P. Sarkisov International Laboratory of
Glass-Based Functional Materials
 

 D. Mendeleyev University of Chemical Technology of Russia
 English   

New light-emitting glass-based systems

The fabrication of luminescent materials with high concentrations of transition metal or rare earth ions must face the problem of reducing the concentration quenching of luminescence. This process, which causes a relevant lowering of luminescence efficiency, is mainly caused by cross-relaxation mechanisms that allow the excitation energy to be transferred through one or two mid-levels of donor-acceptor pair of identical sites, increasing the probability of non-radiative energy migration to non-radiative quenching sites. With a small energy gap between the metastable and the nearest lower levels of activator, the luminescence quantum yield can also be significantly reduced by intracenter non-radiative decay processes mediated by vibrations of molecular groups within the first coordination shell of the ions. In glasses, where the efficiency of exchange, cross-relaxation and non-radiative energy migration processes is generally higher than in crystals, the luminescence of transition metal ions and, to a lesser extent, of rare earth ions is quenched at too large a concentration of active ions, preventing the development of integrated optical amplifiers and, in most cases, the use itself of glasses as active optical media. On the other hand, the development of glass-based optical media is strategic for the design of new stable and robust devices in a continuously growing number of applications.

Glass production technology

It is worth noting that studies at SILG are aimed not only to investigate structural and physical properties of new functional glass compositions, but also to identify technologically sustainable processes for material production on the semi-industrial scale. This aim is pursued by means of pilot production lines suitable to test and improve process conditions directly deliverable to industry, and to produce material in pre-industrial amount. As a matter of fact, the vast majority of studies in the field of functional glasses do use samples of reduced size in the form of thin plates obtained by melt quenching. The latter approach, usually dictated by relevant costs of reagents and platinum equipments in the case of large scale production, tends to underestimate glass crystallization problems in real technological processes, as well as important issues related to stability and reproducibility of material properties. By contrast, light-emitting glass and nanostructured glassceramics produced at SILG according to the expected requirements of homogeneity and reproducibility [1] are suitable for prompt commercialization.

Strategies about structure and composition

Two lines of research at SILG are devoted to the investigation of new solutions in the field of light-emitting glass-based materials. These lines - including nanostructured glassceramics with transition metal ions and rare earth doped glasses - follows two different strategies:

  1. Formation of nanocrystals in oxide glasses, combining in one material optical properties of a crystalline phase doped with transition metal ions and benefits of a glassy matrix.
  2. Formation of huntite-like coordination structures in glass, taking advantage of the structural constraints on the minimum ion-ion distance in lanthanide aluminoborate to reduce ion-ion energy transfer in rare earth doped glass.

In the first case, nano-inhomogeneous glasses can be obtained at the initial stages of the amorphous phase separation. This approach is important for the simple reason that many crystalline phases, including metastable ones, are difficult or impossible to obtain in the form of a single crystal but can precipitate as nanocrystals in a glassy matrix. As a result of the structural peculiarities of alkali gallium germanosilicate glasses, first studied at SILG [2-13], light-emitting ions, as Ni2+, can be selectively incorporated into the nanocrystals giving unprecedented luminescence properties to the nanostructured glass. It is possible to control the optical properties of the material by varying the volume fraction of nanoparticles in the glass, their size and structure. This opens up new possibilities for the fabrication of laser and fluorescent media. In Fig. 1 TEM images are reported, showing dispersion and crystalline structure of ?γ-Ga2O3 nanocrystals obtained in Ni2+-doped glass.

Fig. 1. (a) Transmission electron microscopy image of a sample of nanostructured 7.5Li2O-2.5Na2O-20Ga2O3-35GeO2-35SiO2 glass, showing the dispersion of segregated nanoparticles. (b) High-resolution TEM image of a single nanoparticle evidencing crystalline features consistent with Ga2O3- phases.

