Nanocrystallization in Oxyfluoride Glasses Controlled by Amorphous Phase Separation

Theoretical and experimental investigation of Al3+ ion-suppressed phase-separation structures in rare-earth-doped high-phosphorus silica glasses

Rare-earth-doped silica-based composite glasses (Re-SCGs) are widely used as high-quality laser gain media in defense, aerospace, energy, power, and medical applications. The variable regional chemical environments of Re-SCGs can induce new photoluminescence properties of rare-earth ions but can cause the selective aggregation of rare-earth ions, limiting the application of Re-SCGs in the field of high-power lasers. Here, topological engineering is proposed to adjust the degree of cross-linking of phase-separation network chains in Re-SCGs. A combination of experimental and theoretical characterization techniques suggested that the selective aggregation of rare-earth ions originates from the formation of phase-separated structures in glasses. The decomposition of nanoscale phase separation structures to the sub-nanometer scale, enabled by incorporating Al3+ ions, not only maintains the high luminescence efficiency of rare earth ions but also increases light transmittance and reduces light scattering. Furthermore, our investigation encompassed the exploration of the inhibitory mechanism of Al3+ ions on phase-separation structures, as well as their influence on the spectral characteristics of Re-SCGs. This work provides a new design concept for composite glass materials doped with rare-earth ions and could broaden their application in the field of high-power lasers.

Band Gap and Defect Engineering Enhanced Scintillation from Ce3+-Doped Nanoglass Containing Mixed-Type Fluoride Nanocrystals

Much can be learned from the research and development of scintillator crystals for improving the scintillation performance of glasses. Relying on the concept of "embedding crystalline order in glass", we have demonstrated that the scintillation properties of Ce3+-doped nanoglass composites (nano-GCs) can be optimized via the synergistic effects of Gd3+-sublattice sensitization and band-gap engineering. The nano-GCs host a large volume fraction of KYxGd1-xF4 mixed-type fluoride nanocrystals (NCs) and still retain reasonably good transparency at Ce3+-emitting wavelengths. The light yield of 3455 ± 20 ph/MeV is found, which is the largest value ever reported in fluoride NC-embedded nano-GCs. A comprehensive study is given on the highly selective doping of Ce3+ in the NCs and its positive effect on the scintillation properties. The favorable influence of the Y3+/Gd3+ mixing on the suppression of defects is accounted for by density functional theory and borne out experimentally. As a proof-of-concept, X-ray imaging with a good spatial resolution (7.9 lp/mm) is demonstrated by employing Ce3+-doped nano-GCs. The superior radiation hardness, repeatability, and thermal stability of the designed scintillators bode well for their long-term practical applications.

Variable ratio blue/red upconversion in Yb3+-Tm3+ codoped fluorosilicate glasses

Simultaneous blue-red emission in a fiber pumped by a single wavelength source is perceived as a great challenge because of the large energy difference of the emitted photons. This Letter reports the dependence of the blue-to-red upconversion (UC) emission ratio in Yb³⁺-Tm³⁺ codoped fluorosilicate glasses (FSGs) under the excitation of a 980-nm laser on the host glass silica content. Photoluminescence spectra and SEM-EDS are used to clarify the UC mechanism, indicating that the probability of the cross-relaxation (CR) process ¹G₄+ ³F₂→³H₆+ ³F₄ is key to the dominance of the blue or red emissions. This research can provide a new platform for variable UC luminescence.

High resolution compact spectrometer system based on scattering and spectral reconstruction

In this Letter, we present a compact scattering spectrometer system based on fluorosilicate glass ceramics. By the algorithmic spectral calibration and reconstruction, we achieve wavelength detection with a resolution of 0.1 nm. Numerous nanocrystals embedded in the glass host in the glass ceramics result in a significant natural multilayer scattering medium, which can provide a 60% scattering efficiency for incident light while increasing the optical path of incident light transmitting in the medium. The glass ceramics scattering medium with a rather compact physical size is integrated with a low-cost camera to compose an optical spectral system, which has potential application in lab-on-a-chip optical spectroscopy.

