DE19610433C2 - Luminescent glass and method of making and using this glass - Google Patents

Description

The invention relates to luminescent glasses, in particular for users applications in optics, integrated optics, optoelectronics and Laser technology can be used, according to the preamble of claim 1.

The invention further relates to a method for producing these glasses according to the preamble of claim 6.

The invention further relates to applications of these glasses according to the Preamble of claim 11.

The possibility of generating laser radiation by means of rare earth ion (SE) -doped glasses has been known since 1961 (E. Snitzer; Optical Maser Action of Nd ³⁺ in a Barium Crown Glass, Phys. Rev. Lett. 7, 444-446 ( 1961)). It is also known that the rare earth ions in glasses - in contrast to SE-doped crystals - have an inhomogeneous space distribution (J. Wong, CA Angell, Glass - structure by spectroscopy, Marcel Dekker (1976)). Naturally, therefore, the SE absorption or emission transitions show an inhomogeneous broadening (MJ Weber (ed), CRC Handbook of Laser Science and Technology, Vol. IV, Optical Materials, CRC Press Boca Raton, FL (1986)). This in turn leads to smaller stimulated emission cross sections and higher laser thresholds in glasses. This disadvantage can also be used in special circumstances: a broad inhomogeneous laser line is used to generate ultra-short laser pulses with high pulse power (W. Koechner; Solid State Laser Engineering, Springer New York (1992).

Glasses have less heat conduction than crystals, so that glass lasers can usually only be used in pulse mode. Otherwise there is a risk of thermal-mechanical breakage. Depending on the excitation intensity, on the pump geometry and, among other things, on the respective cooling conditions, pulse train frequencies are typically not greater than about 10 Hz. It must be ensured that the portion of the excitation energy that cannot be used as laser energy (heat loss due to radiation-free deactivation) can be released to the surrounding medium. For example, special Er ³⁺ glass lasers can also be operated continuously (cw) if the radiationless deactivation processes are minimized (D. Ehrt, W. Seeber, E. Heumann, M. Ledig; Sensitized erbium glasses with high efficiency for laser technology, patent DD C03C / 260 18 A1 (16. 11. 1988)) and the heat dissipation is optimized. Also z. B. the small quantum defect of the Yb ³⁺ laser (absorption band around 970 nm, emission band around 1040 nm) is well known and has recently been used to realize efficient Yb lasers based on fluoroapatite crystals. (e.g. BLD DeLoach, SA Payne, LK Smith, WL Kway and WF Krupke; J. Opt. Soc. Am. B. 11 (1994) 269 and SA Payne, LK Smith, LD DeLoach, WL Kway, JB Tassan o and WF Krupke; IEEE J Quantum Eectron. QE-30 (1994) 170). The production of these crystals in high optical quality and in volumes <1 cm ³ causes problems. Experiments published so far call crystal dimensions <1 cm (e.g. BSA Payne, L. K Smith, LD DeLoach, WL Kway, JB Tassano and W. F Krupke; IEEE J. Quantum Eectron. QE-30 (1994) 170). In addition, the processing of crystals is usually more difficult than that of glasses. Laser activity at room temperature has been shown, for example, in Yb-doped phosphate glasses (U. Griebner, R. Koch, H Schönnagel, S. Jiang, MJ Myers, D. Rhonehouse, SJ Hamlin, WA Clarkson, DC Hanna; Laser performance of new ytterbium doped phosphate laser glass, ASSL 1996). In these materials, the highest differential efficiency so far was 43% at a threshold of approx. 190 mW. However, phosphate glasses naturally show an increased tendency to incorporate OH assemblies, which are known to have luminescence-quenching properties. Due to an advantageous fiber geometry, 77% differential efficiency could be achieved using Yb-doped silicate glass fibers (DC Hanna, RM Percival, IR Perry, GS Smart, PJ Suni and AC Tropper; J. Mod. Opt. 37 (1990)), the coupling however, excitation light into the fiber is complicated and the achievable laser output is limited. In fluoride-phosphate glasses, excitation by means of Ti-sapphire laser and 3% decoupling achieved approx. 41% differential efficiency at threshold energies around 145 mW (E. Mix, E. Heumann, G. Huber, D. Ehrt, W. Seeber; Adv Solid State Lasers, Memphis, TN, Tech. Dig., WB 5-1 (1995) 230).

