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In this paper structural, thermal and optical properties of Er3+ doped germanate glasses with the composition of 63.0GeO2-9.8Ga2O3-11.1BaO-4.9X-8.8Na2O-2.5Er2O3 (in mol%), where X = ZnO, TiO2, Al2O3 and Y2O3 are reported. The investigated glasses exhibit low phonon energies (-1) and high glass transition temperature varying between 588 and 642 °C. The Raman spectra evidence about different polymerization degree of the glasses. The thermal treatment leads to the precipitation of various crystals, the composition of which depends on the glass composition. According to the spectroscopic properties Er3+ ions are suspected to have similar local environment in the as-prepared glasses. However, Er-doped crystals are expected to precipitate upon devitrification, which leads to significant change of the spectroscopic properties, in particular increase in the intensity of upconversion and MIR emissions is observed. It is demonstrated that the glasses with Y2O3, ZnO and TiO2 are promising glasses especially for MIR applications.

International audience; Since the invention and further development of lasers in the 1960s, photonics has grown into a field that permeates virtually every aspect of modern life. As photonics deals with the generation, transmission, modulation, amplification, conversion, and detection of light, glasses have played crucial and central roles in a multitude of applications given glasses' diverse range of composi-tions, properties, and forms. They are also low-cost materials, recyclable and generally easy to fabricate. In homage to the United Nations International Year of Glass 2022, this paper reviews the past, present, and future of photonic glasses.

International audience; Hackmanites are reusable and non-toxic materials for radiochromic films. They show a unique “gamma memory” function where the width of the reflectance spectrum changes permanently, but the ability to change color reversibly remains fully functional.

Using three-dimensional (3D) second-harmonic generation (SHG) scanning microscopy, we unravel the formation and distribution of distinct and highly localized persistent luminescent (PeL) microparticles of varied hierarchical levels in glasses prepared using the direct doping method. The PeL microparticles were added in the glasses at different doping temperatures and the glasses were quenched after different dwell time. The SHG maps of the PeL microparticles in the glass, prepared with a doping temperature of 975°C and a dwell time of 3 min, reveal grating-like microscopic domains. This suggests that a large arrangement of PeL crystals spanning several micrometers in three dimensions is manifested by the imbued PeL microparticle. In contrast, the SHG maps of the PeL microparticles inside the glass prepared at doping temperature of 1025°C and dwell time of 10 min, show the existence of single, highly localized and most importantly, submicrometer-sized PeL crystals. These findings substantiate well with the expected behavior of the PeL microparticles in glasses and their physical disintegration in the form of nanoparticles at high doping temperatures and dwell times. The SHG microscopy technique is shown to circumvent the fundamental challenges of traditional and usually destructive imaging methods to detect and visualize PeL nanoparticles in a glass matrix and expected to open a new avenue to evidence the presence of crystals in glasses. publishedVersion

In homage to the United Nations International Year of Glass 2022 (IYoG 2022), this article discusses the past, present, and future of glass education, with a focus on inorganic systems of value to optical and photonic applications.

Nanosized hydrated YbPO4·nH2O powders were prepared by precipitation from aqueous solutions. It is shown that the structure, optical properties, and size of the raw particles can be further tailore...

With this chapter, our goal is to highlight important research topics in which biophotonics will play a crucial role in the near future. Biophotonics offers tremendous opportunities for applied and fundamental research and has been successfully used for early disease detection and for light-guided/activated therapies. However, there is still an urgent need for the development of a material platform for biophotonic applications, especially biocompatible and biodegradable materials with optimized biological, chemical, optical and mechanical properties. Phosphate glasses are clearly promising biophotonic materials and their use opens the path to the development of clinically relevant biophotonic devices for in vitro optical techniques to be used in situ and in vivo. These new phosphate glasses could be used not only for early detection of diseases but also for effective targeted therapies. They could also re-establish impaired biological functions. We expect these new materials to have a significant influence on the development of new technologies, offering huge commercial rewards worldwide.

