 8 ( ^s - Table 2) Solubilities of 10000 mol-ppm Yb ³⁺ and 5000 mol-ppm Pr ³⁺ . Table 5 shows even higher solubilities in the order of up to 20,000 mol ppm.

FIG. 7 shows a three-phase diagram for a glass composition according to the invention which contains Ga2S3, Sb2S3 and GeS2 as essential constituents. Area 1 includes the prior art disclosed in U.S. Patent 5,392,376 for such mixtures. The invention Glass composition comprises area 2, which is identified by points A, B, C and D.

All the exemplary embodiments of the glass composition according to the invention have in common a long fluorescence lifetime τ _{eff of} up to 460 μs. Likewise, the phonon energy of the glass composition according to the invention is generally very low. For example, in Ge24, _l ^In 7, l ^s 48 2 ^I 20 6 (see Table 1), doped with 1000 mol ppm Pr ³⁺ , τ _eff 309 μs and the phonon energy is 436 cm.

Table 3: Glass composition with 2 different halides.

The glass composition Ge25 2 ^p b 9 (In + Yb) 5 gS58 5 I8 9 (see Table 2), doped with 10000 mol-ppm Yb and 5000 mol-ppm Pr, has a lifetime τ _eff of 294 μs when excited with 980 nm , ie excitation of the Yb ³⁺ , and a lifetime τ _eff of 376 μs with direct excitation with 1020 nm of Pr ³⁺ .

The glass composition according to the invention, characterized by a few exemplary embodiments, also has good temperature stability, indicated by the glass transition temperature T _g . In addition, the glass composition according to the invention has a very high moisture resistance.

The glass composition according to the invention is produced, for example, by melting the constituents in cleaned, evacuated silica glass ampoules and then quenching them in air or in ice water. Starting materials are used in the highest commercially available degrees of purity. If necessary, the starting materials by sublimation or

Distillation further cleaned. The starting materials, in particular high-purity germanium, indium, tin, erbium, Pr2S3, Yb2S3, Er2S3 and PbCl2, were obtained from Chempur, GeBr4, Sb and iodine from Alfa, Johnson Matthey, purified sulfur from Vitron, InCl3 from Strem and SrS from Cerac.

Thin glass film layers are produced from the glass composition according to the invention by means of the new method according to the invention.

So far, thin films of glass layers have generally been produced using sol-gel processes, for example described in the book by: RW Kahn, P. Hasen, EJ Kramer (eds.J, Material Science and Technology, Glasses and Amorphous Materials, p. 112, VCH Weinheim, 1991.

In the new wet chemical process according to the invention, substrates can be coated with colloidal solutions with a high solids content. After the melting process and quenching, the raw glass is pulverized and colloidally dissolved in a solvent, preferably an aliphatic amine, for example propylamine, n-butylamine or ethylenediamine. In order to avoid a quick dissolution of the glasses in their ionic components, the Solvents also act as stabilizers for the colloids, which is ensured by the aliphatic amines used. The colloidal solutions in aliphatic amines can be diluted with suitable inert solvents, for example acetone, ethanol, propanols or acetonitrile. Furthermore, it is also possible to prepare colloidal solutions using solvents which are a mixture of alphatic amines and the inert solvents. The colloidal solutions obtained in this way are used to produce praseodymium-doped chalcogenide and chalcohalide glass layers by means of a known immersion or spin-on process on a substrate, for example ITO (indium tin oxide), plastics or other suitable substrates, and then by thermal Aftertreatment compacted.

These layers are then laterally structured in a simple manner by processes known per se, for example ion etching or UV exposure.

The production of a thin layer is described using a Pr-doped As2S3 glass. Of course, this does not represent a limitation of the invention, but rather thin layers can also be produced from the glass composition according to the invention with this method. 0.1 g of a Pr-doped with 300 mass ppm

AS2S3 glasses are dissolved in 1 ml propylamine and stirred at 20 ° C for 1 h. After filtration through a filter with an average pore size of 0.5 μm, a clear yellow solution is obtained. This can be used to produce coatings on glass substrates by dip coating, spin coating or spray coating. The thermal compression takes place at 130 ° C. For example, the coating solution can be spin-coated at 1000 rpm for 30 seconds and then compacted at 130 ° C. Produce layers with a thickness of 0.5 μm on which the 1.3 μm fluorescence can be detected.

