Preparation and photoluminescence enhancement of Au nanoparticles with ultra-broad plasmonic absorption in glasses

The metal nanoparticles with ultra-broad localized surface plasmonic resonance (LSPR) absorption have been widely used to enhance the up conversion luminescence (UCL) of rare-earth doped nanoparticles. However, there have been no reports on the preparation of metal nanoparticles with the ultra-broad LSPR in the glasses. In this work, the gold nanoparticles with the ultra-broad LSPR were prepared for the first time in the rare-earth doped tellurite glasses by the high-temperature melting method, and the influence of ultra-broad LSPR on the UCL of Er³⁺–Yb³⁺ and Er³⁺–Yb³⁺–Nd³⁺ co-doped tellurite glasses was investigated upon 980 and 808 nm excitation, respectively. With the precipitation of the Au NPs, about seven and 12-fold enhancements were obtained for the green and red UCL of Er³⁺–Yb³⁺ co-doped tellurite glasses excited at 980 nm, respectively, and about 5.9 and sevenfold enhancements were observed for the green and red UCL of Er³⁺–Yb³⁺–Nd³⁺ co-doped tellurite glasses excited at 808 nm, respectively. The UCL mechanism related to UCL enhancement was confirmed. The results demonstrated that the enhanced excitation field and the increasing rate of radiative decay were responsible for the enhancement of UCL.     

Improved broadband near-infrared luminescence in Nd3+/Tm3+ co-doping tellurite glass with Ag NPs

The near-infrared (NIR) luminescence in S+E+O bands of tellurite glasses doped with Nd³⁺/Tm³⁺ and Ag nanoparticles (NPs) was investigated. The tellurite glasses were prepared by melt-quenching and heat-treated techniques. Under the excitation of 808 nm laser, Nd³⁺/Tm³⁺ doped tellurite glasses produced three NIR luminescence bands of 1.33, 1.47 and 1.85 μm, originating from Nd³⁺:⁴F_3/2→⁴I_13/2, Tm³⁺:³H₄→³F₄ and Tm³⁺:³F₄→³H₆ transitions respectively. Interestingly, a broadband luminescence spectrum ranging from 1280 to 1550 nm with the FWHM (full width at half maximum) about 201 nm was obtained due to the overlapping of the first two NIR bands. Further, the peak intensity of this broadband luminescence was increased by 75% after the introduction of Ag NPs with diameter in 10–20 nm. The analysis of fluorescence decay shows that compared with the enhanced local electric field, the energy transfer from Ag species to Nd³⁺ and Tm³⁺ ions plays a major role in luminescence enhancement. The findings in this work indicate that tellurite glass co-doped with Nd³⁺/Tm³⁺ and Ag NPs is a potential gain material applied in the S+E+O-band photonic devices.     

Embedding Ag or Au nanoparticles within the nano-sized wall of YbPO4:Er3+ inverse opals and resulting enhanced upconversion luminescence

Metal nanoparticles preparation in the interior of nanoscale skeleton of inverse opals made up of crystallized matrix is more difficult than the preparation of pure inverse opals. In the present work, the Ag or Au nanoparticles embedded YbPO₄:Er³⁺ inverse opals were prepared by a simple approach, which involved the infiltration of opal template by using the transparent YbPO₄:Er³⁺ sol including silver nitrate or chloroauric acid and the sintering at high temperature. The 20–30?nm Au or 5–10?nm Ag nanoparticles were formed in the interior of nanoscale skeleton in the YbPO₄:Er³⁺ inverse opals, and the Ag or Au nanoparticles embedded YbPO₄:Er³⁺ inverse opals were prepared. The influence of Ag or Au nanoparticles on the upconversion photoluminescence of YbPO₄:Er³⁺ inverse opal was studied, and the upconversion luminescence enhancement induced by the Ag or Au nanoparticles was observed. The mechanisms of upconversion luminescence enhancement of YbPO₄:Er³⁺ inverse opals induced by Ag or Au nanoparticles were discussed. The enhancement of upconversion luminescence induced by Ag nanoparticles was attributed to the enhancement of the excitation field, and the enhancement of upconversion emission induced by Au nanoparticles was related to the increasing of the radiation decay rate of Er³⁺.     

