Coloration and Nonlinear Optical Properties of ZnTe Quantum Dots in ZnO–TeO2–P2O5 Glasses

ZnO–TeO₂–P₂O₅ glasses were prepared by melt‐quenching method. The color of the glass samples changed from colorless to pale red and dark red with increasing TeO₂ content. Coloration mechanism and nonlinear optical properties of ZnO–TeO₂–P₂O₅ glasses have been investigated. Raman spectra and transmission electron microscope measurements indicated the precipitation of ZnTe quantum dots in the glasses and ZnTe quantum dots are the origin of coloration. Z‐scan technique was used to examine the nonlinear optical properties of the glasses. The glass sample with 30 mol% TeO₂ exhibits large third‐order nonlinear optical susceptibility of 10^?11 esu.     

Glass-forming region and enhanced Bi NIR emission in sodium tantalum silicate laser glass

Bismuth (Bi)-doped glasses and fibers are of current interest as promising active media for new fiber lasers and amplifiers due to their 800-1700 nm near-infrared (NIR) emission. However, the optically active Bi centers in silica are easily volatilized during high-temperature fiber drawing, which results in low Bi doping concentration and low gain NIR luminescence. Here, we explored the glass-forming region in a model glass system of sodium tantalum silicate (Na₂O-Ta₂O₅-SiO₂) glass and attained suitable glass host for enhancing Bi NIR emission, right followed by detailed analysis on optical and structural characterization. Glass-forming region roughly lies in where Ta₂O₅ ≤ 30 mol%, SiO₂ ≥ 40 mol%, and Na₂O ≤ 40 mol%. Not only is glass-forming ability improved but also Bi NIR emission is enhanced (~60 times) by the introduction of Ta into glass network. Dissociated Na cations are restricted beside Ta, the high-field-strength element, so that the negative impacts of Na cations on glass formation and Bi NIR emission are weakened, which is responsible for the highly enhanced Bi NIR emission. This work helps us understand the glass-forming of tantalum silicate glass systems and luminescent behaviors of Bi. Hopefully, it could contribute to designing the Bi-doped laser glasses and high gain fibers with stable luminescent properties in future.     

Effect of the Glass Structure on Emission of Rare‐Earth‐Doped Borate Glasses

A series of glasses composed of xB₂O₃–8Al₂O₃‐(90?x)Na₂O–R₂O₃ (x = 65, 70, 75, 80, 85; R = Dy³⁺, Tb³⁺, Sm³⁺) were prepared through melt‐quenching. Structural evolution was induced by varying the glass composition. Increasing the glass network former B₂O₃ enhanced the luminescence of rare‐earth ions, as observed in the emission spectra. The mechanism of the glass structural evolution was investigated by the NMR spectra analysis. The dispersant effect of the glass structure was believed to promote the better distribution of the rare‐earth ions in the matrix and reduced the concentration quenching between them. The relationship between the glass structure and its optical properties was established.     

Improving luminescence behavior and glass stability of tellurium-doped germanate glasses by modifying network topology

Broadband near-infrared (NIR) luminescent materials are of great interest for their potential application in optical communication, remote sensing, imaging, and homeland security. Tellurium (Te) doped glasses were recently recognized as such a promising candidate due to their broadband NIR emission (700–1700 nm). However, the achievement of Te-doped glasses with high luminescence efficiency and glass stability (GS) remains a daunting challenge. Here, the luminescence behavior and GS of Te-doped germanate glasses are manipulated by tailoring the glass network topology. Te NIR luminescence is enhanced by tailoring topological cages in germanate glass network structure through varying glass network modifiers. Meanwhile, the GS of potassium germanate glass is significantly enhanced due to increased network connectivity caused by the co-introduction of alkaline earth oxides. Finally, NIR luminescence intensity of the glass was further enhanced by optimizing the doping concentration of TeO₂. The findings here could contribute to designing Te-activated glasses with improved performance for application in optical amplifiers and tunable fiber lasers.     