Likewise, it is of course possible to produce fibers and cables from the raw glasses in processes known per se. The glass composition according to the invention is thus used in the form of fiber lasers, fiber amplifiers, glass lasers, planar waveguide lasers, planar waveguide amplifiers, etc.

Table 4: Variation of the chloride content in atomic% of the anions.

Table 5: Variation of the Pr ³⁺ doping level with a Ge-In-SI glass composition.

Table 6: Ge-Sn-Ga-S-Hal glass composition with high Pr doping (Hai = Ii, Br)

Table 7: Pr ³⁴ -doped Ge-Ga-Sb-S glass composition

Claims

Expectations

1.Transparent glass composition with a transmission in the near to far infrared range of the electromagnetic spectrum and a phonon spectrum of low energy, the at least one element of the third main group, at least one element of the fourth main group, at least one element of the halides and at least one element of the rare earth metals as a doping additive and Sulfur, characterized in that the glass composition 7-35 atom% Ge, 0.01-30 atom% Sn, 0.001-30 atom% of at least one element selected from Pb, Sb, Bi, 0.01-20 atom% In, Contains 0.001-3 atom% of the elements of the rare earth metals, 40-70 atom% S and 0.01-20 atom% of an element of the halides.

2. Glass composition according to claim 1, characterized in that the glass composition additionally contains at least one further element of the fourth and / or fifth main group, the sulfide of which has a three-dimensional solid structure, in particular a tetragonal solid structure.

3. Glass composition according to claim 2, characterized in that 0.001-20 atom% Ga are contained.

4. Glass composition according to claim 1, characterized in that the glass composition contains at least one element of the alkali and / or alkaline earth metals.

5. Glass composition according to claim 4, characterized in that the element or elements of the alkali and / or alkaline earth metals are each contained with up to 10 atom%.

6. Glass composition according to claim 1, characterized in that up to 10 atom% of oxygen are contained.

7. Glass composition according to claim 1, characterized in that at least one element of the rare earth elements Pr, Yb, Er, Dy, Nd is contained in the form of its trivalent cation as a doping additive.

8. Glass composition according to claim 7, characterized in that Pr or Dy or Nd and at least one further rare earth element selected from Yb and Er is contained as a co-doping additive.

9. Glass composition according to one of the preceding

Claims, characterized in that the

Glass composition a medium

Glass transition temperature (Tg) between 200 ° C and 700 ° C.

10. A method for producing a transparent glass composition with a transmission in the near to far infrared range of the electromagnetic spectrum and a phonon spectrum of low energy with components according to one of claims 1 to 6, characterized in that the components as pure elements and / or halides and / or Sulfides are used.

11. Process for producing a transparent glass composition with a transmission in the near to Far infrared range of the electromagnetic spectrum and a phonon spectrum of low energy with components according to claim 6, characterized in that the components are used as pure elements and / or halides and / or oxides and / or sulfides.

12. The method according to claim 10 or 11, characterized in that the elements of the rare earth metals are used as sulfides and / or halides and / or pure elements.

13. The method according to any one of claims 10 to 12, characterized in that the constituents of the glass composition are mixed intimately and react with one another in a melting process with the exclusion of air.

14. A method for producing transparent glass layers with a transmission in the near to far infrared region of the electromagnetic spectrum and a phonon spectrum of low energy according to one of claims 1 to 9, characterized in that after the production of a raw glass, the glass composition is crushed into powder particles and in a suitable Solvent is added.

15. The method according to claim 14, characterized in that the solution of the powder particles is colloidal.

16. The method according to claim 14 or 15, characterized in that the solvent simultaneously as

Stabilizer for the colloidally disperse powder particles acts.

17. The method according to claim 14, 15 or 16, characterized in that aliphatic amines are used as solvents.

18. The method according to claim 14, characterized in that a substrate is coated with a colloidal solution of the powder particles.

19. The method according to claim 18, characterized in that the coating of the substrate is carried out by immersion and / or spin-on and / or knife and / or spray process.

20. The method according to claim 18 or 19, characterized in that the coated substrate is thermally post-treated.

21. The method according to any one of claims 18 to 21, characterized in that the layer thickness is at least 1 micron.

22. The method according to any one of claims 18 to 21, characterized in that the layer applied to the substrate is laterally structured.

23. Use of a glass composition with a transmission in the near to far infrared range of the electromagnetic spectrum and a phonon spectrum of low energy according to one of claims 1 to 10 for the production of optical components, in particular light sources and optical amplifiers.