In the second case, the synthesis of glasses with chemical composition similar to huntite-like LnAl3(BO3)4 crystal is aimed to reproduce in glass the coordination structure typical of the crystalline phase. Huntite crystals are indeed characterized by a large minimum distance Ln-Ln ( 5.9 angstrom), which keeps low the probability of cross-relaxation and cooperative quenching of luminescence. As a matter of fact, the incongruent melting character of huntite-like crystals makes it difficult to obtain single crystals suitable for practical applications. On the other hand, glassceramics with rare earth aluminoborate crystals are known for their nonlinear optical properties due to noncentrosymmetric structure. The investigation at SILG achieved the goal of obtaining huntite-like glassy phases with the expected coordination characteristics of crystal in combination with the flexibility of glass technology. The glass system Ln2O3-Al2O3-B2O3, particularly near huntite stoichiometry, is now studied as a promising system for the fabrication of small multifunctional laser media.

Nanostructured germanosilicates and the role of Ga-oxide nanocrystals

The investigation of gallium germanosilicate glasses at SILG has given for the first time a comprehensive view of the relationship between spectral properties and nanostructuring in this system, both in undoped and in NiO-doped variants, also suggesting a scheme of the structural changes taking place in this compound [5]. Essential issue for achieving these outcomes was the access to a multiplicity of complementary experimental techniques for the physical and structural characterization of materials - including x-ray diffraction, small-angle neutron scattering, transmission electron microscopy, Raman scattering, infrared spectroscopy, x-ray fluorescence analysis - together with a detailed spectroscopic investigation, comprising optical absorption, photoluminescence spectroscopy, and time resolved luminescence analysis. Such a comprehensive knowledge on the structural and optical properties of gallium germanosilicate glasses is an original achievement of investigations at SILG. The resulting nanostructured glasses, whose applications are being patented, show a wide range of luminescence properties from UV to the near infrared region, tunable by changing the composition. As regards application in the field of broadband infrared light emitting material, we obtain bandwidth of more than 300 nm with a maximum at 1300 nm (Fig. 2).

Fig. 2. Absorption (left) and luminescence (right) spectra of gallium germanosilicate as-quenched (dark red curve) and heat-treated (green curve) glasses doped with Ni2+ [2].

During the period 2010-2012, the experimental activity on gallium germanosilicate glasses at SILG has also been devoted to the investigation of melting, formation and annealing conditions, including the study of Ni2+ doped variants and the influence of component volatilization during melting. SILG produced the first example in the world of gallium germanosilicate glass with optical quality, in which Ga2O3 nanocrystals can be created by a suitable thermal activation of the glass - with controlled size and selectively doped by light-emitting ions. This material combines optical homogeneity on the macro- and micro-scale and advanced light-emission properties in a stable glassy material with a melting temperature lower than 1500°. Preforms from this material were drawn at the Fiber Optics Research Center at the General Physics Institute of the Russian Academy of Sciences obtaining prototypes of novel nanostructured optical fibers.

Further work on gallium germanosilicates is in progress along four directions:
     - investigation of new compositions for the fabrication of nanostructured fibers and fiber glass cladding for tunable lasers and fiber amplifiers in the near infrared range, including Bi-doped glasses.
    - elaboration of new conditions of melting, formation and heat treatment for the synthesis of undoped gallium germanosilicate glass for the design of UV-radiation converters to enhance the sensitivity of CCD detectors in the UV range, and sensors of invisible sparks, flames, and electric dispersion in safety applications.
    - fabrication of light converters from nanostructured glasses doped with d-and f-elements for two-component LED white-light sources for home and industrial lighting, sensor technology, biomedical applications, offering in these field potential improvement as regards cheapness, reliability and chemical resistance.
    - implementation of photo-activated nanostructuring process in the development of germanosilicates with unprecedented photosensitivity for the functionalization of glass-based devices such as optical fiber sensors based on Bragg gratings.