Photoluminescence Enhancement of SiO2‐Coated LaPO4:Eu3+ Inverse Opals by Surface Plasmon Resonance of Ag Nanoparticles

The surface plasmon resonance of Ag nanoparticles (NPs) and SiO₂ coating had been extensively employed to improve the photoluminescence (PL) intensity of nanomaterials. In the article, the LaPO₄:Eu³⁺ inverse opal photonic crystals were fabricated via combining a self‐assembly process with a sol–gel method. The SiO₂ shells were formed on the skeleton surface of LaPO₄:Eu³⁺ inverse opals and the Ag NPs were added into the voids of LaPO₄:Eu³⁺ inverse opals with the SiO₂ shells. The influence of the SiO₂ shells and Ag NPs on the PL of the LaPO₄:Eu³⁺ inverse opals were investigated. About sevenfold luminescence enhancement of LaPO₄:Eu³⁺ inverse opals was obtained by the coordination action of surface plasmon absorption effects of Ag nanoparticle and silica‐coating effects. The luminescence enhancement mechanisms of LaPO₄:Eu³⁺ inverse opals were discussed.     

Preparation and photoluminescence enhancement of Au nanoparticles embedded LaPO4:Eu3+ inverse opals

In this work, we present a facile preparation approach of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal photonic crystals. In the typical preparation process, the transparent LaPO₄:Eu³⁺ sol including HAuCI₄ was infiltrated into the opal templates. After the sintering, the 10‐20 nm Au nanoparticles were formed in the interior of nano‐sized wall of LaPO₄:Eu³⁺ inverse opal and the Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were obtained. The luminescence of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opal was investigated. The emission peaks located at the 593 (⁵D₀→⁷F₁), 618 (⁵D₀→⁷F₂) and 698 nm (⁵D₀→⁷F₄) from Eu³⁺ ions were observed. The 593, 618, and 698 nm emissions of Au nanoparticles embedded LaPO₄:Eu³⁺ inverse opals were enhanced in contrast to these of LaPO₄:Eu³⁺ inverse opal without the Au nanoparticles, which is from the excitation field enhancement caused by the localized surface plasmon resonance of Au nanoparticles.     

Preparation and Enhanced Luminescence of Au Nanoparticles Including SiO2:Tb3+ Three‐Dimensional Ordered Macroporous Films

Novel photoluminescent films consisting of three‐dimensionally ordered macroporous (3DOM) SiO₂:Tb³⁺ and Au nanoparticles were prepared by template assisted method, and their luminescence properties were investigated. The results show that Au nanoparticles have significant influence on luminescence property of SiO₂:Tb³⁺ 3DOM materials. The Au nanoparticles embedded in the skeleton of SiO₂:Tb³⁺ 3DOM materials could strongly improve their luminescence properties. The enhancement mechanism was discussed and demonstrated, which is attributed to the increasing of radiative decay rates of Tb³⁺ induced by surface plasmon effects of Au nanoparticles.     

Molecular‐Like Ag Clusters and Eu3+ Co‐Sensitized Efficient Broadband Spectral Modification with Enhanced Yb3+ Emission

AgNO₃/EuF₃/YbF₃ tri‐doped oxyfluoride glass was prepared by a melt‐quenching method, in which a high‐efficient broadband spectral modification can be realized due to the simultaneous energy‐transfer processes of Eu³⁺→Yb³⁺, molecular‐like Ag (ML‐Ag) clusters→Yb³⁺, and ML‐Ag clusters→Eu³⁺→Yb³⁺. The spectral measurements indicated that besides the F‐center brought by the fluorides, the formation of the ML‐Ag clusters and the evolution of silver species within the glass matrix were also closely related to the introduction of Eu³⁺ and Yb³⁺ ions and which in return greatly affected the luminescence properties of these rare‐earth ions. As the UV‐visible irradiation in the wavelength region of 250–600 nm can be efficiently converted into near‐infrared emission around 1000 nm in the AgNO₃/EuF₃/YbF₃ tri‐doped glass, which thus has promising application in enhancing the photovoltaic conversion efficiency of the silicon solar cell.     