The radiation effects of electrons and protons on the spectroscopic and optical properties of oxide glasses doped with Yb

New Yb3+-doped phosphate glasses with a composition of (98.75-x) (90 NaPO3 – 10 Na2O) – x (Al2O3, TiO2, or ZnO) – 1.25 Yb2O3 (in mol-%), with x from 0 to 3, were prepared via conventional melting and quenching process. The thermal and physical properties were studied by differential thermal analysis (DTA) and density measurement, respectively. The glass structure was investigated using visible/infrared spectroscopy and the crystallization properties of the glasses using XRD. Changes in the glass composition were found to have an impact on the glass structure and more importantly on the crystallization process; the addition of Al2O3, TiO2 and ZnO promotes the precipitation of the Na5P3O10 crystalline phase at the expense of NaYb(P2O7) and NaPO3 phases and more importantly, promotes surface crystallization at the expense of bulk crystallization. publishedVersion

Er3+ doped phosphate glasses with the composition 75NaPO3-25CaF2 (mol%) were prepared at different melting temperatures to demonstrate the importance to quantify the fluorine content when preparing oxyfluoride glasses. Indeed, increasing the melting temperature from 900 to 1000 °C leads to a small reduction in the fluorine content from 9.4 at % to 8.8 at % as quantified using EPMA. Whereas this loss of fluorine can be suspected from small changes in the thermal properties of the glass, it increases significantly the glass crystallization tendency in this glass system. This means that a heat treatment of the as-prepared glass should be performed when evaporation of fluorine during the glass melting is suspected. Sample preparation for the characterization of the spectroscopic properties of the glasses is discussed here as well; bulk glasses should be used when measuring the spectroscopic properties of oxyfluoride glasses, which are known to be hygroscopic. It is shown, in this work, that a heat treatment of the glass within the investigated glass system leads to transparent glass-ceramics with volume precipitation of Er3+ doped CaF2 crystals with strong upconversion.

Strong persistent luminescence (PeL) from silica bodies was obtained, for the first time, by sintering silica powder mixed with PeL SrAl2O4:Eu2+,Dy3+ microparticles (MPs). We show that it is not possible to prepare transparent PeL silica glass due to the decomposition of the MPs, which occurs already at 1450 °C. The MPs decomposition was associated with the precipitation of Sr3Al10SiO20 phase when sintering up to 1650 °C and of SrAl2Si2O8 when sintering between 1650 and 1750 °C. Cristobalite was found to also precipitate when sintering for 10 min but has no impact on the PeL of the bodies.

Recently, a phosphate glass with composition 20 CaO-20 SrO-10 Na2O-50 P2O5 (mol%) was found to have good potential as a biomaterial and to possess thermal properties suitable for fiber drawing. This study opened the path towards the development of fully bioresorbable fibers promising for biosensing. In the past, this phosphate glass with CeO2 was found to increase the refractive index and the glass stability. Therefore, a new SrO-containing glass was prepared with 1 mol% of CeO2 and core fibers were drawn from it. A core-clad fiber was also processed, where the core was a Ce-doped glass and the clad undoped, to allow for total internal reflection. The mechanical properties of the core and core-clad fibers are discussed as a function of immersion time in TRIS-buffer solution. Finally, a sensing region was created, in the core-clad fiber, by etching the cladding using phosphoric acid. Then, the change in light transmission, upon immersion in TRIS-buffer solution, was quantified to assess the potential use of the novel core-clad fiber as a biosensor. Upon immersion in TRIS, the core-clad fiber was found to guide light effectively and to maintain a tensile strength of ~150–200 MPa up to 6 weeks in TRIS, clearly showing that this fiber has potential as a biosensing device. acceptedVersion

We introduce the Optical Materials Express feature issue that celebrates historic and recent advances in optical glass. In honor of the United Nations declaring 2022 to be the International Year of Glass (IYOG), this issue comprises a collection of twenty-seven manuscripts that highlight processing, characterization/metrology and applications where glass has changed our world.

The influence of the addition of Y2O3 on the structural, spectroscopic, and laser properties of newly prepared Er, Yb-doped strontium-sodium phosphate glass was investigated. While the addition of Y2O3 has a small influence on the absorption spectra and fluorescence lifetime, it has a strong impact on the emission cross-section and on OH− content. The glasses were used as the active medium for diode-pumped laser emitting at 1556 nm. The increase in Y2O3 content leads to a significant 35% increase in laser slope efficiency up to 10.4%, but at the expense of the substantial reduction of the wavelength tunability from 82 to 54 nm.

The influence of the addition of Y2O3 on the structural, spectroscopic, and laser properties of newly prepared Er, Yb-doped strontium-sodium phosphate glass was investigated. While the addition of Y2O3 has a small influence on the absorption spectra and fluorescence lifetime, it has a strong impact on the emission cross-section and on OH− content. The glasses were used as the active medium for diode-pumped laser emitting at 1556 nm. The increase in Y2O3 content leads to a significant 35% increase in laser slope efficiency up to 10.4%, but at the expense of the substantial reduction of the wavelength tunability from 82 to 54 nm.