Huntite-like doped glasses and the role of concentration quenching

In the framework of the investigation aimed at the reduction of concentration quenching of luminescence in light-emitting materials [14-29], SILG activity comprised the production and the spectroscopic study of glasses with the composition of huntite-like (Sm,Y)Al3(BO3)4 crystal (Figs. 3, 4). This line of research began from the comparison of spectral and kinetic characteristics of photoluminescence between glass and polycrystalline samples with equal composition as a function of Sm content. This investigation gave information on the concentration dependence of the quantum yield of Sm3+ luminescence, and additional previously unknown data about other important parameters, including the upper limit of quantum yield, the luminescence branching coefficients, the cross section of stimulated emission, and microparameters of donor-acceptor interaction [14]. All these data enabled a preliminary calculation of laser pump conditions to be used for tests technological applications.

    
Fig. 3. Luminescence spectrum of huntite-like glass doped with 1 mol. % Sm 2O3 excited at 404 nm. Fig. 4. Rod of glass with composition 10(Sm0,3Y0,7) 2O3-30Al22O3-60B2O3 mol.% at day-light (upper) and UV-light (low).

The analysis of the spectroscopic data demonstrates the possibility to obtain glass with unprecedented large value of the minimum distance between light-emitting ions (0.67 nm), even greater than in huntite crystals (0.59 nm). Glasses produced at SILG show indeed luminescence quantum yield higher than in polycrystals up to samarium concentration of 1.01020 cm3. The latter outcome is related to a weaker intracenter luminescence quenching compared with crystalline huntite-like aluminoborate. In fact, different boron coordination from crystal to glass - from only three-fold to three- and four-fold coexistent coordinations - and specific procedure to avoid composition hydration during melting eventually give a structure with reduced coupling of local phonon modes with the electronic excitation. The material finally optimized at SILG - also in form of rods more than 10 cm long - is characterized by resistance to crystallization and by lack of cords and bubbles, with features suitable for optical applications and for the production of fibers.

Further work on huntite-like glasses is in progress along four directions:

   - Experiments at the laboratory of semiconductors physics and technology at the B.I. Stepanov Institute of Physics NASB demonstrated light-emission gain in this glass from Sm3+ luminescence corresponding to the transitions 4G5/26H7/2 ( ≈ 600 nm) and 4G5/26H9/2 (λ ≈ 650 nm), by optical pumping in the transition 6H5/263/2 (λ = 402 nm). The study of a prototype of enhanced miniconverter based on the gain of the 600 nm emission pumped at 470 nm is in progress.

   - The fabrication of a two-component light emitter is planned in collaboration with experts in the field of photosynthesis (Biological Center, Pushchino). As a matter of fact, the emission spectrum of Sm3+ ions lies in the region of maximum spectral efficiency of photosynthesis, potentially interesting for agriculture applications. The design includes blue LED and superluminescent converter based on huntite-like Sm-glass, working within two (blue and red) peaks of photosynthetic activity.

   - Glass production at SILG also includes huntite-like glasses codoped with Ce3+ and Tb3+. In this glass the quantum yield of Tb3+ luminescence, sensitized by Ce3+ ions, is approximately 80% (Fig. 5, 6), and almost unaffected by concentration quenching. Synthesized glasses are characterized by high absorption in the ultraviolet region and high luminescence efficiency at the maximum of human eye sensitivity spectrum [20-22]. The spectral features are currently investigated for possible applications in biomedical fluorescence spectroscopy.

   - (TbxCe1-x)2O3-Al2O3-B2O3-Sb2O3 glasses are investigated as cathodophosphor in form of bulk samples and powders to monitor electron beams. Installation of bench for cathodoluminescent studies is planned in 2013.

   - extension of the range of applications of huntite-like glass to Eu-doped variants is also investigated. At present, preliminary studies are in progress based on the crystal field analysis of spectroscopic data on polycrystalline EuAl3(BO3)4 powders [23]. This analysis suggests that lasing is possible only exciting the Eu3+ transition 5D05F4 at about 700 nm. The results also explain previous data on unexpected low luminescence yield by electron beam excitation [29].