Effect of the Eu3+ Addition on Photoluminescence and Microstructure of ZnO–CdO–TeO2 Glasses

In this work, the role of europium doping of glasses formulated in the ternary system ZnO–CdO–TeO₂ is described. The Eu‐doped oxide glasses were prepared by the conventional melt‐quenching method and by using three different compositions. Structural studies reveal that there exists a good affinity between Cd and some rare earth (RE) ions to form the crystalline phase. The X‐ray diffraction (XRD) diagrams display that the structure of these glasses is amorphous and with the increase in CdO content and the compatibility of Eu³⁺, there is a tendency to form nanocrystals of CdTe₂O₅. The scanning electron microscopic (SEM) observation of their microstructure confirms the presence of phase separation. Differential thermal analysis (DTA) of these glasses showed small exothermic peaks noted around 450°C for the V2 glass and 480°C for V1 and V3 glasses, which could be attributed to the formation of these crystals. The infrared spectra showed a main absorption band around 800–600 cm^?1 corresponding to the Te–O stretching mode in TeO₄ and TeO₃ groups. By optical absorption (OA), the band gap (E_g) for each glass was determined; these values were 3.27, 3.14, and 3.3 eV for the V1–V3 glasses, respectively. Furthermore, the presence of Eu³⁺ was detected in the 370–470 nm short‐range wavelengths. The photoluminescence (PL) experiments of the glasses showed light emission due to the following transitions: ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂, ⁵D₀ → ⁷F₃, and ⁵D₀ → ⁷F₄.     

Er3+ ‐Doped Y2O3 Nanophosphors for Near‐Infrared Fluorescence Bioimaging Applications

Rare‐earth‐doped ceramic nanophosphor (RED‐CNP) materials are promising near‐infrared (NIR) fluorescence bioimaging (FBI) agents that can overcome problems of currently used organic dyes including photobleaching, phototoxicity, and light scattering. Here, we report a NIR–NIR bioimaging system by using NIR emission at 1550 nm under 980 nm excitation which can allow a deeper penetration depth into biological tissues than ultraviolet or visible light excitation. In this study, erbium‐doped yttrium oxide nanoparticles (Er³⁺:Y₂O₃) with an average particle size of 100 and 500 nm were synthesized by surfactant‐assisted homogeneous precipitation method. NIR emission properties of Er³⁺:Y₂O₃ were investigated under 980 nm excitation. The surface of Er³⁺:Y₂O₃ was electrostatically PEGylated using poly (ethylene glycol)‐b‐poly(acrylic acid) (PEG‐b‐PAAc) block copolymer to improve the chemical durability and dispersion stability of Er³⁺:Y₂O₃ under physiological conditions. In vitro cytotoxic effects of bare and PEG‐b‐PAAc‐modified Er³⁺:Y₂O₃ were investigated by incubation with mouse macrophage cells (J774). Microscopic and macroscopic FBI were demonstrated in vivo by injection of bare or PEG‐b‐PAAc‐modified Er³⁺:Y₂O₃ into C57BL/6 mice. The NIR fluorescence images showed that PEG‐b‐PAAc modification significantly reduced the agglomeration of Er³⁺:Y₂O₃ in mice and enhanced the distribution of Er³⁺:Y₂O₃.     

Optical Investigation of Ce3+‐Activated Borogermanate Glass Induced by Substitution of BaF2 for BaO

Transparent and colorless CeO₂‐activated borogermanate glasses, with the nominal molar composition of 25B₂O₃–40GeO₂–14Gd₂O₃–1CeO₂–(20?x) BaO–xBaF₂ (x = 0, 2.5, 5, 10, 15 and 20), were synthesized by a melt‐quenching method in air. Their optical investigation on the transmittance, photoluminescence (excitation and emission spectra), the luminescence decay curves, as well as the temperature‐dependent Ce³⁺ emission are studied systematically with the gradual substitution of BaF₂ for BaO. The room‐temperature photoluminescence results reveal that the emission intensity can be improved by about 2.5 times with the full substitution of BaF₂ for BaO. The blue shift of the cut‐off edge, excitation and emission spectra of Ce³⁺‐activated borogermanate glass, and the emission intensity of Ce³⁺ ions as a function of temperature range in 80–500 K are also discussed.     