Ln2Te6O15 (Ln = La, Gd, and Eu) "Anti-Glass" Phase-Assisted Lanthanum-Tellurite Transparent Glass-Ceramics: Eu3+ Emission and Local Site Symmetry Analysis

The presence of lanthanide-tellurite "anti-glass" nanocrystalline phases not only affects the transparency in glass-ceramics (GCs) but also influences the emission of a dopant ion. Therefore, a methodical understanding of the crystal growth mechanism and local site symmetry of doped luminescent ions when embedded into the precipitated "anti-glass" phase is crucial, which unfolds the practical applications of GCs. Here, we examined the Ln₂Te₆O₁₅ "anti-glass" nanocrystalline phase growth mechanism and local site symmetry of Eu³⁺ ions in transparent GCs produced from 80TeO₂-10TiO₂-(5 - x)La₂O₃-5Gd₂O₃-xEu₂O₃ glasses, where x = 0, 1, 2. A crystallization kinetics study identifies a unique crystal growth mechanism via a constrained nucleation rate. The extent of "anti-glass" phase precipitation and its growth in GCs with respect to heat-treatment duration is demonstrated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis. Qualitative analysis of XRD confirms the precipitation of both La₂Te₆O₁₅ and Gd₂Te₆O₁₅ nanocrystalline phases. Rietveld refinement of powder X-ray diffraction patterns reveals that Eu³⁺ ions occupy "Gd" sites in Gd₂Te₆O₁₅ over "La" sites in La₂Te₆O₁₅. Raman spectroscopy reveals the conversion of TeO₃ units to TeO₄ units with Eu₂O₃ addition. This confirms the polymerizing role of Eu₂O₃ and consequently high crystallization tenacity with increasing Eu₂O₃ concentration. The measured Eu³⁺ ion photoluminescence spectra revealed its local site symmetry. Moreover, the present GCs showed adequate thermal cycling stability (∼50% at 423 K) with the highest activation energy of around 0.3 eV and further suggested that the present transparent GCs would be a potential candidate for the fabrication of red-light-emitting diodes (LEDs) or red component phosphor in W-LEDs.

Phase transitions affected by natural and forceful molecular interconversion

If a binary liquid mixture, composed of two alternative species with equal amounts, is quenched from a high temperature to a low temperature, below the critical point of demixing, then the mixture will phase separate through a process known as spinodal decomposition. However, if the two alternative species are allowed to interconvert, either naturally (e.g., the equilibrium interconversion of enantiomers) or forcefully (e.g., via an external source of energy or matter), then the process of phase separation may drastically change. In this case, depending on the nature of interconversion, two phenomena could be observed: either phase amplification, the growth of one phase at the expense of another stable phase, or microphase separation, the formation of nongrowing (steady-state) microphase domains. In this work, we phenomenologically generalize the Cahn–Hilliard theory of spinodal decomposition to include the molecular interconversion of species and describe the physical properties of systems undergoing either phase amplification or microphase separation. We apply the developed phenomenology to accurately describe the simulation results of three atomistic models that demonstrate phase amplification and/or microphase separation. We also discuss the application of our approach to phase transitions in polyamorphic liquids. Finally, we describe the effects of fluctuations of the order parameter in the critical region on phase amplification and microphase separation.

Nano-imaging confirms improved apatite precipitation for high phosphate/silicate ratio bioactive glasses

Bioactive glasses convert to a biomimetic apatite when in contact with physiological solutions; however, the number and type of phases precipitating depends on glass composition and reactivity. This process is typically followed by X-ray diffraction and infrared spectroscopy. Here, we visualise surface mineralisation in a series of sodium-free bioactive glasses, using transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy (EDXS) and X-ray nano-computed tomography (nano-CT). In the glasses, the phosphate content was increased while adding stoichiometric amounts of calcium to maintain phosphate in an orthophosphate environment in the glass. Calcium fluoride was added to keep the melting temperature low. TEM brought to light the presence of phosphate clustering and nearly crystalline calcium fluoride environments in the glasses. A combination of analytical methods, including solid-state NMR, shows how with increasing phosphate content in the glass, precipitation of calcium fluoride during immersion is superseded by fluorapatite precipitation. Nano-CT gives insight into bioactive glass particle morphology after immersion, while TEM illustrates how compositional changes in the glass affect microstructure at a sub-micron to nanometre-level.