Photoluminescence of Ag Nanoparticles and Tm3+ Ions in the Bismuth Germanate Glasses for the Blue Light‐Excited W‐LED

Materials containing rare‐earth ions and Ag nanoparticles (NPs) have been widely applied due to prior demonstration of increase in their luminescence properties. Here, Tm³⁺ ions‐doped bismuth germanate glasses were synthesized by a chemical reduction method based on the conventional melting‐quenching technique. The Ag NPs were facilely precipitated in the glass matrix by the chemical reduction method during the annealing process. TEM image shows that the Ag NPs are closely dispersed in the glass matrix. The luminescence properties and energy‐transfer mechanism were systematically investigated by means of absorption, emission, and excitation spectra. Significant enhancements of Tm³⁺ ions emission and a broad emission band centered at 568 nm caused by Ag NPs are observed upon 474‐nm excitation. Our research may illustrate the interactions between Tm³⁺ ions and Ag NPs and provide a simplified way to synthesize the high‐efficiency luminescent materials for the blue light‐excited W‐LEDs.     

Selective preparation of Ag species on photoluminescence of Sm3+ in borosilicate glass via Ag+-Na+ ion exchange

Photoluminescence (PL) of rare earth ion-doped glasses could be enhanced by diverse Ag species such as Ag⁺ ions, Ag⁺-Ag⁺ pairs, Ag nano-clusters (NCs), and Ag nanoparticles (NPs). Selective preparation of silver species in rare earth ion-doped glasses is a crucial step to obtain the luminescence enhancement of rare earth ions caused by the different silver species. In this work, Ag⁺ ions and Ag NCs were selectively prepared in the Sm³⁺-doped borosilicate glass via the Ag⁺-Na⁺ ion exchange. The influence of AgNO₃/NaNO₃ ratio in the molten salt on the Ag existing states was investigated. The results demonstrate that the isolated Ag⁺ ions exist in the Sm³⁺-doped borosilicate glass when the ratio of AgNO₃/NaNO₃ is 1/1000. The Ag NCs are formed in the Sm³⁺-doped borosilicate glass when the AgNO₃/NaNO₃ ratio is 1/10. The influence of Ag⁺ ions or Ag NCs on the PL of Sm³⁺ was systematically investigated. The results show that the PL of Sm³⁺ was enhanced by the energy transfer from Ag⁺ ions or Ag NCs to Sm³⁺.     

High Nd3+→Yb3+ energy transfer efficiency in tungsten‐tellurite glass: A promising converter for solar cells

This work reports on the energy transfer efficiency for Nd³⁺/Yb³⁺ co‐doped tellurite glasses (80TO₂‐20WO₃, in mol%,). The correlation between Yb³⁺ ion concentration and the downconversion mechanism was investigated using optical and thermal lens spectroscopies, which enabled investigation of the radiative and nonradiative processes, respectively, involved in energy transfer from neodymium to ytterbium. The Nd³⁺ near‐infrared fluorescence disappeared almost entirely when the maximum concentration of Yb³⁺ ions (4 mol%) was doped into the host. In contrast, there was a corresponding increase in the ytterbium emission at around 980 nm. When ytterbium was added, there was also a simultaneous reduction in the amount of heat generated by the sample due to a reduction in the nonradiative decay rate, corroborating the suspected high energy transfer efficiency of Nd³⁺→Yb³⁺. The results indicate that tungsten‐tellurite glasses may be of potential use in solar cells for matching the solar emission spectrum to the semiconductor cell.     

