AbstractControlled morphology modulation of graphene carbon nitride (g-C3N4) is successfully realized from bulk to 3D loose foam architecture via the blowing effect of a bubble, which can be controlled by heating rate. The loose foam network is comprised by spatially scaffolded few-atom-layer interconnected flakes with the large specific surface area, as supporters to prevent agglomeration and provide a pathway for electron/phonon transports. The photocatalytic performance of 3D foam strutted g-C3N4 toward RhB decomposition and hydrogen evolution is significantly enhanced with the morphology optimization while its excellent optoelectronic properties are maintained simultaneously. Herein, the ultrathin, mono-, and high-quality foam g-C3N4 interconnected flakes with controlled layer are facilely obtained through ultrasonic, thus overcoming the drawbacks of a traditional top–down approach, opening a wide horizon for diverse practical usages. Additionally, the layer control mechanism of 3D hierarchical structure has been explored by means of bubble growth kinetics analysis and the density functional theory calculations.

•Magnetic and fluorescent sub-10 nm Ni-doped ZnAl2O4 nanocrystals are synthesis by facile hydrothermal method.•Ni dopant is demonstrated to be the origin of the obtained ferromagnetism and fluorescence.•A broad band (1.1–1.4 μm) emission is achieved fully covering the NIR-II optimal bio-imaging window.Nanocrystals with combined properties of magnetic and fluorescence are considered as “multifunctional materials” or “smart materials” which have promising biological applications including dual-modal imaging, biological research, targeted drug delivery, clinical diagnostics and therapeutics. Utilizing a green hydrothermal method, magnetic nanocrystals Ni-doped ZnAl2O4 with broadband emission at ∼1200 nm have been developed as a new type of multifunctional material. The obtained ultrasmall nanocrystals in sub-10 nm range are more easily for body clearance and less toxicity in theory. Ni ions are demonstrated distribute homogeneously in +2 valance state, which provides ferromagnetism in the diamagnetic matrix of ZnAl2O4. Under the excitation of 670 nm, the whole broad emission band centered at 1200 nm fully covers the second near-infrared window (1.1–1.4 μm). These ultrasmall Ni-doped ZnAl2O4 nanocrystals with magnetic-fluorescent multifunctionality open a door to more efficient and safer biological probes.Sub-10 nm Ni-doped ZnAl2O4 nanocrystals synthesized by hydrothermal method exhibit both magnetic and fluorescent properties. A broad band emission centered at 1200 nm is obtained, fully covering the second near-infrared window (1.1–1.4 μm). The realization of multifunctional magnetic-fluorescent nanocrystals is expected to have potential important applications in dual-modal imaging, biological research, targeted drug delivery, clinical diagnostics and therapeutics.Download high-res image (182KB)Download full-size image

All solid-state PbS quantum dot (QD)-doped glass fibers with tunable near-infrared (NIR) emission were successfully fabricated by using the “melt-in-tube” method for the first time. The precursor fibers were first prepared without any obvious element diffusion or crystallization by drawing the fiber preform at a heating temperature at which the fiber core was already melted while the fiber cladding was softened. Then the PbS QDs were precipitated evenly in the matrix of the glass fiber core after a careful heat treatment at low temperature. From the PbS QD-doped glass fibers, intense wavelength-tunable broad NIR emission bands were observed upon excitation with an 808 nm laser. The transmission loss of the fibers can be reduced by further matching the thermal expansion of the fiber core and cladding glass. Therefore, after further optimizing the composition and optical properties of the PbS QD-doped glass fiber, it is expected to be a potential gain medium for the development of wavelength-tunable lasers and broadband fiber amplifiers. More importantly, the melt-in-tube method exhibits a feature of completely controllable crystallization in the fiber formation process, which would open a new route for fabricating novel functional QD-doped glass fibers.