   - Fundamental studies are also planned to collect further details on the coordination structure in huntite-like glasses by means of high resolution neutron diffraction, using samples with different isotopic compositions of samarium, fine determination of the BO3/BO4 ratio by NMR, detailed study of glass structure by means of vibrational spectroscopy.

    
Fig. 5. Spectra of (1) light attenuation, (2) luminescence and (3) luminescence excitation for the glass doped with (mol. %) 2Ce2O3, 4Tb2O3 and 2Sb2O3. Fig. 6. Photo of the investigated glass under UV-irradiation at λ=365 nm..

Publications

1. E.Kh. Mamadzhanova "Spectral-kinetic properties of activated by rare earth elements glasses of Y2O3-Al2O3-B2O3 system and polycrystals with huntite-like structure". Extended abstract of PhD dissertation // MUCTR, oscow, 2012, p. 16.

2. V.N. Sigaev, N.V. Golubev, E.S. Ignat'eva, V.I. Savinkov, M. Campione, R. Lorenzi, F. Meinardi and A Paleari "Nickel-assisted growth and selective doping of spinel-like gallium oxide nanocrystals in germano-silicate glasses for infrared broadband light emission" Nanotechnology 23 (2012) 015708 (7pp).

3. V.M. Mashinsky, N.M. Karatun, V.A. Bogatyrev, V.N. Sigaev, N.V. Golubev, E.S. Ignat'eva, R. Lorenzi, M. Mozzati, A. Paleari and E.M. Dianov "Microfluorescence Analysis of Nanostructuring Inhomogeneity in Optical Fibers with Embedded Gallium Oxide Nanocrystals" Microscopy and Microanalysis 18 (2012) pp. 259-265.

4. Application for an invention RU 2012110802/20 22.03.12. Glass-ceramic material, authors: N.V. Golubev, .S. Ignat'eva, V.I. Savinkov, V.N. Sigaev, P.D. Sarkisov.

5. V.N. Sigaev, N.V. Golubev, E.S. Ignat'eva, B. Champagnon, D. Vouagner, E. Nardou, R. Lorenzi, A. Paleari. Native amorphous nanoheterogeneity in gallium germanosilicates as a tool for driving Ga2O3 nanocrystal formation in glass for optical devices. Nanoscale (submitted).

6. E.S. Ignat'eva, N.V. Golubev, V.N. Sigaev. "Crystallization of galliumsilicagermanate glasses doped by NiO". UCChT-2012, MUCTR, Moscow.

7. E.S. Ignat'eva, N.V. Golubev, V.N. Sigaev, B. Champagnon, D. Vouagner, E. Nardou, R. Lorenzi, A. Paleari. "Nanocrystallization processes in Me2O-Ga2O3-SiO2-GeO2-NiO glasses (Me=Li and Na)" // 10th International Symposium on Crystallization in glasses and Liquids (September 23-26, 2012, Goslar, Germany).

8. V.N. Sigaev, N.V. Golubev, E.S. Ignat'eva, V.I. Savinkov, R. Lorenzi, F. Meinardi, M. Campione, A. Paleari. The role of nickel additives in growth of LiGa5O8 nanocrystals in germanosilicate glasses // Proceedings of the first International meeting "Trends in oxide materials - functions and structure between glasses and crystals", MUCTR, Moscow, March 29-31, 2011, pp. 138-151.

9. N.V. Golubev, E.S. Ignat'eva, V.I Savinkov, V.N. Sigaev, A. Paleari, V.G. Plotnichenko, V.M. Mashinsky, E.M. Dianov. Ni2+-doped nanostructured glasses for broadband near-infrared luminescence // Proceedings of the first International meeting "Trends in oxide materials - functions and structure between glasses and crystals", MUCTR, Moscow, March 29-31, 2011, pp. 35-41.

