Luminescent ion-doped transparent glass ceramics for mid-infrared light sources [invited]

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.

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.

Se-H-free As2Se3 fiber and its spectral applications in the mid-infrared

The complete removal of the impurities like Se-H in Se-based chalcogenide glasses has been challenging in the development of highly transparent chalcogenide glass fiber. In this paper, several purification methods, including dynamic distillation, static distillation, and combined distillation method, were adopted with an aim of purifying arsenic selenide glass with ultra-low content of the impurities. The experimental results demonstrated that the Se-H can be completely eliminated in the arsenic selenide glass host and fiber without the introduction of any chloride. We further explored the applications of such low loss and Se-H-free chalcogenide glass fiber in the mid-infrared. It was found that, using such a Se-H free fiber, a flattened supercontinuum spectrum above the -30 dB level from 1.2 to 13 µm was generated from the Se-H free fiber with a 5.5 µm laser pumping. The sensitivity was found to be improved 5.1 times for CO₂ gas in the 3 to 6 µm wavelength range.

Crystallization Mechanism and Optical Properties of Antimony-Germanate-Silicate Glass-Ceramic Doped with Europium Ions

Glass-ceramic is semi-novel material with many applications, but it is still problematic in obtaining fibers. This paper aims to develop a new glass-ceramic material that is a compromise between crystallization, thermal stability, and optical properties required for optical fiber technology. This compromise is made possible by an alternative method with a controlled crystallization process and a suitable choice of the chemical composition of the core material. In this way, the annealing process is eliminated, and the core material adopts a glass-ceramic character with high transparency directly in the drawing process. In the experiment, low phonon antimony-germanate-silicate glass (SGS) doped with Eu³⁺ ions and different concentrations of P₂O₅ were fabricated. The glass material crystallized during the cooling process under conditions similar to the drawing processes'. Thermal stability (DSC), X-ray photo analysis (XRD), and spectroscopic were measured. Eu³⁺ ions were used as spectral probes to determine the effect of P₂O₅ on the asymmetry ratio for the selected transitions (⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂). From the measurements, it was observed that the material produced exhibited amorphous or glass-ceramic properties, strongly dependent on the nucleator concentration. In addition, the conducted study confirmed that europium ions co-form the EuPO₄ structure during the cooling process from 730 °C to room temperature. Moreover, the asymmetry ratio was changed from over 4 to under 1. The result obtained confirms that the developed material has properties typical of transparent glass-ceramic while maintaining high thermal stability, which will enable the fabrication of fibers with the glass-ceramic core.

Highly stable CsPbBr3 perovskite quantum dot-doped tellurite glass nanocomposite scintillator

All-inorganic cesium lead halide perovskite quantum dots (PQDs) appear to be promising scintillators for radiation detection; however, they are suffering from poor stabilities against light, heat, and moisture. Here a strategy of using AgCl as the nucleating agent is developed to facilitate growth of CsPbBr₃ PQDs in chemically inert tellurite glasses via controlled crystallization. The PQDs are uniformly dispersed and well protected in the dense glass matrix without aggregation. The nanocomposites thus obtained are featured by excellent optical transparency owing to the unique character of tellurite glass having a refractive index comparable to that of the CsPbBr₃ crystal. The X-ray excited radioluminescence properties are comprehensively studied. The results show that CsPbBr₃ PQD-doped tellurite glasses are highly stable against continuous X-ray irradiation and repeated heat-cooling cycles (from room temperature up to 573 K) without sacrificing their scintillation properties, thus appearing to be a potential scintillator for long-term practical applications.

Efficient white upconversion luminescence in Yb3+/Eu3+ doubly-doped transparent glass ceramic

Efficient white upconversion (UC) luminescence is obtained in Yb³⁺/Eu³⁺ doubly-doped optical glass ceramic (GC) for the first time. KYb₃F₁₀ nanocrystals are controllably precipitated from the amorphous networks via the inducing of Yb³⁺. Yb³⁺ ions are spontaneously confined within the compact fluoride crystal structures to produce efficient blue UC emissions of Yb³⁺-Yb³⁺ pairs. Eu³⁺ ions are easily incorporated into the KYb₃F₁₀ crystal lattices. Owing to the extremely short interionic distance in the crystal structures, intense green UC emissions apart from the red emissions of Eu³⁺ are observed, which are not obtained by the traditional Yb³⁺/Eu³⁺ doubly-doped GCs. As a result, white UC emissions are synthesized based on the three-primary-color principle and the emission intensities of GCs are dramatically enhanced as compared to glass. The designed GCs provide novel optical gain materials for the promising applications in three-dimensional display, solid-state lighting and tunable fiber lasers.

Thermal Evolutions to Glass-Ceramics Bearing Calcium Tungstate Crystals in Borate Glasses Doped with Photoluminescent Eu3+ Ions

Thermal evolutions of calcium-tungstate-borate glasses were investigated for the development of luminescent glass-ceramics by using Eu³⁺ dopant in a borate glass matrix with calcium tungstate, which was expected to have a combined character of glass and ceramics. This study revealed that single-phase precipitation of CaWO₄ crystals in borate glass matrix was possible by heat-treatment at a temperature higher than glass transition temperature T_g for (100-x) (33CaO-67B₂O₃)-xCa₃WO₆ (x = 8-15 mol%). Additionally, the crystallization of CaWO₄ was found by Raman spectroscopy due to the formation of W=O double bondings of WO₄ tetrahedra in the pristine glass despite starting with the higher calcium content of Ca₃WO₆. Eu³⁺ ions were excluded from the CaWO₄ crystals and positioned in the borate glass phase as a stable site for them, which provided local environments in higher symmetry around Eu³⁺ ions.

Fiber-based sources of coherent MIR radiation: key advances and future prospects (invited)

The mid-infrared (MIR) represents a large portion of the electromagnetic spectrum that is progressively being exploited for an enormous number of applications. Thermal imaging cameras, dental and skin resurfacing lasers, and narcotics detectors at airports are all mainstream examples involving the MIR, but potential applications of MIR technologies are much larger. Accessing the unique opportunities afforded by the MIR is critically dependent on the specific characteristics of MIR emitting sources that become available. In this review, we survey an important enabling technology to the opening up of MIR science and applications, namely that driven by fiber-based sources of coherent MIR radiation. In this review paper, we describe many of the key advances in the innovation and development of such sources over the past few decades and discuss many of the underlying science and technology issues that have resulted in specific recent source achievements, especially in light of new applications enabled by these new source capabilities. We also discuss a few specific anticipated future needs and some potentially disruptive approaches to future MIR fiber source development.