We demonstrated remarkably enhanced 2.7 μm emission in glass-ceramic (GC) fibers containing NaYF4:Er3+ nanocrystals with 980 nm excitation for the first time. The melt-in-tube technique is of scientific and technical significance for the fabrication of GC fibers in comparison to the conventional rod-in-tube technique. The obtained precursor fibers, in which the structure can be maintained well, exhibit no obvious element diffusion or crystallization during the fiber-drawing process. After a careful heat treatment, NaYF4 nanocrystals were controllably precipitated in the glass fiber core. Owing to the incorporation of Er3+ ions into the low phonon energy NaYF4 nanocrystals, enhanced 2.7 μm emission was achieved from the Er3+-doped GC fibers, which was almost undetectable in precursor fibers due to the high phonon energy of the borosilicate glass fiber matrix. Moreover, the 2.7 μm emission lifetime was obtained due to the excellent emission properties of Er3+ in the GC fibers. The transmission loss values of precursor fibers and GC fibers at 1310 nm were measured to be 7.44 dB m−1 and 11.81 dB m−1, respectively. In addition, a theoretical simulation based on the rate equations and propagation equations was performed to evaluate the possibility of 2.7 μm laser output. The excellent optical properties endow the GC fibers with potential applications for mid-infrared fiber lasers.

Graphite-like carbon nitride (g-C3N4) modified with different non-metal ions (boron and sulfur) was synthesized by directly heating a mixture of melamine and dopant with a continuous doping concentration. The effect of the doping ion and its concentration on the structural and optical properties of the samples were investigated in detail. Surprisingly, with the doping concentration increasing, an unexpected relative blue shift was determined in the photoluminescence (PL) spectra of the doped g-C3N4, showing an enhancement in the bandgap which is not in agreement with the typical red shifts in the PL spectra of no-metal ion-doped g-C3N4. To investigate this interesting variation in PL, density functional theory (DFT) has been used and a possible mechanism for the non-metal ion-modified g-C3N4 system was proposed. It is supposed that the blue shift of the non-metal ion-doped g-C3N4 could be mainly attributed to the doping-induced electronic redistribution and structural reconstruction.

Nonlinear optical (NLO) effects originating from materials doped with rare-earth ions possess colossal potential for application in all-optical switches. However, among previous studies, Er3+ ion-doped glass ceramics (GCs) with remarkable NLO features have been investigated with respect to optical modulation applications by tailoring their nonlinear transmittance upon excitation at various near-infrared (NIR) wavelengths, which might prove to be a simple way of achieving “on–off” optical modulation in future all-optical switches. Here, we present the first observation of tailorable nonlinear transmittance in germanate oxyfluoride GCs containing Er3+:LaF3 nanocrystals, manipulated by excitation at 808, 980, and 1550 nm, which is consistent with the results from theoretical calculations and simulations. Furthermore, we conduct experimental investigation and analysis related to energy level transitions and dynamical evolution, indicating that these intriguing NLO features can be attributed to the differentiation between excited state absorption accompanied by up-conversion luminescence and stimulated emission processes during excitation at discrepant NIR wavelengths. Importantly, bidirectional optical switching for the “on–off” toggle effect has been successfully demonstrated by selectively tailoring the nonlinear transmittance of the single Er3+-doped GCs. This tailorable NLO behavior of Er3+-doped GCs, which is dependent on excitation at different NIR wavelengths, might provide a versatile strategy for the development of next-generation bidirectional all-optical switches.

Nanorod-like Zn2GeO4 and diverse Zn2GeO4:xEu nanostructures were controllably synthesized via a surfactant-free hydrothermal route. Detailed composition and morphology were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The influence of Eu3+-doping on the phase and size transition of Zn2GeO4 nanocrystals was investigated, and a possible Zn2GeO4:xEu crystal growth mechanism, which is ascribed to hetero-valence ion doping, is proposed. Photoluminescence (PL) spectra indicate that Zn2GeO4:xEu phosphors give both the bluish-white emission from the Zn2GeO4 host and orange-red emission of Eu3+ ions. The morphologies of calcined Zn2GeO4:xEu were studied and their PL properties were also investigated. The results suggested that the emission of both the Zn2GeO4 host and Eu3+ ions can be adjusted via tuning the concentration of Eu3+-doping, excitation wavelengths and calcination schedules of the Zn2GeO4:xEu nanocrystals. Therefore, Zn2GeO4:Eu nanocrystals with multi-color as well as white light emission displayed a potential application for white light-emitting diodes.