Structural and emission properties of Eu3+‐doped alkaline earth zinc‐phosphate glasses for white LED applications

Quaternary alkaline earth zinc‐phosphate glasses in molar composition (40 ? x)ZnO – 35P₂O₅ – 20RO – 5TiO₂ – xEu₂O₃ (where x=1 and R=Mg, Ca, Sr, and Ba) were prepared by melt quenching technique. These glasses were studied with respect to their thermal, structural, and photoluminescent properties. The maximum value of the glass transition temperature (T_g) was observed for BaO network modifier mixed glass and minimum was observed for MgO network modifier glass. All the glasses were found to be amorphous in nature. The FT‐IR suggested the glasses to be in pyrophosphate structure, which matches with the theoretical estimation of O/P atomic ratio and the maximum depolymerization was observed for glass mixed with BaO network modifier. The intense emission peak was observed at 613 nm (⁵D₀→⁷F₂) under excitation of 392 nm, which matches well with excitation of commercial n‐UV LED chips. The highest emission intensity and quantum efficiency was observed for the glass mixed with BaO network modifier. Based on these results, another set of glass samples was prepared with molar composition (40 ? x)ZnO – 35P₂O₅ – 20BaO – 5TiO₂ – xEu₂O₃ (x=3, 5, 7, and 9) to investigate the optimized emission intensity in these glasses. The glasses exhibited crystalline features along with amorphous nature and a drastic variation in asymmetric ratio at higher concentration (7 and 9 mol%) of Eu₂O₃. The color of emission also shifted from red to reddish orange with increase in the concentration of Eu₂O₃. These glasses are potential candidates to use as a red photoluminsecent component in the field of solid‐state lighting devices.     

Controllable ultra-broadband visible and near-infrared photoemissions in Bi-doped germanium-borate glasses

The design of functional materials with tunable broadband luminescence performance is still of great interest in the fields of lighting, solar cells, tunable lasers, and optical amplifiers. Here, via a melt-quenching method, a series of bismuth (Bi)-doped germanium-borate glasses with composition of 40GeO₂–25B₂O₃–25Gd₂O₃–10La₂O₃–xBi₂O₃ have been prepared, in which multiple Bi active centers can be stabilized simultaneously. Dual-modulating modes of visible (380-750 nm) and near-infrared (NIR) (1000-1600 nm) broadband photoemissions were effectively controlled under flexible excitation scheme. Photoluminescence (PL) spectra at low temperature 10-298 K were appropriately employed to interpret such an unusual wide visible emission band. To further illustrate the origin of NIR component, transmission electron microscopy (TEM) measurement was carried out. It is demonstrated experimentally that the visible emission mainly originates from the collective contribution of the ³P₁/³P₀¹S₀ transitions of Bi³⁺, while the broadband NIR luminescence should be related to the formation of low valent Bi⁺ and (or) Bi⁰ centers. This work may help to enhance the knowledge of the complex luminescence mechanism for the Bi species and it also enables such transparent glass materials to be a promising candidate for the multifunctional tunable light source.     

Strong Influences of Melting Time and Tm3+ Concentration on Blue Up-Conversion Photoluminescence for Tm3+/Yb3+ Co-Doped TeO2–TlO0.5–ZnO Glass

In this study, by a conventional melt quenching method, we synthesized novel up-conversion phosphors of 60TeO₂–30TlO_0.5–(9−x)ZnO–xTm₂O₃–1Yb₂O₃ (x = 0.1–0.5) glasses, whose system was recently developed in our collaborative group, and their blue up-conversion photoluminescence (UCPL) of Tm³⁺ ions via three-step energy transfer from near-infrared (NIR) sensitizer of Yb³⁺ ions was observed. In particular, the substantial rate of the energy transfer <γ_d5> in the third step from Yb³⁺ to Tm³⁺ under excitation at 975 nm, which determined the final blue UCPL intensity, was estimated as a function of the rare-earth concentration. With an aid of analytical methods of PL lifetime and Judd–Ofelt theory, it was revealed that the highest energy transfer rate <γ_d5> was achieved to be 2.07 × 10⁻¹⁷ cm³/s for x = 0.2, and further increasing Tm₂O₃ content x in the fixed Yb₂O₃ resulted in the decrease in the energy transfer rate <γ_d5>. One of the plausible causes was concentration quenching of Yb³⁺ ions. The other was back-transfer from Tm³⁺ to Yb³⁺ ions. The influence of the condition of glass synthesis and the melting time on <γ_d5> was also discussed.     