The preparation of tellurite glasses with persistent luminescence by adding persistent luminescent particles in the glass melt is reported. Compared to phosphate glasses, the afterglow from the tellurite glasses is low, indicating that the tellurite melt is more corrosive on the particles than the phosphate melt. However, as opposed to phosphate glasses, no emission from Eu3+ was detected in the photoluminescence spectra of the glasses when crushed into powder. We show that a confocal Raman microscope can be used to evidence the presence of Eu3+ in the glass-particles interface confirming that some oxidation of Eu2+ actually takes place during the preparation of the tellurite glasses. publishedVersion

In this paper, the impact of the post-heat-treatment on the structural and spectroscopic properties as well as on the chemical durability of a thermally stable Er3+-doped phosphate glass in the system P2O5 - K2O - Al2O3 - B2O3 - BaO - PbO - La2O3 - Gd2O3 is reported. Two crystalline phases, namely La, Gd-monazite and AlKP2O7, were found to precipitate from the surface of the glass after heat-treatment, as confirmed by both X-ray Diffraction (XRD) and Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX) analyses. Moreover, the heat-treatment was responsible for the formation of a more polymerized glass network close to the surface crystalline layer as evidenced using micro-Raman spectroscopy. From the changes in the Er3+ optical properties, some of the Er3+ ions are suspected to enter in the crystals. Both the as-prepared and heat-treated glasses were subjected to a degradation test in hydrochloric acid (HCl) and showed a congruent and incongruent dissolution behavior, respectively.

The role of fluorine in bioactive glasses is of interest due to the potential of precipitating fluorapatite, a phase with higher chemical resistance than the typical hydroxyapatite precipitated from oxide bioactive glasses. However, the introduction of fluorine in silicate bioactive glasses was found deleterious to the bioactivity of the glass. Here, phosphate glasses with the composition 75NaPO3-(25-x) CaO-xCaF2 (in mol%), with x = 0–20 and glass-ceramics were investigated to evaluate their potential as substitutes to the traditional silicate bioactive glass. An increase in CaF2 substitution for CaO led to an increase in the glass solubility, due to an increase in highly soluble F(M)n species (where M is a cation) and to an increased polymerization of the phosphate network. Structural analysis reveals the formation of F P bonds, in addition to the F(M)n species, in the glass with the higher CaF2 content. Furthermore, with heat treatment, CaF2 crystals precipitate within the bulk in the newly developed glass, when x = 20. This bulk crystallization reduces the glass dissolution without compromising the precipitation of a reactive layer at the glass surface. Finally, in vitro cell tests were performed using MC3T3 pre-osteoblastic cells. While the substitution of CaF2 for CaO led to an increased cytotoxicity, the controlled crystallization of the fluorine containing glasses decreased such cytotoxicity to similar values than traditional bioactive phosphate glass (x0). This study reports on new oxyfluorophosphate glass and glass-ceramics able, not only, to precipitate a Ca-P reactive layer but also to be processed into glass-ceramics with controlled crystal size, density and cellular activity. Statement of significance Uncontrolled crystallization of bioactive glasses has negative effect on the materials' bioactivity. While in silicate glass the bioactivity is solely reduced, in phosphate glasses it is often completely suppressed. Furthermore, the need for fluorine containing bioactive glasses, not only for use in bone reconstruction but also in toothpaste as emerged. The addition of F in both silicate and phosphate has led to challenges due the lack of Si-F or P-F bonds, generally leading to a decrease in bioactivity. Here, we developed a bioactive invert phosphate glass where up to 20 mol% of CaO was replaced with CaF2. In the new developed glasses, NMR demonstrated formation of P-F bonds. The content of fluorine was tailored to induce CaF2 bulk crystallization. Overall an increase in F was associated with an increase network connectivity. In turns it led to an increased dissolution rate which was linked to a higher cytotoxicity. Upon (partial to full) surface crystallization of the F-free glass, the bioactivity (ability to form a reactive layer) was loss and the cytotoxicity again increased due to the rapid dissolution of one crystal phase and of the remaining amorphous phase. On another hand, the controlled bulk precipitation of CaF2 crystals, in the F-containing glass, was associated with a reduced cytotoxicity. The new oxyfluorophosphate glass-ceramic developed is promising for application in the biomedical field.