Non-agglomerated and uniform Eu3+-doped NaGdF4 nanocrystals were synthesized via a facile one-step precipitation method at room temperature. Under pulsed magnetic fields, the luminescence properties of the as-prepared samples have been recorded and discussed in detail. Particularly, “controllable eliminating luminescence” of 5D0–7F0 transition in Eu3+ was achieved during the magneto-optical interaction. Magnetic field assisted cross-relaxation of excited electrons was derived from Zeeman splitting of the higher 5D energy level, and the magnetic confinement of f electron wave functions was proposed which were responsible for the change in luminescence intensity with a variation of magnetic field strength. The characteristic variation of the emission band under pulsed magnetic fields promises an optical probe for magnetic field detection.

Monodisperse rice-like Ni2+-doped β-Ga2O3 nanostructures were phase-controllably synthesized via a hydrothermal route and subsequent calcination. The detailed phase, composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), which showed that the rice-like β-Ga2O3 nanostructures were assembled with nanorods with a diameter of ∼50 nm along their entire length. The phase formation and transition behavior of β-Ga2O3 nanocrystals were investigated, and a possible crystal growth mechanism for the rice-like GaOOH nanostructure was proposed. Photoluminescence (PL) spectra indicated that Ni2+-doped β-Ga2O3 phosphors exhibit a broadband near-infrared emission (1200–1600 nm). Besides, the magnetic properties were also investigated, revealing the ferromagnetic nature of the Ni2+-doped β-Ga2O3 nanocrystals. The single phase Ni2+-doped β-Ga2O3 nanocrystals endowed with optical and magnetic bifunctional properties have promising potential application in the fields of optical communication, biological diagnosis and magnetic information storage, etc.

We synthesized NaNbO3 micro/nano-crystals with six morphologies and three different crystal structures using the hydrothermal method. Each single hexagonal NaNbO3 micro/nano-crystal (samples No. 1–3) exhibited a strong second-order nonlinear response. By calculating the average intensity and measuring the polarization response of each of these hexagonal crystals (samples No. 1–3), it was demonstrated that the same crystal structure displays a similar optical second harmonic generation (SHG) response. Furthermore, SHG was shown to be independent of the morphology and identical for similar crystals, which is expected for a volume effect with a second-order susceptibility tensor depending on the properties of the material. The optical SHG properties of these NaNbO3 micro/nano-crystals together with the previous related research suggest that these non-toxic crystals may find promising applications in biological imaging and related fields.

The direct and effective synthesis of PbS quantum dots (QDs) in a solid-state matrix is of great importance in the production and application of PbS QDs photonic devices. The present article describes the direct precipitation of PbS QDs in an inorganic glass matrix by the irradiation of a femtosecond (fs) laser. It has been demonstrated that the formation of the QDs is strongly influenced by the thermal effect of the fs laser. The effect of the irradiation parameters and of Ag clusters on the precipitation of QDs has been investigated, in addition to the spatial distribution of the QDs in the irradiated area, and a mechanism is suggested. The confocal Raman spectra indicate that after irradiation the concentration of the QDs is the highest at the center. On the other hand, heat treatment of the irradiated sample has also been carried out to adjust the size, distribution and photoluminescence of QDs within the glass matrix. The electron probe microanalyzer (EPMA) has provided direct evidence for the large change in refractive index and for the ring-shaped structure formed on irradiation. Based on selective local control of the PbS QDs, a waveguide demonstration has been conducted to illustrate the feasibility of directly writing a PbS QDs waveguide with an fs laser in a glass matrix.