Glass Formation and Characterization Studies in the TeO2–WO3–Na2O System

Glass formation behavior of the TeO₂–WO₃–Na₂O system was studied by using conventional melt‐quenching technique. A wide glass formation range was determined for the first time in the literature and thermal, physical, and structural characterization of sodium‐tungsten‐tellurite glasses were realized using differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) spectroscopy techniques. Glass transition (T_g) and crystallization (T_c/T_p) temperatures, glass stability (?T), density (ρ), molar volume (V_M), oxygen molar volume (V_O), and oxygen packing density (OPD) values and structural transformations in the glass network were investigated according to the equimolar substitution of TeO₂ by Na₂O+WO₃ and changing Na₂O or WO₃ at constant TeO₂.     

Broadband Near‐Infrared Down‐Shifting by Yb–O Charge‐Transfer Band in Yb3+ Singly Doped Tellurite Glasses

Yb³⁺ singly doped tellurite as‐prepared glasses and glass ceramics were synthesized by high‐temperature melt‐quenching method. The excitation and emission spectra have shown that there is an efficient near‐infrared (NIR) down‐shifting due to the sensitization of a novel Yb³⁺–O^2? charge‐transfer (CT) band. The CT band in the present host is located at around 320 nm at room temperature, which is much lower than that in other oxide hosts reported before. The possible energy‐transfer mechanism from the Yb³⁺–O^2? CT band to the ²F_5/2 multiplet of Yb³⁺ ions is discussed in detail. The concentration quenching is not observed even when the Yb³⁺‐doped concentration is increased up to 40 mol%. The excitation of this strong broad CT band causes intense NIR emission of Yb³⁺:²F_5/2→²F_7/2 from 920 to 1120 nm, making the tellurite glasses suitable for efficient photovoltaic (PV) application as a spectral conversion material for the crystalline Si (c‐Si) solar cells.     

Predictable tendency of Bi NIR emission in Bi‐doped magnesium aluminosilicate laser glasses

Because of superbroad luminescence in the range of near infrared (NIR), Bi‐doped glasses and fibers have received more attentions recently for the applications in super broadband optical fiber amplifiers or new wavelength lasers. As the luminescence comes from the transitions between naked 6p orbitals of bismuth, it is very susceptible to slight changes of local field around Bi. Therefore, it is always very challenging to predict NIR emission of bismuth in advance. Here, we found bismuth NIR emission shows predictable tendency in ternary glass system of MgO–Al₂O₃–SiO₂. The emission peak shifts red along the content of magnesium upon the excitation of 484 nm, which follows a single exponential growth equation. In the meantime, the full width at half maximum (FWHM) is broadened while the lifetime keeps decreasing. Glass structure analysis on basis of FTIR, ²⁷Al NMR, ²⁹Si NMR spectra reveals that these changes correlate to integrity of glass network, the increased disorder of local field around bismuth and the enhanced interaction between bismuth and host, which are perhaps due to the linear increase of nonbridging oxygen, and the enhanced Si–O asymmetric stretching vibrations along with magnesium, respectively. Electron probe microanalysis shows good homogeneity of Si, Al, Mg, Bi, and O distribution within the samples, and yoyo experiments of heating and cooling between 30°C and 300°C reveal the good resistance of such doped glasses to thermal degradation. This makes the glasses promising in applications of fiber devices even under extreme condition such as at higher temperature. The finding in this work should be helpful for the design of Bi‐doped laser glasses in future.     