Yb3+ doped oxyfluorophosphate glasses with the composition (98.75) [90NaPO3-(10-x) Na2O-xNaF] - 1.25Yb2O3 (in mol%) with x = 0, 2.5, 5, 7.5 and 10 were prepared using a standard melting process. The progressive replacement of Na2O by NaF leads to an increase in the number of Q2 units at the expense of the Q1 units. This increase in the polymerization of the glass network leads to a shift of the optical band gap to lower wavelength, to a slight increase in the intensity of the emission at 1000 nm and more importantly to a change in the glass crystallization process. Indeed, both surface and bulk crystallization were observed in the glass with x = 0 while surface crystallization only occurs when NaF is added in the phosphate network. The heat treatment leads to the precipitation of at least three crystalline phases: as x increases, the NaPO3 phase grows at the expense of Na5P3O10. All glasses precipitate the Yb containing crystal, NaYbP2O7 which leads to an increase in the intensity of the emission at 1000 nm compared to the emission at 975 nm. We show for the first time to the best of our knowledge that transparent Yb3+ doped phosphate glass-ceramics can be obtained within this glass system when free of NaF. acceptedVersion

International audience; Bioactive fibers have become increasingly prevalent for applications in optical sensing and as reinforcement in fully biodegradable devices. However, the typical bioactive glass fibers drawn from silicate glasses have poor mechanical properties. Here, we present our latest study on the development of new bioactive single-core (SC) borophosphate fiber with the composition (in mol%) 47.5P(2)O(5)-20CaO-20SrO-10Na(2)O-2.5B(2)O(3) and of core-clad (CC) borophosphate fiber, the composition (in mol%) of the clad and the core being 47.5P(2)O(5)-20CaO-20SrO-10Na(2)O-2.5B(2)O(3) and 0.025CeO(2)-0.975(47.5P(2)O(5)-20CaO-20SrO-10Na(2)O-2.5B(2)O(3)), respectively. We show that the immersion in aqueous solutions such as Tris(hydroxymethyl)aminomethane (TRIS) increases first the mechanical properties of the fibers due to the early congruent glass dissolution and so due to the reduction in the density of surface flaws. However, for long immersion in TRIS or in Simulated Body Fluid (SBF), the mechanical properties decrease due to the precipitation of a reactive calcium-phosphate layer at the surface of the fibers. Especially when immersed for a long time in SBF, the fibers become too fragile to allow one to measure their mechanical properties. Nonetheless, we clearly show in this study that the newly developed fibers are promising materials for reinforcing composite and/or as biosensors as these fibers still possess sufficiently high mechanical properties after immersion for significant time in SBF and/or TRIS.

V.V. acknowledges the financial support of ERDF PostDoc project No. 1.1.1.2/VIAA/3/19/440 (University of Latvia Institute of Solid State Physics, Latvia) and LP the Academy of Finland (Flagship Programme, Photonics Research and Innovation PREIN 320165 and Academy Project -326418) for the financial support. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01- 2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART 2 ., SrAl2O4: Eu, Dy, B particles were added in a phosphate glass (90NaPO3-10NaF (in mol%)) using the direct doping method. For the first time, the composition of the particles prior to and after embedding them in the glass was analysed using EPMA analysis. Boron was found to be incorporated in already distorted surroundings creating new trapping centers in the particles which are thought to be favourable for the tunnelling process and so for the afterglow at 10K. Despite the partial decomposition of the particles, the glass exhibit afterglow at low temperature confirming to be promising materials for low temperature applications., ERDF 1.1.1.2/VIAA/3/19/440; LP the Academy of Finland 320165 and 326418; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017 TeamingPhase2 under grant agreement No. 739508, project CAMART²

Novel NaYF4:Yb3+, Er3+ nanocrystals containing phosphate glass with composition 83.25NaPO3–9.25NaF-5ZnO-2.5Ag2O (in mol%) was prepared by adding the NaYF4:Yb3+, Er3+ nanocrystals in the glass using the direct doping method. The optical and luminescence properties of this new glass are presented and discussed. The newly developed glass exhibits visible emission under 980 nm pumping with high intensity confirming the presence of the NaYF4:Yb3+, Er3+ nanocrystals in the glass. From the absorption spectrum of the as-prepared glass, it is showed that the as-prepared glasses contains already Ag nanoparticles which are thought to precipitate due to the decomposition of some of the NaYF4:Yb3+, Er3+ nanocrystals occurring during the glass preparation. A heat treatment of the glass was found to lead to the migration of Ag species at the surface of the glass as evidenced using SEM and to a decrease of the intensity of the upconversion mostly due to an increase of the inter defects in the NaYF4:Yb3+, Er3+ nanocrystals due to the heat treatment. acceptedVersion

We introduce the use of second-harmonic generation microscopy to investigate individual persistent luminescent microparticles that are either embedded in glass or as prepared. Three-dimensional mapping of the second-harmonic generation from monoclinic dysprosium- and europium-doped strontium aluminates, a popular persistent luminescent material, allows us to unambiguously visualize and reveal for the first time the presence of micrometer-sized structured domains from such microparticles. The technique was found to have high potential for studying noninvasively a wide range of individual persistent luminescent entities that are embedded in a variety of glass matrices. publishedVersion