By reducing the phosphate content in these glasses, the Efficiency in a glass with 2 mol% phosphate increased to approx. 55% become. However, the reduced phosphate content worsened the Glass formation tendency and the optical quality. There was also an increase the threshold energy observed at about 230 mW.

The influence of the concrete local structure of built-in rare earth ions, the is called their first and second coordination sphere, based on the position of Energy levels, transition probabilities as well as ultimately on Laser properties was and is the subject of intensive research (e.g. S.E. Stokowski, R.A. Saroyan and M.J. Weber; Nd-doped laser glasses / Spectroscopic and physical properties, LLL University of California, Livermore (1981) and L.D. De Loach, S.A. Payne, L.L. Chase, L.K. Smith, W.L. Kway and W.F. Krupke; IEEE J. Quantum Electron. QE-29 (1993)  1179). The electronic position of the terminal Yb laser level in Fluorapatite crystals in connection with electron-phonon changes effects processes with the inclusion of suitable phonons. about a variation of the local structure of fluoride-phosphate glasses with the aim an effective coupling of phonons to the electronic transitions, especially of the ytterbium ion, however, there is no evidence.

It is Z. B. according to DE-OS 36 34 676 known to manufacture special glasses based on fluoride-phosphate. These glasses are characterized by refractive indices n _e = 1.47 - 1.50 and Abbe numbers v _e = 85 - 80 and were developed with the aim of an extreme optical position in the n _e -v _e diagram. There was no targeted variation of the local structure to improve the luminescence or laser properties of these glasses.

Laser materials were found in Silikattechnik 41 (1990), No. 7, pp. 230-233 the base of fluoride-phosphate glasses presented by a general model regarding the main structural supports ((fluorometallate Chains) in fluoride-phosphate glasses. In those examined there However, glasses do not form a special one either Local structure of the SE ions, combined with an adapted, advantageous Electron-phonon interaction.

It is also known (e.g. DD 262 017 A1, DD 262 018 A1) to incorporate so-called sensitizer ions (e.g. Cr ³⁺ , Mn ²⁺ ) in fluoride-phosphate glasses with a defined composition in order to Energy transfer processes from sensitization to laser ion to increase laser efficiency. On the other hand, this improved utilization of the pump light from laser arrangements also poses problems, since opposing deactivation processes can lead to quenching of the luminescence.

DE 38 01 844 A1 presents a method by means of which a fluorophosphate glass with a total oxide content of 5 to 30% (cationic percentage) is to be produced. The term fluorophosphate glass is generally understood to mean a material whose structure is influenced by fluorophosphates, e.g. B. PO ₃ F ^- , is embossed, ie there are PF bonds in this glass. These bonds are unsuitable for the realization of an SE local structure with an advantageous electron-phonon interaction and must be avoided. The installation of YF ₃ is also disadvantageous for this.

Furthermore, optical glasses with extremely high anomalous partial dispersion are known (e.g. DE 30 44 240 C2) which do not contain any laser ions (e.g. Yb ³⁺ or Nd ³⁺ ). This means that these glasses cannot show any SE ion luminescence or laser activity and are therefore unsuitable as a luminescent material.

The object of the invention is to develop luminescent High efficiency ytterbium glasses for optics, integrated optics, Optoelectronics and laser technology, also called compact active materials at room temperature, both in impulse and in continuous (cw) Operation can be used and the wide tuning range ensure the laser wavelength. They are supposed to be economical and in be of good quality. Your application is intended for a wide variety Bring advantages to areas of science and technology.

In particular, glasses are to be developed for laser technology, which the Advantage of a built-in electron-phonon interaction Combine rare earth ions with the advantages of an optimized glass system.