Up-conversion (UC), harvesting near-infrared (NIR) sunlight, is highly desirable for photovoltaic (PV) cells. In regard to this concept, most of the reported experiments on UC materials and their applications, however, were conventionally studied on a monochromatic laser with a narrow excitation band, which is difficult to meet the requirement of solar spectrum conversion. Given the practical applications in PV cells, investigations for UC materials upon simultaneous multiwavelengths even broadband near-infrared (NIR) sunlight excitation are much more meaningful. Herein, we studied the UC luminescence properties of germanate oxyfluoride glass ceramics (GCs) containing LaF3:Er3+ nanocrystals with lower phonon energy upon simultaneous triwavelength excitation. The UC emission intensities upon simultaneous triwavelength excitation were drastically enhanced in comparison with the case of that by monochromatic excitation. The UC luminescence mechanisms were interpreted in-depth in terms of synergetic UC effect owing to the perturbation in the excited states established by different excitation wavelengths. We demonstrated the application of the simultaneous triwavelength excited GC by adding it to the rear face of thin-film hydrogenated amorphous silicon (a-Si:H) solar cells. The photoactive current generated by the reflected UC light upon simultaneous triwavelength excitation was dramatically enhanced in contrast to the case of that upon monochromatic excitation. This Er3+-doped germanate oxyfluoride GC, harvesting broader NIR sunlight photons via simultaneous multiwavelength excitation, has colossal potential to improve the power conversion efficiency in PV cells in the near future.

•Pure orthorhombic Sr2CeO4:Yb3+, M+ (M+=Li+, Na+, K+) were successfully synthesized.•The structural and photoluminescence of these samples were characterized by XRD and fluorescence spectrometer.•The effect of Li+/Na+/K+ on the properties of samples had been researched and the relevant mechanisms have been discussed in detail.•These NIR materials could have potential application in the high efficiency silicon-based solar cells.NIR luminescence phosphors Sr2CeO4:Yb3+, M+ (M+=Li+, Na+, K+) were synthesized by conventional solid-state method in the present paper. The prepared phosphors are characterized by XRD and fluorescence spectrometer. Under UV light excitation, the NIR emission intensity of Yb3+:2F5/2→2F7/2 around 1 μm of Sr2CeO4:Yb3+ is strengthened significantly by introducing appropriate alkali metal cations dopants (Li+, Na+, K+) into the crystalline lattice. The relevant mechanisms have been discussed in detail. The peculiar optical properties make Sr2CeO4:Yb3+, M+ (M+=Li+, Na+, K+) promising for potential application in the high efficiency silicon-based solar cells.

•PbS quantum dot (QD) was prepared in silicate glasses through post annealing.•Tunable near-infrared photoluminescence was obtained in PbS QD-embedded glasses.•Optical amplification was simultaneously achieved at both 1330 and 1550 nm windows.Optical properties of PbS quantum dot (QD)-embedded silicate glasses prepared through post annealing were investigated. By modulating the heat treatment condition, tunable near-infrared (NIR) photoluminescence (PL) was obtained. Noticeable optical amplification was achieved at both 1330 nm and 1550 nm windows with similar amplification characteristics in single PbS QD-embedded glass, which indicated that broadband optical amplification is expected at the entire PL band of PbS QD-embedded glass. The PbS QD-embedded glass with multi-wavelength optical amplification is promising as the gain medium of broadband fiber amplifiers and tunable fiber lasers.

•The ways to modulate electronic structure of g-C3N4 are discussed.•The photocatalytic to photoelectronic applications of g-C3N4 are summarized.•We discuss the pathways to improve photocatalytic and photoelectronic properties.•The correlation of electronic structure and photoelectronic properties is founded.As an analog of graphite, graphitic carbon nitride (g-C3N4) has been the hotspot in the materials science for its unique electronic structure. With medium band gap as well as thermal and chemical stability in ambient environment, it becomes one of the most promising photocatalytic materials. Intensive investigation has been focus on its photocatalytic performance for various reactions to date. What is more, controllable modulation of its electronic structure via doping or chemical functionalization is available. In addition, considerable attention has been paid on its photoelectronic application, such as light emitting device, photocathode, optical sensor, etc. Based on the electronic properties and pathway to modulate its electronic structure, in this review, we highlight the applications of g-C3N4 ranging from photocatalytic to photoelectronic materials.