In the present work, we studied Er-doped KPO3-Ca(PO3)2 metaphosphate glass and its devitrification behavior. It is shown that two concurrent crystallization processes (surface and bulk crystallization) are observed in this glass with the precipitation of two different phases of KCa(PO3)3: the hexagonal phase is mostly formed at the surface, whereas the orthorhombic isomorph is found in the bulk. The possibility of synthetizing a transparent glass-ceramic is demonstrated. From the changes in the spectroscopic properties of the obtained glass-ceramic materials, Er3+ ions are suspected to enter into the lattice of the KCa(PO3)3 crystal. acceptedVersion

We report a study on the development of novel oxyfluoride phosphate glasses which could be used for the fabrication of transparent glass-ceramic fibers. In order to increase the thermal stability of the glass in order to draw fiber from this glass, Fe2O3 was added in the phosphate network. We first discuss the impact of the changes in the glass composition on the thermal, optical, structural and luminescence properties of the glass. Then, the influence of Fe2O3 addition on the crystallization of the glasses is assessed with the aim to define a glass composition that can be processed into transparent glass-ceramic. acceptedVersion

Phosphate glasses with the composition (90NaPO3-(10-x)Na2O-xNaF) (mol%) with x = 0 and 10 were prepared with blue persistent luminescence (PeL) using direct particles doping method. Commercial CaAl2O4:Eu2+,Nd3+ microparticles (MPs) with blue PeL were added in the glass melt at a lower temperature than the melting temperature. The PeL properties of the glasses were related to the diffusion of Al from the MPs to the glass occurring during the glass preparation, which was found to depend on the temperature at which the MPs are added in the melt and also on the time before casting the melt after adding the MPs. The glass with x = 0 can be prepared with homogeneous PeL if the MPs are added at 575 °C. This Tdoping temperature can be reduced to 550 °C by replacing Na2O by NaF in the glass.

Persistent luminescence (PeL) was obtained from glasses with the composition (75NaPO3-25CaF2) (in mol%) by adding PeL microparticles SrAl2O4:Eu2+,Dy3+ in the melts using the direct doping method. The glasses exhibit a strong PeL although they crystallize upon quenching. The crystallization was related to the poor thermal stability of the glass, and also to the extensive loss of fluorine during the glass preparation. The use of quartz crucibles and the long process time used to prepare glasses using the direct doping method are responsible for the fluorine losses.

Er3+ doped tellurite-based glasses were prepared using standard melting process and their physical, optical, thermal, optical and luminescence properties were measured and compared. We found that the addition of Na2O in the TeO2-ZnO system leads to higher emission at 1.5μm as compared to the addition of TeO2, Bi2O3, BaO, Nb2O5. We found that Bi2O3 should be used in order to increase the intensity of the upconversion under 976 nm excitation. The glasses were heat treated in order to grow crystals in these glasses. Surface crystallization occurred upon heat treatment with the precipitation of multiple crystals, the composition of which depends on the glass composition. The heat treatment was found to have no impact on the intensity of the emission at 1.5 μm. However, it increases the intensity of the red upconversion, especially for Bi2O3 containing glass.

Persistent luminescence (PeL) was obtained, from the first time to the best of our knowledge, from borosilicate bulk glasses. The glasses were prepared using direct doping method. Commercial PeL SrAl 2 O 4 :Eu 2+ ,Dy 3+ microparticles (MPs) were added in the borosilicate glass after melting. The persistent luminescence can be augmented when casting the glass 3 min after adding the MPs at 950 °C. Although the borosilicate glasses exhibit persistent luminescence, the glass melt has a corrosive behavior on the MPs leading to the diffusion of Al and Sr into the glasses.

We report our findings on the impact of the glass composition on the corrosion of microparticles occurring during the preparation of glass-ceramics using the direct doping method. Microparticles (MPs) with the composition Sr4Al14O25:Eu2+,Dy3+ with blue-green persistent luminescence were chosen as the changes in their spectroscopic properties can be related to the MPs’ corrosion. The MPs were added in phosphate-based glasses with different compositions. When using the same doping parameters, the glass system with the composition 90NaPO3-10Na2O (mol%) was found to be the least corrosive on the MPs whereas the glass system with the composition 90NaPO3-10NaF (mol%) is the most corrosive on the MPs probably due to their different viscosity at 575 °C, the temperature at which the MPs are added in the glass melts.