Second harmonic generation in germanotellurite bulk glass‐ceramics

In this study, we have investigated the use of silver cation as nucleating agent in germanotellurite glass matrix of compositions (100?x) [70TeO₂–10GeO₂–10Nb₂O₅–10K₂O]–xAg₂O (x=0‐6 mol%), in order to promote bulk crystallization. Density measurements, differential scanning calorimetry, X‐ray diffraction, UV‐Vis, and Raman spectroscopies have been performed to study the crystallization process. We have observed bulk crystallization of a unique noncentrosymmetric phase, K[Nb_1/3Te_2/3]₂O_4.8, which has been investigated for its second‐order optical activity. Transparent to translucent glass‐ceramics have been successfully tailored under thermal treatment and second harmonic generation signals were recorded on the glass‐ceramic samples as a function of their synthesis procedure. It is suggested that the second‐order optical properties observed are strongly related to the organization of crystallites within phase‐separated domains.     

Tunable luminescence from bismuth‐doped phosphate laser glass by engineering photonic glass structure

Because of ultra‐broadband near‐infrared (NIR) emission bismuth‐activated glasses and fibers offer a new promising platform for novel photonic devices such as new type of optical amplifiers and broadly tunable fiber lasers. Yet, challenge remains to manipulate the NIR emission behavior of bismuth (Bi) in photonic glasses for efficient Bismuth‐doped fiber and fiber lasers. Here, by engineering phosphorus and aluminum's topology, broadly tunable NIR emission has been realized in Bismuth‐doped phosphate laser glass. Structural and optical analyses on ²⁷Al magic‐angle spinning nuclear magnetic resonance (MAS NMR), ³¹P MAS NMR, fourier transform infrared (FTIR) and static emission spectra suggest that polymerization of glass network can be improved by proper addition of aluminum into the system, which can be evidenced by partial conversion of Q² to Q³ species of phosphorus and the shift of P–O–P asymmetric stretching vibration toward lower frequency, and this turns out beneficial to Bi NIR emission. Embedding aluminum tetrahedra into phosphorus glass network can reduce the local crystal field around bismuth and therefore lead to the blueshift of Bi emission. This work presents new insights into the luminescent behavior of Bi ions in phosphate glass and it helps the design and fabrication of Bismuth‐doped glasses and fibers in future.     

Impact of TeO2–B2O3 manipulation on physical,structural, optical and radiation shielding properties of Ho/Yb codoped mixed glass former borotellurite glass

In this work, (75-x)B₂O₃-xTeO₂-11Bi₂O₃–10Li₂O-1Ho₂O₃-3Yb₂O₃ (x = 10–60 mol%) mixed glass former (MGF) glasses were prepared by using the melt-quenching method to investigate the effect of mixed glass former between B₂O₃ and TeO₂ on the structural, optical and radiation shielding properties of glass. The amorphous nature of the glass samples was confirmed through XRD measurement. Optical ultraviolet–visible light (UV–Vis) spectroscopy revealed that the direct and indirect optical band gap (E_opt) decreased as TeO₂ content increased except for the anomaly at x = 30 mol% due to the interchanging dominance of bridging oxygen (BO) and non-bridging oxygen (NBO) in the glass network. Both direct and indirect refractive indices, n posted an increment except for x = 30 mol% due to polarizability influence of BO and NBO. Urbach energy, E_u declined thus indicating lesser disorder and less defects on the glass structure. The radiation shielding properties of the glass samples were determined for 15 keV–15 MeV photon energy range by using Phy-X/PSD software. Atomic number-dependent parameters such as mass attenuation coefficient (MAC) and effective atomic number (Z_eff) demonstrated an enhanced performances caused by higher Z of Te over B. Meanwhile, density-dependent parameters such as linear attenuation coefficient (LAC), mean-free path (MFP), half-value layer (HVL) and tenth-value layer (TVL) all exhibited an improvement over TeO₂ concentration due to higher density data obtained.     

Effect of topological structure on photoluminescence of PbSe quantum dot‐doped borosilicate glasses

Borosilicate glasses doped with PbSe quantum dots (QDs) were prepared by a conventional melt‐quenching process followed by heat treatment, which exhibit good thermal, chemical, and mechanical stabilities, and are amenable to fiber‐drawing. A broad near infrared (NIR) photoluminescence (PL) emission (1070‐1330 nm) band with large full‐width at half‐maximum (FWHM) values (189‐266 nm) and notable Stokes shift (100‐210 nm) was observed, which depended on the B₂O₃ concentration. The PL lifetime was about 1.42‐2.44 μs, and it showed a clear decrease with increasing the QDs size. The planar [BO₃] triangle units forming the two‐dimensional (2D) glass network structure clearly increased with increasing B₂O₃ concentration, which could accelerate the movement of Pb²⁺ and Se^2? ions and facilitate the growth of PbSe QDs. The tunable broadband NIR PL emission of the PbSe QD‐doped borosilicate glass may find potential application in ultra‐wideband fiber amplifiers.     