According to the invention the task with a luminescent glass Features of claim 1 solved. The sub-claims 2 to 5 are advantageous embodiments of main claim 1.  

The invention of the novel luminescent glass is based on the fact that special local structures around built-in rare earth ions - hereinafter referred to as SE - in particular of ytterbium (Yb ³⁺ ) have been created, these special structures being formed by largely isolated, cluster-shaped groups tetrahedral anions around the SE ions are generated.

Host glasses are used which, in addition to cations and fluoride anions, in particular have tetrahedral anions, which are grouped around built-in rare earth ions, in particular ytterbium (Yb ³⁺ ), which results in clusters which are largely isolated from the rest of the glass network.

These host glasses are primarily melted from alkaline earth phosphates and fluorides, aluminum fluoride, compounds of rare earths as well as compounds with tetrahedral anions, whereby in the mixture of the glass melt: as cations
Mg ²⁺ 0-60 mol%
Ca ²⁺ 3-57 mol%
Sr ²⁺ 0-39 mol%
Ba ²⁺ 0-15 mol%
Al ³⁺ 2-39 mol% and
0.001-20 mol% in total
Lanthanium, cerium, praseodymium, samarium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and / or ytterbium ions,
continue as anions
1-35 mol% in total tetrahedral anions as phosphates, sulfates, vanadates, niobates and / or
Antimonates with:
less than or equal to 15 mol% in total sulfates, vanadates, niobates and / or antimonates and
65-99 mol% in total fluoride are present.

It has been found that the incorporation of tetrahedral anions in fluoridic glass melts enables the production of special local rare earth ion structures under certain manufacturing conditions. This results above all from the cluster-like arrangement of tetrahedral anions around rare earth ions (compare schematic representation in FIG. 1). The resulting groups are largely separated from groups of the same type.

Electron-phonon couplings of the vibrations of the tetrahedral anions with electronic transitions in the rare earth ion were detected. In Fig. 2, the existence of these couplings is demonstrated using the example of an electronic transition in the rare earth ion Gd ³⁺ , built into fluoride-phosphate glasses with different content of tetrahedral anions (here: phosphates). These couplings improve the luminescence or laser properties of the material. Appropriate synthesis compositions, in particular the choice of a suitable ratio of tetrahedral anions to the sum of the fluorides and the fluorides among one another, enable the formation of such clusters, with a glass-stabilizing effect occurring at the same time by reducing the tendency to crystallize of the fluorides. With a total content of 1-25 mol% of tetrahedral anions, good amorphous solidification is achieved. This is due to the concentration of the fluorides with respect to one another, the appropriate use of alkaline earth metal, rare earth ion and / or aluminum phosphate and the use of alkaline earth metal sulfate and / or vanadate and / or niobate and / or antimonate. Mainly MgF ₂ , CaF ₂ , SrF ₂ , BaF ₂ and AlF _{3 are used} as fluorides and strontium, sulfate, vanadate, niobate, antimonate and / or metaphosphate as compounds with tetrahedral anions. According to the invention, however, the cations of phosphates, sulfates, vanadates, niobates, antimonates and fluorides can be exchanged while maintaining the mol%, and oxides of vanadium, niobium and / or antimony can also be used.

According to the invention the object is further achieved in that 6 luminescent glasses are produced according to the steps of claim. The steps are that

• 1. Mixtures of components of the respective synthesis composition are preferably melted in the crucible (for example made of platinum or carbon) at temperatures in the range from 400 K to 700 K above the corresponding transformation temperature T _g . The temporary use of reactive gases in accordance with internationally known RAP technology (reactive atmospheric processing) can be advantageous.
• 2. Purification and homogenization of the glass melt at temperatures 50 K to 150 K above the maximum used in step 1)  Temperature.
• 3. Cooling the melt to temperatures 200 K to 300 K above of the respective transformation point.
• 4. Cast the glass into molds preheated to approximately transformation temperature T _g , which preferably consist of graphite.
• 5. Cool the molds filled with glass to room temperature.
• 6. Depending on the type of glass, a new on may also be required melting of the glass (remelting).
• 7. If necessary, the glasses can be cooled down by heating them up Temperatures about 20 K above the respective transformation point, Hold this temperature for about 30 minutes and controlled Cool down with cooling rates <15 K / h.

