Search

In recent years, there has been much interest in inorganic perovskite nanocrystals (NCs) because of their extensive tunability over the visible range, high quantum yield (QY), and photoluminescence (PL). Inorganic perovskite was considered to be the photoactive material for photovoltaic cells because of its excellent photoelectric qualities. The next generation of high-performance solar cells was thought to benefit most from all-inorganic perovskite due to its long electron–hole diffusion length, high carrier mobility, and broad absorption spectrum. In this paper, femtosecond (fs) laser direct writing technology was used to accomplish spatially selective crystallization of CsPbBrxCl3−x (x = 0–3) NCs in precursor glass. By modifying the laser parameters, the size of the precipitated NCs could be regulated, and the photoluminescence of the NCs could be adjusted from blue to green. The optical properties and morphology of the NCs were analyzed by PL spectra and transmission electron microscopy (TEM). Based on fs laser-induced local crystallization, a linear array-based solar concentrator was processed in CsPbBrxCl3−x (x = 0–3) precursor glass and showed higher photoelectric conversion efficiency than that with the bulk glass sample. [ABSTRACT FROM AUTHOR]

Bismuth (Bi)-doped glasses with broadband near-infrared (NIR) emission have been drawing increasing interest due to their potential applications in tunable fiber lasers and broadband optical amplifiers. Yet, the realization of highly efficient and ultra-broadband Bi NIR emission covering the whole telecommunication window remains a daunting challenge. Here, via rationally controlling the content of Al2O3 to control the local environment and structural defect states around the Bi NIR active centers (BACs), various luminescence centers can coexist stably in a glass matrix. Consequently, tunable ultra-broadband multi-band NIR emission with four emission bands at ∼924, ∼1154, ∼1265, and ∼1516 nm was achieved in a Bi-doped germanate glass under single wavelength excitation. More importantly, such ultra-broadband multi-band Bi NIR emission with excellent thermal stability can be well retained after the glass was drawn into an optical fiber by a rod-in-tube method. The fibers show an obvious broadband ASE spectrum spanning a range of 1000–1600 nm. This work is helpful for understanding the mechanism of Bi NIR emission and offers a simple and feasible method for developing novel photonic devices with ultra-broadband Bi NIR emission. [ABSTRACT FROM AUTHOR]

Ultraviolet-C (UVC) photons have the potential to be used in a broad spectrum of fields, like sterilization and tagging. However, there is little natural UVC component on the Earth's surface due to the absorption of sunlight by the ozone layer, thus making exploitation of artificial UVC light a meaningful issue. This study introduces a strategy for generating UVC emission via an upconversion mechanism from Pr3+-doped SrSiO3 upon irradiation of visible light. The excitation sources include the commonly used blue laser diode (LD) emitting at 450 nm, as well as sunlight. The dependence of UVC intensity on the power density of 450 nm LD indicates that the UVC emission stems from a two-photon upconversion process. The UVC photons from the as-prepared Pr3+-doped SrSiO3 are then used for high signal-to-noise ratio and even background-free tagging in several complex scenarios and also for sterilization. In one word, our work enriches the upconversion luminescent materials emitting in the UVC wavelength range and demonstrates the potential applications of upconverted UVC photons, including tagging and sterilization. [ABSTRACT FROM AUTHOR]

The rapid development of near-infrared (NIR) spectroscopic techniques has greatly facilitated the exploration of novel broadband NIR-emitting materials as advanced smart NIR light sources. However, the pursuit of high-efficiency and excellent thermal stability photonic materials with broadband NIR emission, especially in the NIR-II region, is still unsatisfactory. Herein, we report the design of a thermally stable Bi-doped germanate glass with tunable broadband NIR emission varying from the NIR-I (850–1050 nm) to NIR-II (850–1500 nm) region upon blue light excitation. The NIR emission peaks varied from 946 to 1142 nm due to conversion in the highly environmentally sensitive Bi NIR active centers, and their emission intensity and lifetimes were >84% at 150 °C due to high structural rigidity and the weak electron–phonon coupling effect. The NIR glass-converted-LEDs generated an output power of 53.2 mW (NIR-LED-I) and 179.5 mW (NIR-LED-II), respectively (at a current of 320 mA). The night vision, bio-imaging, and food quality analysis were also demonstrated, suggesting that Bi-doped glass has great application potential in novel smart compact NIR light sources. [ABSTRACT FROM AUTHOR]