By finely tuning the electrospun parameters (feeding rate of solution, working voltage and distance, etc.) and concentration of inorganic salts, various ZnAl2O4 nanostructures (nanoparticles, nanonecklaces, nanofibers, nanotubes and hollow micromelts) were controllably synthesized by a single-nozzle electrospinning technique. The formation mechanisms of different ZnAl2O4 nanostructures, including ‘oriented attachment’ mechanism, ‘gas-push’ mechanism, etc., were proposed to elucidate the morphology of the nanostructures and microstructure evolvement process. The morphology and microstructure of calcined electrospun nanostructures were considered to be mainly dependent on two factors, i.e. concentration of inorganic salts and size of as-prepared electrospun nanofibers. Using Ni2+ ions as activators, broadband near infrared (NIR) emission covering 1000–1400 nm peaking at about 1176 nm was detected in Ni2+-doped ZnAl2O4 nanostructures. The broadband NIR emission at around 1.3 μm optical communication window with a long lifetime of ∼640 μs makes Ni2+-doped ZnAl2O4 nanostructures as a promising candidate for micro/nano-broadband optical amplifiers, fibers, etc.

MCM-48 nanoparticle-embedded polymer nanofibers (NPNFs) were prepared from the PVP solution containing MCM-48 nanoparticles (NPs) by the electrospinning technique. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) were used to characterize the composition and morphology of electrospun nanofibers. The results showed that the average diameter of MCM-48 NPNFs was about 500 nm. Photoluminescence (PL) and phosphorescence properties were investigated by fluorescence spectrofluorometer. MCM-48 NPNFs exhibited a bright blue-green emission at ∼420 nm, followed by a long-lifetime blue-green phosphorescence at ∼480 nm, which can be fitted by a bi-exponential decay process with lifetimes of 3.24 s and 1.22 s at room temperature. The triplet-to-singlet transition is responsible for the blue-green emission around 420 nm of the MCM materials, while the phosphorescence at ∼480 nm is probably due to the oxygen-related vacancies on the surface, which act as a capture trap.

Yttrium aluminum garnet Y3Al5O12 (YAG):Er3+,Tm3+ phosphor powders with preferable luminescent properties and nanocrystals with better morphology were synthesized by the solid-state reaction method and coprecipitation method, respectively. The composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), which showed that the nanocrystals were pseudomonodispersed with the particle size of ∼30 nm. Photoluminescence (PL) spectra indicated the 2.7 μm emission of Er3+ was remarkably enhanced via Tm3+ sensitization, and a novel circulatory energy transfer mechanism was proposed. A novel dehydration method was used to decrease the contents of the hydroxyl group (OH–) confirmed by photoluminescence spectra and Fourier transform infrared spectra (FTIR). YAG crystallites were introduced into tellurate glass and formed to glass composites with good optical performance. These nanocrystals–glass composites open a brand new field for the research of mid-infrared laser materials.

Monodisperse rice-like Ni2+-doped β-Ga2O3 nanostructures were phase-controllably synthesized via a hydrothermal route and subsequent calcination. The detailed phase, composition and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), which showed that the rice-like β-Ga2O3 nanostructures were assembled with nanorods with a diameter of ∼50 nm along their entire length. The phase formation and transition behavior of β-Ga2O3 nanocrystals were investigated, and a possible crystal growth mechanism for the rice-like GaOOH nanostructure was proposed. Photoluminescence (PL) spectra indicated that Ni2+-doped β-Ga2O3 phosphors exhibit a broadband near-infrared emission (1200–1600 nm). Besides, the magnetic properties were also investigated, revealing the ferromagnetic nature of the Ni2+-doped β-Ga2O3 nanocrystals. The single phase Ni2+-doped β-Ga2O3 nanocrystals endowed with optical and magnetic bifunctional properties have promising potential application in the fields of optical communication, biological diagnosis and magnetic information storage, etc.