10. N.M. Karatun, C, V.A. Bogatyrev, E.M. Dianov, N.V. Golubev, E.S. Ignat'eva, V.N. Sigaev. Fiber waveguide with galliumgermanosilicate glass-ceramic core doped with NiO // Proceedings of the 10th All-Russian Conference with an elements of scientific school conference for young scientists "Materials of nano-, micro- and optoelectronics and fiber optics: physical properties and applications". Saransk, October 4-7, 2011, p. 134.

11. N.V. Golubev, A. Paleari, E.S. Ignat'eva, V.I. Savinkov, V.N. Sigaev. NiO doping effects on the nanostructuring of gallium silica-germanate glasses - structural and optical features // Conference materials E-MRS 2011 FALL MEETING September 19-23, 2011, Warsaw University of Technology, Poland.

12. E.S. Ignat'eva, N.V. Golubev, . Paleari, V.N. Sigaev. Near infrared luminescence of galliumgermanosilicate glasses doped with NiO // United Congress of Chemical Technology of Youth " UCChT-2011", November 8-13, MUCTR, Moscow, pp. 86-88.

13. N.V. Golubev, V.I Savinkov, E.S. Ignat'eva, S.V. Lotarev, P.D. Sarkisov, V.N. Sigaev, L.I. Bulatov, V.M. Mashinsky, V.G. Plotnichenko, E.M. Dianov. Nickel-doped gallium-containing glasses luminescent in the near-infrared spectral range. Glass Physics and Chemistry 2010, Vol. 36, No. 6, pp. 657-662.

14. G.E. Malashkevich, V.N. Sigaev, N.V. Golubev, E.Kh. Mamadzhanova, A.A. Sukhodola, A. Paleari, P.D. Sarkisov, A.N. Shimko. Spectroscopic properties of Sm-containing yttrium-aluminoborate glasses and analogous huntite-like polycrystals. Materials Chemistry and Physics (2012).

15. E.Kh. Mamadzhanova, N.V. Golubev, V.N. Sigaev, G.E. Malashkevich, A.N. Shimko, I.V. Prusova, I.I. Sergeev. Crystallization and luminescence properties of (SmY1-)2O3 Al2O3 B2O3 glasses. Glass and ceramics (2012).

16. E.Kh. Mamadzhanova, N.V. Golubev, V.N. Sigaev. Glass phase separation in system Sm2O3-Y2O3-Al2O3-B2O3 // IV All-Russian Conference on Chemical Technology with international participation (ChT'12). A.N. Frumkin Institute of Physical Chemistry and Electrochemistry and Semenov Institute of Chemical Physics. Moscow, March 18-23, 2012. Book of Abstract. pp. 132-135.

17. G.E. Malashkevich, V.N. Sigaev, E.Kh. Mamadzhanova, N.V. Golubev, E.V. Lutsenko, N.V. Rzheutsky, M.S. Leonenya, A.N. Shimko, G.P. Yablonsky. Luminescence and lasing characteristics of (SmxY1-x)2O3 B2O3 Al2O3 glasses // Proceedings of the IX International Conference "Laser Physics and Optical Technologies", Grodno, May 30-June 2, 2012, p. 109.

18. G.E. Malashkevich, V.N. Sigaev, E.Kh. Mamadzhanova, N.V. Golubev, E.V. Lutsenko, N.V. Rzheutsky, M.S. Leonenya, A.N. Shimko, G.P. Yablonsky. Spontaneous and stimulated emission of (SmxY1-x)2O3 B2O3 Al2O3 glasses // Proceedings of the IX International Conference "Laser Physics and Optical Technologies", Grodno, May 30-June 2, 2012, (in press).

19. Application for an invention RU 2012107045 27.02.2012. Luminescent silica glass, authors: G.E. Malashkevich, A.G. Malashkevich, V.N. Sigaev. Application for an invention BY 20111520 16.11.2011.