The origin of the heterogeneous distribution of bismuth in aluminosilicate laser glasses

As one kind of novel and burgeoning laser materials, bismuth‐doped silicate glasses have aroused increasing attention for the super broadband near‐infrared (NIR) emission. However, the large optical scattering loss, resulting from optical heterogeneity in glass color and refractive index, limits their further applications in telecommunication system. Thus, it is urgent to uncover the essence of heterogeneity in Bi‐doped silicate glasses and subsequently improve glass optical performance. It will give us some hint to homogenize the glass component and Bi active centers so as to boost the development of Bi‐based glass materials. Here, taking 1 typical Bi‐doped calcium aluminosilicate glass as an example, we revealed the origin of the optical heterogeneities in glass color and refractive index through the NIR emission spectra, electron probe microanalyzer (EPMA) of elements and X‐ray photoelectron spectroscopy (XPS) of Bi 4f_5/2, Bi 4f_7/2, and Al 2p. The inhomogeneous distribution of Bi and aluminum components is responsible for the heterogeneity in this glass system. In addition, we found that tetrahedral coordinated aluminum favors the existence of Bi NIR centers, consequently resulting in enhanced Bi NIR emissions. Furthermore, based on our results and the role of Al³⁺ in glass network, we demonstrate the homogenizing of glass component by finely tuning glass composition. This work will enrich the understanding of Bi‐doped laser glass and provide a guideline for the design of component‐derived Bi‐doped silicate glasses and fibers with efficient NIR emission and high optical quality.     

Near‐Infrared Broadband Photoluminescence of Bismuth‐Doped Zeolite‐Derived Silica Glass Prepared by SPS

Through the order–disorder transition process of zeolites, bismuth‐doped zeolite‐derived silica glasses with broadband near‐infrared (NIR) photoluminescence have been successfully prepared by spark plasma sintering (SPS). The samples were characterized by X‐ray diffraction, UV‐vis, photoluminescence, and fluorescence lifetime. The results showed that as‐prepared samples possessed favorable broadband NIR luminescence. The NIR emission (peaked at ~1140 nm) intensity decreased with increasing the bismuth doping concentration when excited by 500 and 700 nm. The tendency was different from the emissions (peaked at ~1240 nm) excited by 800 nm. In addition, the NIR fluorescence peaks of the fixed Bi concentration sample can be observed almost around 1140 or 1240 nm when excited by different wavelengths from 500 to 950 nm. These phenomena implied that the NIR emission peaked at different wavelengths may originate from different bismuth species. Three kinds of Bi active centers Bi⁺, Bi⁰, and (Bi₂)^2? were proposed to contribute to the NIR emission peaks at ~1140, 1240, and 1440 nm, respectively. Interestingly, a broadband NIR emission peaked at 1207 nm with a full‐width at half maximum of 273 nm was observed when excited by 600 nm, whose intensity was stronger than that excited by 800 nm. This property might be useful for broadband fiber amplifiers and tunable lasers.     

The optical band gap and the tailing states determination in glasses of TeO2-V2O5-K2O system

Ternary amorphous samples of 50TeO₂-(50 ? x)V₂O₅-xK₂O compositions with 0 ≤ x ≤ 20 (in mol %) have been prepared using the press-melt quenching method. The optical absorption spectra of glass have been recorded in the wavelength range 300–900 nm by UV-visible spectrophotometer. According to The Tauc and Urbach theories, the optical band gap and width of the tail of localized states have been evaluated. In addition the temperature glass transition (T _g ) of glasses have been determined by differential scanning calorimetry, confirming the amorphous nature of samples. The density and molar volume have been studied, indicating act of K₂O as network modifier.