High-efficiency luminescence in optical glass via the controllable crystallization of KYb3F10 nanocrystals depending on the dopants

A transparent glass ceramic (GC) is designed via the controllable precipitation of KYb₃F₁₀ nanocrystals. It is shown that the crystallization in GC deeply depends on the doping of Yb³⁺. Yb³⁺ ions are spontaneously distributed in the fluoride crystal environments without the ionic substitution process of traditional GC. As a result, high-efficiency upconversion (UC) luminescence is achieved in GC. The UC quantum yield value of the Yb³⁺-Er³⁺-codoped GC is as high as 1.44±0.02%, which is more than 20 times higher than the traditional GC containing NaYF₄ crystals. The designed GC offers opportunities for the promising development of active optical devices, and the crystallization strategy of this GC provides a powerful solution to conquer the bottleneck in luminescence efficiency of the traditional GCs.

Deep UV random lasing from NaGdF4:Yb3+,Tm3+ upconversion nanocrystals in amorphous borosilicate glass

The realization of lanthanide-doped upconversion nanocrystals embedded in a robust and transparent solid medium is highly desired to achieve deep UV (<300nm) lasing. Here, we fabricate NaGdF₄:Yb³⁺,Tm³⁺ upconversion nanocrystals inside amorphous borosilicate glass to support ∼290nm random lasing emission under 980 nm excitation. We found that with careful control of the growth process, which is the key to achieve high-crystallinity nanocrystals, the nanocrystals can suppress defect-related quenching and enhance ¹I₆→³H₆(⁶I_J→⁸S_7/2) transition of Tm³⁺ (Gd³⁺) ions under five-photon absorption excitation so that high optical gain (>45cm^-1) at ∼290nm can be obtained.

High-security-level multi-dimensional optical storage medium: nanostructured glass embedded with LiGa5O8: Mn2+ with photostimulated luminescence

The launch of the big data era puts forward challenges for information preservation technology, both in storage capacity and security. Herein, a brand new optical storage medium, transparent glass ceramic (TGC) embedded with photostimulated LiGa₅O₈: Mn²⁺ nanocrystals, capable of achieving bit-by-bit optical data write-in and read-out in a photon trapping/detrapping mode, is developed. The highly ordered nanostructure enables light-matter interaction with high encoding/decoding resolution and low bit error rate. Importantly, going beyond traditional 2D optical storage, the high transparency of the studied bulk medium makes 3D volumetric optical data storage (ODS) possible, which brings about the merits of expanded storage capacity and improved information security. Demonstration application confirmed the erasable-rewritable 3D storage of binary data and display items in TGC with intensity/wavelength multiplexing. The present work highlights a great leap in photostimulated material for ODS application and hopefully stimulates the development of new multi-dimensional ODS media.

Upconversion luminescence modulated by alkali metal (Li, Na, and K) induced crystallization in Er3+/Yb3+ co-doped β-PbF2 oxyfluoride glass ceramics

Upconversion luminescence of Er³⁺/Yb³⁺ co-doped β-PbF₂ oxyfluoride glass ceramics modulated by alkali metals (Li, Na, and K).