The valence state conversion of lanthanide ions induced by femtosecond laser fields has attracted considerable attention due to their potential applications in areas like high-density optical storage. However, the physical mechanisms involved in valence state conversions still remain unclear. Here, we report the first experimental study of controlling the reduction of trivalent samarium ions to divalent ones in sodium aluminoborate glass by varying the polarization status of the 800 nm femtosecond laser field. As the laser field is varied from linear to circular polarization, the reduction efficiency can be greatly decreased by about fifty percent. This polarization-dependent reduction behavior is found to directly correlate with the nonresonant two-photon 4f–4f absorption probability of the trivalent samarium ions in both experiment and theory. Multiphoton excited charge transfer between oxygen and samarium is considered to be responsible for the photoreduction. Our work demonstrates a controllable and effective way in tuning the valence state conversion efficiency and sheds light on the underlying mechanisms. [ABSTRACT FROM AUTHOR]

Temperature measurement based on thermally dependent emissions from intra-configurational 4f–4f transitions of rare earth ions has been developed as an efficient method for non-contact thermometry, but it remains challenging for high resolution temperature measurement due to the inherent limitation of the energy gap (200–2000 cm−1) between the thermally coupled energy levels (TCELs). In this work, a group of oxide phosphors, Y2O3:xEr3+, yLi+, prepared by a low-temperature combustion method (LCM) were developed for dual-mode optical thermometry by leveraging the temperature-responsive upconversion (UC) emission from Er3+ ions. We discover that the introduction of the dopant (Li+ ion) into Y2O3: Er3+ synthesized by the LCM can significantly regulate the original crystal configuration and its surface structure. Its transition to a monocrystalline state can solve the problem of high impurity defects and possible high dislocation density that cannot be overcome by a polycrystalline state, thus remarkably increasing the emission intensity of UC (about 28 times). In addition, the dual-mode optical thermometry based on thermally coupled energy levels (TCELs) and non-thermally coupled energy levels (NTCELs) was examined with respect to the different temperature dependence of the three characteristic emission peaks of the Er3+ ions (i.e., from excited levels of 2H11/2, 4S3/2 and 4F9/2). At temperatures from 123 to 443 K, the maximum relative sensitivities (SRmax) are 6.67% K−1 and 1.13% K−1 and the maximum absolute sensitivity (SAmax) reaches 0.42% K−1and 2.48% K−1, respectively. The excellent sensitivity at low temperatures indicates that our results not only provide an effective doping strategy for improving the crystal type character and surface structure of oxide phosphors, but also provide an effective guideline for the low temperature environmental applications of functional upconversion optical thermometers. [ABSTRACT FROM AUTHOR]

Oxy-fluoride nano-crystallized glass-ceramics (NGCs), with integrated advantages of amorphous glasses and fluoride crystals, show great potential for applications in lighting, information storage and lasers. However, the photoluminescence quantum yields (PLQYs) of traditional NGCs are restricted by the difficulty in the incorporation of the number of active ions into crystal structures due to the mismatch of the radius in the ionic substitution process. Herein, an in situ dopant-induced nano-crystallization strategy is proposed for the design and fabrication of NGCs with high PLQY. The strategy is suitable the precipitation of all kinds of rare-earth-fluoride nanocrystals in glasses and thus dramatically enhances the PL efficiency in upconversion and down-shifting emission. The upconversion PLQY of designed NGCs (2.77%) is 3 times larger than that of well-established NGC containing β-NaYF4 crystals (0.78%), which have widely been considered the most efficient NGC for upconversion luminescence. Moreover, the designed NGCs also exhibit higher optical transmittance and PL behaviors show more excellent photo-thermal stability, in comparison with that of traditional NGCs. Most importantly, low-threshold, high-slope-efficiency microsphere lasers have been successfully demonstrated by leveraging our well-designed NGCs. This strategy opens a new avenue for the design and fabrication of highly efficient optical gain micro-/nanomaterials for applications in emerging photonics devices. [ABSTRACT FROM AUTHOR]

All inorganic metal halide perovskite quantum dots (QDs) exhibit excellent optical properties promising for diverse applications, while their inherent frangibility remains an enormous challenge for both scientific research and practical applications. Recently emerged oxide glasses doped with such QDs exhibit high stability against degradation and are thus highly promising for photonic applications. Here, we demonstrate the tuning of the linear and nonlinear optical properties of perovskite QD-doped glass through modulation of its network topology. By introducing a metal fluoride network modifier, we show that the precipitation of the QDs can be promoted as a result of the enhanced ion mobility during heat treatment. The QD-doped glasses show strong one-photon and two-photon upconversion photoluminescence (PL). Also, the PL intensity can be enhanced by up to 800% for the sample with an optimal local structure. In addition, the control of QD precipitation by modulating the glass network topology could allow for the observation of a cross-over from saturable absorption to reverse saturable absorption. The methodology for tuning the optical properties of QD-in-glass composites studied here might be applied for the design of photonic glasses for relevant applications. [ABSTRACT FROM AUTHOR]