Enhanced non-linear optical properties of Eu3+ activated glasses by embedding silver nanoparticles

Tri-positive lanthanide ion (Eu³⁺) activated glasses doped with different concentrations of silver (Ag0₎ nanoparticles obtained using thermal reducing agent were fabricated by applying the method of melt quench. The formation of Ag⁰ nanoparticles in glasses was revealed by the surface plasmon resonance (SPR) peak in the absorption spectra. Transmission electron microscopic measurements confirmed the presence of spherically shaped Ag⁰ nanoparticles of different size distribution. The absorption spectra showed a red–shift of the SPR peak with an increase in AgNO₃ concentration occurring through Ostwald's ripening process because of the growth of particle size (as evidenced from microscope images). The non-linear optical (NLO) and optical limiting measurements were performed in the near infrared spectral region and femtosecond pulse excitation. The non-linear parameters were found to increase as the AgNO₃ concentration increased to 0.6 mol %, however, the parameters subsequently decreased at higher doping level. The optical limiting threshold values demonstrated a reverse trend. The increase in non-linear optical properties regarding Ag nanoparticles concentration attributed to the enhancement of polarizabilities of glasses that occurred through local field stimulated by SPR of Ag nanoparticles when exposed to laser radiation of high energy. The increase in NLO coefficients (particularly the non-linear absorption coefficient) and the decrease in optical limiting threshold values with AgNO₃ concentration (up to 0.6 mol %) indicated that these glasses containing 0.6 mol % AgNO₃ are useful for the construction of the power optical limiters that function at the infrared region in the femtosecond pulse regime.     

Effective sensitization of Eu3+ ions on Eu3+/Nd3+ co-doped multicomponent borosilicate glasses for visible and NIR luminescence applications

Eu³⁺/Nd³⁺ co-doped multicomponent borosilicate glasses (ND1E: 10BaO +10ZnF₂+10K₂O +20SiO₂+(49-x) B₂O₃+1Nd₂O₃+xEu₂O₃) were prepared by conventional melting and rapid quench technique to evaluate the effect of Eu³⁺ ions in the Nd³⁺ doped glasses. Thermal stability, structural and spectroscopic characteristics of the ND1E glasses were investigated by using DSC, XRD, FTIR, Optical absorption, excitation and emission measurements. The Judd – Ofelt (JO) analysis is implemented to the absorption spectrum of the prepared glassy matrix in order to identify their potential applicability in lasing devices. Enhancement of ⁷F₀ → ⁵L₆ band (394 nm) with the increasing concentration of Eu³⁺ ion in the Nd³⁺ excitation spectra (λ_emi = 1060 nm) reveals the possibility of obtaining the characteristic fluorescence spectra of Nd³⁺ ion with the typical excitation wavelengths (Nd³⁺ = 584 nm and Eu³⁺ = 394 nm) of both rare earth ions and it is further verified from the emission spectrum. This interesting luminescence effect of showing excellent visible and NIR emission under 394 nm excitation mainly attributes the energy transfer mechanism between the RE³⁺ ions and the reason underlying this effect is discussed in detail with the help of partial energy level diagram. Energy transfer efficiency between the Eu³⁺ and Nd³⁺ ions were evaluated by using the radiative lifetimes of the prepared glasses. Also, a comparison of radiative properties and lasing characteristics of Eu³⁺/Nd³⁺ co-doped glasses with other Nd³⁺ glasses are reported. The emission intensities were characterized using CIE chromaticity diagram and the observed CIE coordinates shows a shift towards reddish – orange region with the increase in Eu³⁺ concentration. The quantum efficiency of the prepared glasses was determined experimentally. The obtained results suggest that the ND1E glassy system can be considered as a potential candidate for visible and NIR luminescence applications.     

A Novel Blue‐Emitting Phosphor of Eu2+‐Activated Magnesium Haloborate Mg3B7O13Cl

Eu²⁺‐doped magnesium haloborate Mg₃B₇O₁₃Cl was synthesized by the conventional high‐temperature solid‐state reaction. The phase formation was confirmed by X‐ray powder diffraction (XRD) measurements and structure refinement. The photoluminescence excitation and emission spectra, and decay curves were measured. Under the excitation of near‐UV light, Eu²⁺‐doped Mg₃B₇O₁₃Cl presents a narrow blue‐emitting band centered at 423 nm. The maximum absolute quantum efficiency (QE) of Mg₃B₇O₁₃Cl:Eu²⁺ phosphor was measured to be 80% excited at 385 nm light at 300 K. The thermal stability of the blue luminescence was evaluated by the luminescence decays as a function of temperature. The phosphor shows an excellent thermal stability on temperature quenching effects. Moreover, Mg₃B₇O₁₃Cl:Eu²⁺ phosphor shows scintillation characteristics excited by X‐ray irradiation at room temperature and presents a blue luminescence band with a fast lifetime of 600 ns.     