CsRe2F7@glass nanocomposites with efficient up-/down-conversion luminescence: from in situ nanocrystallization synthesis to multi-functional applications

Recently, lanthanide-doped luminescent materials have been widely studied and most investigations have been limited to rare-earth-containing fluorides formed with lighter alkali metals (Li, Na and K). Hence, it is important to understand the luminescence properties of cesium rare-earth fluorides. Herein, a novel type of multi-functional luminescent material, hexagonal β-CsRe2F7 (Re = La-Lu, Y, Sc) nanocrystals, is successfully prepared via in situ crystallization inside glass. Specifically, Yb/Er:β-CsLu2F7@glass exhibits a much higher upconversion quantum yield than Yb/Er:β-NaYF4@glass (about 6 times), which is believed to be one of the most efficient upconversion materials so far. Impressively, Er:CsYb2F7@glass shows a significant photothermal effect, which can produce variable upconversion emission colors induced by an incident 980 nm laser diode, enabling it to find practical application in novel/high-precision anti-counterfeiting. In addition, Ce:CsLu2F7@glass with a maximal photoluminescence quantum yield reaching 67% can yield intense X-ray excitable radioluminescence, which is even higher than that of a commercial Bi4Ge3O12 scintillator. Benefitting from the effective protection of robust oxide glass, lanthanide-doped CsRe2F7 nanocrystals show long-term stability in harsh environments, retaining near 100% luminescence after directly immersing them in water/oil for 30 days. It is expected that the present nanocomposites have potential applications in the fields of high-end upconversion anti-counterfeiting and high-energy radiation detection.

Simultaneous Tailoring of Dual-Phase Fluoride Precipitation and Dopant Distribution in Glass to Control Upconverting Luminescence

In situ glass crystallization is an effective strategy to integrate lanthanide-doped upconversion nanocrystals into amorphous glass, leading to new hybrid materials and offering an unexploited way to study light-particle interactions. However, the precipitation of Sc³⁺-based nanocrystals from glass is rarely reported and the incorporation of lanthanide activators into the Sc³⁺-based crystalline lattice is formidably difficult owing to their large radius mismatch. Herein, it is demonstrated that lanthanide dopants with smaller ionic radii can act as nucleating agents to promote the nucleation/growth of KSc₂F₇ nanocrystals in oxyfluoride aluminosilicate glass. A series of structural and spectroscopic characterizations indicate that Ln-dopant-induced K/Sc/Ln/F amorphous phase separation from glass is an essential prerequisite for the precipitation of KSc₂F₇ and the partition of Ln dopants into the KSc₂F₇ lattice by substituting Sc³⁺ ions. Importantly, modifying the Ln-to-Sc ratio in glass enables to control competitive crystallization of KSc₂F₇ and Ln-based (KYb₂F₇, KLu₂F₇, and KYF₄) nanocrystals and produce dual-phase fluoride-embedded nanocomposites with distinct crystal fields. Consequently, tunable multicolor upconversion luminescence can be achieved through diversified regulatory approaches, such as adjustment of the dual-phase ratio, selective separation of Ln³⁺ dopants, and alteration of incident pumping laser. As a proof-of-concept experiment, the application of dual-phase glass as a color converter in 980 nm laser-driven upconverting lighting is demonstrated.

Ultrabright single-band red upconversion luminescence in highly transparent fluorosilicate glass ceramics containing KMnF3 perovskite nanocrystals

With a specially designed composition, highly transparent Yb³⁺/Er³⁺-doped fluorosilicate glass ceramic (GC) containing KMnF₃ perovskite nanocrystals (NCs) is obtained for the first time. The rare-earth ions are preferentially accumulated in regions embedded with KMnF₃ NCs; as a result, a remarkably enhanced (by an order of magnitude) single-band red upconversion luminescence (UCL) is achieved. Absolute quantum efficiency of the red UCL, which cannot be measured in previous GCs owing to insufficiency, reaches as high as 0.10%±0.02% in the GC sample reported in this Letter. This value is even higher than that of the well-known multiband emitting β-NaYF₄:Er³⁺/Yb³⁺ NCs and widely recognized GCs containing NaYF₄:Yb³⁺/Er³⁺NCs.