20. Application for an invention BY 20121190 10.08.2012. Luminescent glass (variants), authors: G.E. Malashkevich, V.N. Sigaev, N.V. Golubev, E.Kh. Mamadzhanova, T.G. Hotchenkova.

21. G. Malashkevich, V. Sigaev, N. Golubev, E. Mamadzhanova, T. Khottchenkova, A. Stupak, A. Sukhodola. Spectral-luminescent properties of Y2O3 B2O3 Al2O3 Sb2O3 glasses doped with Ce and Tb // 8th International Conference on f-elements 26-31 August 2012. Udine, Italy). Book of Abstract. ORAL TALKS, OPT 22O.

22. G.E. Malashkevich, V.N. Sigaev, N.V. Golubev, E.Kh. Mamadzhanova, T.G. Hotchenkova, I.V. Prusova. UV radiation imaging by glasses of system (CexTbyY1-x-y)2O3-B2O3-Al2O3-Sb2O3 // Proceedings of the 11th All-Russian Conference with an elements of scientific school conference for young scientists "Materials of nano-, micro- and optoelectronics and fiber optics: physical properties and applications", Saransk, October 2-5, 2012.

23. E.G. Malashkevich, A.A. Kornienko, E.B. Dunina, V.N. Sigaev et al. Probabilities of absorption transitions from Eu3+ metastable state in EuAl3(BO3)4 huntite-like polycrystals. Journal of Luminescence, 2012.

24. G.E. Malashkevich, A.A. Sukhadola, I.I. Sergeev, I.V. Prusova, D.A. Goshko, N.V. Golubev, E.Kh. Mamadzhanova, V.I. Savinkov, P.D. Sarkisov, V.N. Sigaev, Luminescence of huntite polycrystalls and huntite-like glasses activated with Sm3+ ions // Proceeding of the 1st International Meeting "Trends in oxide materials-functions and structure between glasses and crystals". MUCTR, Moscow, March 29-31, 2011, pp. 42-52.

25. Patent RU 2415089 "Luminescent glass" authors: G.E. Malashkevich, V.N. Sigaev, N.V. Golubev, E.Kh. Mamadzhanova, P.D. Sarkisov. Patent BY 14839.

26. E.Kh. Mamadzhanova, N.V. Golubev, G.E. Malashkevich, V.N. Sigaev. Luminescent huntite-like glasses activated by Sm3+ // UCChT-2011, MUCTR, Moscow, pp. 97-101.

27. G.E. Malashkevich, A.A. Sukhadola, V.N. Sigaev, P.D. Sarkisov, N.V. Golubev, E.Kh. Mamadzhanova. Spectral-luminescence properties and interaction between Sm3+ in silica and huntite-like glasses // III Congress of Belarusian Physicists (in the framework of the congress - symposium in honor of F.I. Fedorov 100th Anniversary), Minsk, September 25-27, 2011: Book of Abstract. p. 34.

28. G.E. Malashkevich, V.N. Sigaev, N.V. Golubev, E.Kh. Mamadzhanova, E.V. Petryakov, A.A. Sukhadola, I.I. Sergeev. Spectral-luminescence properties of huntite-like and silica glasses activated by Sm3+ // Proceedings of the 10th All-Russian Conference with an elements of scientific school conference for young scientists "Materials of nano-, micro- and optoelectronics and fiber optics: physical properties and applications", Saransk, October 2-5, 2012, p. 68.

29. G.E. Malashkevich, V.N. Sigaev, N.V. Golubevb, E.Kh. Mamadzhanova, A.V. Danil'chik, V.Z. Zubelevich and E.V. Lutsenko. Rearrangement of optical centers and stimulated radiation of Eu3+ in polycrystalline huntite under optical and electron beam excitation. JETP Letters, 2010, Vol. 92, No. 8, pp. 497-501.