The invention further relates to applications of the luminescent glasses according to claim 11

• a) active tunable laser materials in compact form (bulk Geometry) for the generation of laser radiation in the wavelength range from about 1020 nm to 1085 nm at room temperature,
• b) active tunable laser materials in fiber form for generation from laser radiation in the wavelength range from approximately 1020 nm to 1085 nm at room temperature,
• c) amplification media for laser radiation in the wavelength range of about 1020 nm to 1085 nm, especially for building amplifiers chains for giant impulses,
• d) Media for generating ultra-short pulses, especially for users communications technology, measurement technology and spectroscopy and Farther
• e) Media for optical cooling of solids.

The invention is intended to be explained in more detail below on the basis of exemplary embodiments are explained.

Show it:

Fig. 1: Schematic structural model for forming a cluster-like grouping from a rare earth ion (here Yb ³⁺ ) and 3 tetrahedral anions each in a fluoridic glass matrix.

Fig. 2: Detection of electron-phonon couplings in fluoride-phosphate glasses by recording Gd ³⁺ -phonon sideband spectra at room temperature.

Fig. 3: threshold energy and slope efficiency of various inventive glasses.

FIG. 4 shows compositions of the mixture according to the invention glasses in mole percent and optical characteristics.

Fig. 1 shows a schematic structural model to form a cluster-like array of a rare-earth ion 1, in the example Yb ^3+, and three tetrahedral anions 2, embedded in a fluoridic glass matrix. Depending on the ion radius of the respective rare earth ion 1 , the tetrahedra are displaced along the specified spatial directions a, b, c for steric reasons.

This local structure of the rare earth ion 1 forms the basis for effective coupling of vibrations of the tetrahedral anion 2 with electronic transitions on the rare earth ion 1 , which are used for light generation based on the laser effect and for optical cooling based on the anti-Stokes luminescence are usable.

Fig. 2 illustrates the detection of electron-phonon couplings in phosphate fluoride glasses by incorporation of Gd ³⁺ -Phonon sideband spectra at room temperature. There are emission spectra at an excitation wavelength λ _exc = 273 nm shown. In addition to purely electronic transitions, here in the example ⁶ P _7/2 → ⁸ S _7/2 and ⁶ P _5/2 → ⁸ S _7/2 , phonon sidebands occur at around 323 nm, in the example ⁶ P _7/2 → ⁸ S _7/2 + ν ₃ (PO ₄ ^3- ). They are due to vibrations of the PO ₄ tetrahedron, which are known from IR / Raman spectroscopy (G. Blasse; Vibrational Structure in the Luminescence Spectra oflons in Solids, in Topics in Current Chemistiy, 171, Springer Verlag Berlin (1994) ).

These phonon sidebands are based on the steric arrangement of the tetrahedral anions 2 around the rare earth ion 1 and on the efficient coupling of the tetrahedral anions 2 to the electronic transitions of the rare earth ion 1 . They are decisive for the luminescent properties of these glasses.

In FIG. 2, emission spectra of the glass Nr. 6 (from Table in FIG. 4) with 20% phosphate, the glass no. 5 with 3% phosphate, as tetraeterförmiges anion, and a fluoride Comparison glass without phosphate content. The glass without a phosphate component shows no phonon sideband in the range around 323 nm. The glasses with a phosphate component show an increase in the phonon sideband with an increasing phosphate component. In the example according to FIG. 2, the energetic distance between the electronic transition ⁶ P _7/2 → ⁸ S _7/2 and the phonon sideband, depending on the phosphate content, is approx. 1050 cm ^-1 for glass No. 5 and approx. 1200 cm ^-1 for glass No. 6.