Synthesis of LaOF:Eu3+ Nanoparticles with Strong Luminescence Enhanced by Organic Ligands

LaOF:Eu³⁺ nanoparticles were successfully prepared by annealing LaF₃:Eu³⁺ nanocrytsals which were capped with SiO₂ shell. The SiO₂ shell effectively prohibited the growth of LaF₃:Eu³⁺ nanocrystals during the annealing process, and it was etched off after annealing to obtain the LaOF:Eu³⁺ nanoparticles. The LaOF:Eu³⁺ nanoparticles had a size comparable to the original LaF₃:Eu³⁺ nanoparticles. Inorganic–organic hybrid nanoparticles of LaF₃:Eu³⁺ and LaOF:Eu³⁺ nanoparticles with thenoyltrifluoroacetone (TTA) ligands were prepared. Strong luminescence as a result of the energy transfer from the TTA organic ligands to the LaF₃:Eu³⁺ and LaOF:Eu³⁺ nanoparticles was observed. The LaOF:Eu³⁺‐based hybrid nanoparticles exhibited stronger luminescence intensity and broader excitation spectral range than the LaF₃:Eu³⁺‐based hybrid nanoparticles. Effect of the content of TTA ligands on the luminescence of the LaOF:Eu³⁺ nanoparticles was investigated in detail.     

Effects of In2O3 nanoparticles doping on the photoluminescent properties of Eu2+/Eu3+ ions in silica glasses

Eu²⁺/Eu³⁺ ions doped silica glasses contained In₂O₃ nanoparticles (NPs) have been fabricated by using nanoporous silica glasses. Interestingly, efficient energy transfer from In₂O₃ NPs to Eu²⁺/Eu³⁺ ions enhanced the photoluminescence (PL) emission of Eu²⁺/Eu³⁺ ions, which derives from lattice defects in In₂O₃ NPs. Our work has not only demonstrated a facile way to fabricate NPs and rare earth ions co-doped silica glasses, but also extended the applications of semiconductor oxide NPs such as In₂O₃ NPs.     

Investigation of optical properties: Eu with Al codoping in aluminum silicate glasses and glass‐ceramics

Eu‐doped transparent oxyfluoride aluminosilicate glass was prepared by controlling with Al codoping of melt‐quenched glass fabricated under air atmosphere. In the presence of Al input, the photoluminescence emission spectra under 393 nm excitation shows a blue shift by adjusting the ratio of Eu³⁺ and Eu²⁺. After heat treatment of glass, the ratio of Eu³⁺ and Eu²⁺ of luminescence emission were changed by controlling treatment temperature. The PL intensity of Eu³⁺ and Eu²⁺ ions in the glass‐ceramics (GC) was much stronger than in the precursor glass (PG). The possible mechanism responsible for color tuneability of the ratio of Eu³⁺ and Eu²⁺ doped was discussed.     