Upconversion of transparent glass ceramics containing β-NaYF4:Yb3+, Er3+ nanocrystals for optical thermometry

β-NaYF₄ nanocrystal embedded glass ceramics were fabricated by a melt-quenching method with subsequent heat-treatment. Structural characterizations and spectrographic techniques were performed to verify the successful precipitation of β-NaYF₄ nanocrystals and partition of dopants. Upon excitation of 980 nm, bright green upconversion emission could be achieved in Yb³⁺, Er³⁺ codoped β-NaYF₄ nanocrystal embedded glass ceramics. Furthermore, the temperature-dependent upconversion behaviour based on thermally coupled energy levels was also examined in the range of 300–773 K with the maximum relative sensitivity of 1.24% K⁻¹ at 300 K. Accordingly, it has been proved to be a promising candidate for application in optical thermometry.

β-NaYF₄:Yb³⁺, Er³⁺ nanocrystals embedded glass ceramics have been fabricated and demonstrates excellent performance for optical thermometry.

Broadband multicolor upconversion from Yb3+-Mn2+ codoped fluorosilicate glasses and transparent glass ceramics

In contrast to well-known upconversion (UC) emission from Yb³⁺-Mn²⁺-codoped crystal, a room-temperature intense broadband UC phenomenon was first observed in both Yb³⁺-Mn²⁺-codoped fluorosilicate glasses and transparent glass ceramics under 980 nm pumping. The obtained photoluminescence ranged from yellow to white to blue. We attributed this effect to the cooperative UC of Yb³⁺ and to the formation of Yb³⁺-Mn²⁺ pairs. After heat treatment, KZnF₃ nanocrystals appeared in the glass matrix, as identified by x-ray diffraction and transmission electron microscopy, and emission intensity increased 45 times. We believe that Yb³⁺-Mn²⁺-codoped glasses and glass ceramics show great potential as materials for multicolor displays.

Transparent Na5Gd9F32:Er3+ glass-ceramics: enhanced up-conversion luminescence and applications in optical temperature sensors

New rare earth ion-doped nanocomposite materials, Na₅Gd₉F₃₂:Er³⁺ glass-ceramics, were fabricated. Excited by 980 nm, the glass-ceramics present enhanced up-conversion emission and show good optical temperature sensing property.

Retracted Article: Self-limited growth of Pr3+-doped LaF3 nanocrystals in oxyfluoride glass and glass-ceramics

Droplets of Pr³⁺-doped LaF₃ nanocrystals in oxyfluoride glass and glass-ceramics self-limitedly grow through phase separation. The Al concentrated middle layer is sandwiched between La, F and Pr enriched inner core and Si augmented exterior shell.

Phase structure control and optical spectroscopy of rare-earth activated GdF3 nanocrystal embedded glass ceramics via alkaline-earth/alkali-metal doping

Alkaline-earth/alkali-metal dopant-induced hexagonal and orthorhombic GdF₃ nanocrystal embedded glass ceramics were fabricated via glass crystallization.

Broadband near-IR emission from cubic perovskite KZnF(3):Ni(2+) nanocrystals embedded glass-ceramics

Transparent KF-ZnF(2)-SiO(2) glass-ceramics were prepared with the precipitation of KZnF(3)Ni(2+) nanocrystals. During excitation with a wavelength of 405 nm at room temperature, a broadband near-IR emission centered at 1695 nm with the FWHM of more than 350 nm was observed, which is originated from the T(2g)3(F3)→A(2g)3(F3) transition of octahedral Ni(2+) incorporated in the KZnF(3) crystalline phase. In comparison to oxide glass-ceramics, a redshift of the luminescence is observed, which is due to the low crystal field of these octahedral Ni(2+). The shift and extension of near-IR emission in the KZnF(3):Ni(2+) nanocrystals embedded in a glassy matrix do not only complete the broadband emission in the whole near-IR region for the Ni(2+) ions-based photonics, but also open an easy way to approach the broadband optical amplifier and tunable lasers operating in the wavelength region near 1800 nm, which was up to now achieved by codoping of several types of active ions.