The glasses according to the invention have improved laser properties compared to the known glasses. In experiments using diode excitation of Yb-doped glasses, threshold energies of up to less than 80 mW and differential efficiencies of up to 69% were achieved (see also FIG. 3).

The scope of the invention is demonstrated by the examples listed in table 4 in FIG . However, the invention is not restricted to the examples given. Some compositions of the mixture of glasses according to the invention are given in mole percent and characteristic optical properties.

Reference list

1

Rare earth ion

2nd

tetrahedral anion
a, b, c spatial directions according to D ₃

-Symmetry

Claims (11)

1. Luminescent rare earth ion-doped glasses of high efficiency for optics, integrated optics, optoelectronics and laser technology, characterized in that the local structure of the rare earth ions ( 1 ) embedded in these glasses is shaped by cluster-shaped coordination with tetrahedral anions ( 2 ) . 2. Luminescent glasses according to claim 1, characterized in that ytterbium is incorporated as a rare earth ion in host glasses of the fluoride-phosphate type, these glasses too

• 1. 99.0 to 65.0 mol% of fluorides, predominantly MgF ₂ , CaF ₂ , SrF ₂ , BaF ₂ and AlF ₃ , and from
• 2. 1.0 to 35.0 mol% of phosphates are melted and
• 3. the concentration of all incorporated rare earth ions La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and / or Yb is less than or equal to 20 mol%.

3. Luminescent glasses according to claim 2, characterized in that up to 15 mol% sulfates are used at the expense of the phosphate content. 4. Luminescent glasses according to claim 2, characterized in that in total up to 15 mol% of vanadates and / or niobates and / or Antimonates are used at the expense of the phosphate content. 5. Luminescent glasses according to claims 2, 3 and 4, characterized in that as cations
Mg ²⁺ 0-60 mol%
Ca ²⁺ 3-57 mol%
Sr ²⁺ 0-39 mol%
Ba ²⁺ 0-15 mol%
Al ³⁺ 2-39 mol% and
0.001-20 mol% in total
Lanthanium, cerium, praseodymium, samarium, neodymium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and / or ytterbium ions,
continue as anions
1-35 mol% in total tetrahedral anions as phosphates, sulfates, vanadates, niobates and / or antimonates with:
less than or equal to 15 mol% in total sulfates, vanadates, niobates and / or antimonates and
65-99 mol% in total fluoride are present. 6. Process for the production of luminescent rare earth ion-doped glasses, characterized by the following production steps:

• a) mixtures of components of the respective synthesis composition are melted at temperatures in the range from 400 K to 700 K above the corresponding transformation temperature Tg,
• b) refining and homogenization of the glass melt at temperatures 50 K to 150 K above the maximum temperature used in step a),
• c) cooling the melt to temperatures 200 K to 300 K above the respective transformation point,
• d) casting the glass into molds preheated to approximately transformation temperature T _g and
• e) cooling the filled molds to room temperature.

7. The method according to claim 6, characterized in that a temporally limited use of reactive gases according to RAP technology. 8. The method according to claim 6, characterized in that depending of the glass type, the glass is melted again (remelting). 9. The method according to claim 6, characterized in that a Feinküh the glasses by heating to temperatures about 20 K above the respective transformation point, hold this temperature for approx. 30 Minutes and controlled cooling with cooling rates <15 K / h. 10. The method according to claim 6, characterized in that the Melt the glass in a crucible made of graphite (carbon) or out Platinum is done. 11. Applications of the luminescent SE-doped glasses with a special local structure as

• a) active tunable laser materials in a compact form (bulk geometry) for generating laser radiation in the wavelength range from approximately 1020 nm to 1085 nm at room temperature,
• b) active tunable laser materials in fiber form for generating laser radiation in the wavelength range from approximately 1020 nm to 1085 nm at room temperature,
• c) amplification media for laser radiation in the wavelength range from approximately 1020 nm to 1085 nm, in particular for the construction of amplifier chains for giant pulses,
• d) media for generating ultra-short pulses, especially for applications in communication technology, measurement technology and spectroscopy, and further
• e) Media for optical cooling of solid-state lasers.