Graphite-like carbon nitride (g-C3N4) modified with different non-metal ions (boron and sulfur) was synthesized by directly heating a mixture of melamine and dopant with a continuous doping concentration. The effect of the doping ion and its concentration on the structural and optical properties of the samples were investigated in detail. Surprisingly, with the doping concentration increasing, an unexpected relative blue shift was determined in the photoluminescence (PL) spectra of the doped g-C3N4, showing an enhancement in the bandgap which is not in agreement with the typical red shifts in the PL spectra of no-metal ion-doped g-C3N4. To investigate this interesting variation in PL, density functional theory (DFT) has been used and a possible mechanism for the non-metal ion-modified g-C3N4 system was proposed. It is supposed that the blue shift of the non-metal ion-doped g-C3N4 could be mainly attributed to the doping-induced electronic redistribution and structural reconstruction.

Nanorod-like Zn2GeO4 and diverse Zn2GeO4:xEu nanostructures were controllably synthesized via a surfactant-free hydrothermal route. Detailed composition and morphology were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM). The influence of Eu3+-doping on the phase and size transition of Zn2GeO4 nanocrystals was investigated, and a possible Zn2GeO4:xEu crystal growth mechanism, which is ascribed to hetero-valence ion doping, is proposed. Photoluminescence (PL) spectra indicate that Zn2GeO4:xEu phosphors give both the bluish-white emission from the Zn2GeO4 host and orange-red emission of Eu3+ ions. The morphologies of calcined Zn2GeO4:xEu were studied and their PL properties were also investigated. The results suggested that the emission of both the Zn2GeO4 host and Eu3+ ions can be adjusted via tuning the concentration of Eu3+-doping, excitation wavelengths and calcination schedules of the Zn2GeO4:xEu nanocrystals. Therefore, Zn2GeO4:Eu nanocrystals with multi-color as well as white light emission displayed a potential application for white light-emitting diodes.

Non-agglomerated and uniform Eu3+-doped NaGdF4 nanocrystals were synthesized via a facile one-step precipitation method at room temperature. Under pulsed magnetic fields, the luminescence properties of the as-prepared samples have been recorded and discussed in detail. Particularly, “controllable eliminating luminescence” of 5D0–7F0 transition in Eu3+ was achieved during the magneto-optical interaction. Magnetic field assisted cross-relaxation of excited electrons was derived from Zeeman splitting of the higher 5D energy level, and the magnetic confinement of f electron wave functions was proposed which were responsible for the change in luminescence intensity with a variation of magnetic field strength. The characteristic variation of the emission band under pulsed magnetic fields promises an optical probe for magnetic field detection.

By finely tuning the electrospun parameters (feeding rate of solution, working voltage and distance, etc.) and concentration of inorganic salts, various ZnAl2O4 nanostructures (nanoparticles, nanonecklaces, nanofibers, nanotubes and hollow micromelts) were controllably synthesized by a single-nozzle electrospinning technique. The formation mechanisms of different ZnAl2O4 nanostructures, including ‘oriented attachment’ mechanism, ‘gas-push’ mechanism, etc., were proposed to elucidate the morphology of the nanostructures and microstructure evolvement process. The morphology and microstructure of calcined electrospun nanostructures were considered to be mainly dependent on two factors, i.e. concentration of inorganic salts and size of as-prepared electrospun nanofibers. Using Ni2+ ions as activators, broadband near infrared (NIR) emission covering 1000–1400 nm peaking at about 1176 nm was detected in Ni2+-doped ZnAl2O4 nanostructures. The broadband NIR emission at around 1.3 μm optical communication window with a long lifetime of ∼640 μs makes Ni2+-doped ZnAl2O4 nanostructures as a promising candidate for micro/nano-broadband optical amplifiers, fibers, etc.

We synthesized NaNbO3 micro/nano-crystals with six morphologies and three different crystal structures using the hydrothermal method. Each single hexagonal NaNbO3 micro/nano-crystal (samples No. 1–3) exhibited a strong second-order nonlinear response. By calculating the average intensity and measuring the polarization response of each of these hexagonal crystals (samples No. 1–3), it was demonstrated that the same crystal structure displays a similar optical second harmonic generation (SHG) response. Furthermore, SHG was shown to be independent of the morphology and identical for similar crystals, which is expected for a volume effect with a second-order susceptibility tensor depending on the properties of the material. The optical SHG properties of these NaNbO3 micro/nano-crystals together with the previous related research suggest that these non-toxic crystals may find promising applications in biological imaging and related fields.