Eu‐, Tb‐, and Dy‐Doped Oxyfluoride Silicate Glasses for LED Applications

Luminescence glass is a potential candidate for the light‐emitting diodes (LEDs) applications. Here, we study the structural and optical properties of the Eu‐, Tb‐, and Dy‐doped oxyfluoride silicate glasses for LEDs by means of X‐ray diffraction, photoluminescence spectra, Commission Internationale de L'Eclairage (CIE) chromaticity coordinates, and correlated color temperatures (CCTs). The results show that the white light emission can be achieved in Eu/Tb/Dy codoped oxyfluoride silicate glasses under excitation by near‐ultraviolet light due to the simultaneous generation of blue, green, yellow, and red‐light wavelengths from Tb, Dy, and Eu ions. The optical performances can be tuned by varying the glass composition and excitation wavelength. Furthermore, we observed a remarkable emission spectral change for the Tb³⁺ single‐doped oxyfluoride silicate glasses. The ⁵D₃ emission of Tb³⁺ can be suppressed by introducing B₂O₃ into the glass. The conversion of Eu³⁺ to Eu²⁺ takes place in Eu single‐doped oxyfluoride aluminosilicate glasses. The creation of CaF₂ crystals enhances the conversion efficiency. In addition, energy transfers from Dy³⁺ to Tb³⁺ and Tb³⁺ to Eu³⁺ ions occurred in Eu/Tb/Dy codoped glasses, which can be confirmed by analyzing fluorescence spectra and energy level diagrams.     

Influence of the Eu2+ on the Silver Aggregates Formation in Ag+–Na+ Ion‐Exchanged Eu3+‐Doped Sodium–Aluminosilicate Glasses

Europium‐doping sodium–aluminosilicate glasses are prepared by melt‐quenching method, in which europium ions were spontaneously reduced from their trivalent to divalent state. The silver was introduced into glasses by Ag⁺–Na⁺ ion exchange and the interactions between europium ions and silver species were investigated. Owing to energy transfer (ET) from Ag⁺/silver aggregates to Eu³⁺, significant enhancements of Eu³⁺ emission were observed for 285/350‐nm excitation, respectively. The divalent europium ions promote the formation of silver aggregates in the process of ion exchange.     

Simultaneous enhancement of quantum cutting luminescence in Er-doped NaBaPO4 phosphors by crystal field control and plasmonic modulation

It is of great significance to enhance the quantum-cutting (QC) luminescence for practical applications due to the narrow absorption cross-section and low luminescence efficiency of rare earth ions. In this work, NaBaPO₄:Er³⁺ phosphors doped with Li⁺ were synthesized through a solid-state reaction. The QC luminescence of NaBaPO₄:Er³⁺ phosphor was enhanced 5.71 times by doping Li⁺. XRD patterns and Judd-Ofelt calculations demonstrated the crystal field distortion when introduced Li⁺, which would increase the transition probability of Er³⁺. Furthermore, NaBaPO₄:Er³⁺, Li⁺ phosphors were decorated with silver nanoparticles (Ag NPs). The effect of Ag NPs on QC luminescence was studied, and the results showed that QC luminescence was further enhanced up to 1.95 times by Ag NPs. FDTD simulations revealed that Ag NPs generated substantial surface plasmons, which would boost the excitation rate of Er³⁺. Our studies would provide a useful strategy to enhance QC luminescence, which has potential application in germanium-based solar cells.     

Chemical,biological, and antibacterial characterization of silica glass containing silver and gold nanoparticles

The aim of this study has been the preparation of sol‐gel glasses with potential antibacterial properties. Bioactive glasses containing different percentages of silver and gold nanoparticles have been synthesized via the sol‐gel method. The obtained glasses have 0.5, 1, 1.5, and 2 wt% silver as well as a constant amount of gold nanoparticles (AuNP) added as colloidal solution (15 wt%). Fourier Transform Infrared (FTIR) spectroscopy was used to characterize the materials. Scanning electron microscopy (SEM) has been used to investigate the surface of each sample. Moreover, the materials have been characterized in order to verify their antibacterial activities as well as their bioactivity and cytocompatibility as a function of Ag and Au content. SEM/EDX analysis has shown that the samples are bioactive because they are able to stimulate hydroxyapatite nucleation on their surface when soaked in a simulated body fluid (SBF). WST‐8 assay of 3T3 cells, placed in contact with the material extracts, has showed that the glass does not induce cytotoxicity. Staphylococcus epidermidis and Pseudomonas aeruginosa strains have been used for the evaluation of the antibacterial properties of each sample. The experimental data have shown that all synthesized materials have antibacterial activity. However, the two bacterial strains respond differently to the materials. The data show that the presence of AuNP causes a decrease in the antibacterial activity of Ag⁺ ions.