We demonstrated remarkably enhanced 2.7 μm emission in glass-ceramic (GC) fibers containing NaYF4:Er3+ nanocrystals with 980 nm excitation for the first time. The melt-in-tube technique is of scientific and technical significance for the fabrication of GC fibers in comparison to the conventional rod-in-tube technique. The obtained precursor fibers, in which the structure can be maintained well, exhibit no obvious element diffusion or crystallization during the fiber-drawing process. After a careful heat treatment, NaYF4 nanocrystals were controllably precipitated in the glass fiber core. Owing to the incorporation of Er3+ ions into the low phonon energy NaYF4 nanocrystals, enhanced 2.7 μm emission was achieved from the Er3+-doped GC fibers, which was almost undetectable in precursor fibers due to the high phonon energy of the borosilicate glass fiber matrix. Moreover, the 2.7 μm emission lifetime was obtained due to the excellent emission properties of Er3+ in the GC fibers. The transmission loss values of precursor fibers and GC fibers at 1310 nm were measured to be 7.44 dB m−1 and 11.81 dB m−1, respectively. In addition, a theoretical simulation based on the rate equations and propagation equations was performed to evaluate the possibility of 2.7 μm laser output. The excellent optical properties endow the GC fibers with potential applications for mid-infrared fiber lasers.

Nonlinear optical (NLO) effects originating from materials doped with rare-earth ions possess colossal potential for application in all-optical switches. However, among previous studies, Er3+ ion-doped glass ceramics (GCs) with remarkable NLO features have been investigated with respect to optical modulation applications by tailoring their nonlinear transmittance upon excitation at various near-infrared (NIR) wavelengths, which might prove to be a simple way of achieving “on–off” optical modulation in future all-optical switches. Here, we present the first observation of tailorable nonlinear transmittance in germanate oxyfluoride GCs containing Er3+:LaF3 nanocrystals, manipulated by excitation at 808, 980, and 1550 nm, which is consistent with the results from theoretical calculations and simulations. Furthermore, we conduct experimental investigation and analysis related to energy level transitions and dynamical evolution, indicating that these intriguing NLO features can be attributed to the differentiation between excited state absorption accompanied by up-conversion luminescence and stimulated emission processes during excitation at discrepant NIR wavelengths. Importantly, bidirectional optical switching for the “on–off” toggle effect has been successfully demonstrated by selectively tailoring the nonlinear transmittance of the single Er3+-doped GCs. This tailorable NLO behavior of Er3+-doped GCs, which is dependent on excitation at different NIR wavelengths, might provide a versatile strategy for the development of next-generation bidirectional all-optical switches.

The direct and effective synthesis of PbS quantum dots (QDs) in a solid-state matrix is of great importance in the production and application of PbS QDs photonic devices. The present article describes the direct precipitation of PbS QDs in an inorganic glass matrix by the irradiation of a femtosecond (fs) laser. It has been demonstrated that the formation of the QDs is strongly influenced by the thermal effect of the fs laser. The effect of the irradiation parameters and of Ag clusters on the precipitation of QDs has been investigated, in addition to the spatial distribution of the QDs in the irradiated area, and a mechanism is suggested. The confocal Raman spectra indicate that after irradiation the concentration of the QDs is the highest at the center. On the other hand, heat treatment of the irradiated sample has also been carried out to adjust the size, distribution and photoluminescence of QDs within the glass matrix. The electron probe microanalyzer (EPMA) has provided direct evidence for the large change in refractive index and for the ring-shaped structure formed on irradiation. Based on selective local control of the PbS QDs, a waveguide demonstration has been conducted to illustrate the feasibility of directly writing a PbS QDs waveguide with an fs laser in a glass matrix.