With the wide use of micro–nano photonic devices in on-chip optical communication, physical and chemical sensing, organic microlasers have gained increasing attention owing to their special advantages including high integration, easy preparation and excellent optical properties. However, traditional microlasers suffer from the "aggregation-caused quenching" (ACQ) effect of gain molecules and high lasing thresholds. In this contribution, we meticulously designed organic microlaser assemblies based on an "aggregation-induced emission" (AIE) fluorophore for its unique characteristics. An innovative AIE fluorophore, namely triphenylamine-benzo[1,2-b:4,5-b′]-dithiophene 1,1,5,5-tetraoxide (TPA-BDTO), with highly efficient emission at the aggregated state is employed to hybridize with the PMMA matrix, obtaining microbottles with an ultra-smooth surface via the self-assembled strategy. Benefiting from the spatially well-separated intensity based on the prolate shape of the TPA-BDTO–PMMA microbottle, we realize a single-mode microlaser in a microbottle with an appropriate pump power via precise manipulation. Moreover, the TPA-BDTO–PMMA microlaser is demonstrated as an axial tensile strain sensor with high sensitivity (0.34 pm με−1), high resolution, real-time response and simple structure, which create new opportunities for organic microlasers and even lay a foundation for the research of lab-on-chips. [ABSTRACT FROM AUTHOR]

The pursuit of efficient light sources has stimulated continued effort in the search of materials and methods for generating white light emission. In addition to the white light produced by light-emitting diodes (LEDs) and fluorescent lamps that involves spectral conversion of high energy to low energy emission, recent studies showed that it was also possible to produce white visible light by irradiating different active materials with near-infrared (NIR) constant-wave (CW) lasers. In this review, we begin by introducing and categorizing different materials that exhibit NIR laser driven white light emission, including normal inorganic phosphors, organometallic compounds, graphene, etc. We then discuss the photophysical behavior of this process in terms of optical spectra, temperature evolution and photoelectric response. Different mechanisms of while light generation are analyzed afterwards, and the possibility of a more general physical picture of this process is discussed. This review is concluded with a summary of the current understanding and discussion on potential applications and future perspectives. [ABSTRACT FROM AUTHOR]

Fiber lasers, especially single-frequency fiber lasers, are highly desirable due to their long coherent length and narrow spectral linewidth that are unattainable in common photonic devices. However, significant challenges in the fabrication of high quality fiber laser devices still exist. In this paper, fibers with 1.55 μm laser output have been achieved using Er3+/Yb3+-codoped glass-ceramic (GC) as a core material and a “molten core” fiber-drawing technique. The prepared GC fibers demonstrate enhanced laser output with an optical signal-to-noise ratio of 65 dB and a slope efficiency of 11.8%, which are higher than those of the as-prepared glass fiber. Furthermore, a single-longitudinal mode laser with a linewidth of 7.4 kHz and a relative intensity noise (RIN) of −148.8 dB/Hz is achieved, manifesting the potential applications of the GC fibers in optoelectronic fields. Theoretical calculations and simulations are employed to understand the relation between the optical performance of the fiber laser and the atomic structure in the phase-separated region of the oxyfluoride glass cores. The demonstrated GC fibers provide a new platform for the development of multifunctional fiber lasers and open a new avenue towards practical applications for crystallized fibers. [ABSTRACT FROM AUTHOR]

Thermal quenching is quite usual in different luminescent materials due to enhanced phonon population, while anti-thermal quenching or thermally enhanced luminescence does exist in a few systems, which is intrinsically associated with the presence of thermally coupled energy levels or a phase transition. However, we show here that an extrinsic effect involving volatilization of surface moieties contributes to switchable enhancement of upconversion (UC) at elevated temperatures. We observe this abnormal thermally enhanced UC behavior in a typical UC system, NaGdF4:Yb,Tm nanoparticles, which are coated with moieties that are unstable at elevated temperatures. Unlike low-temperature UC behavior, this thermally enhanced emission process is not completely reversible during several heating–cooling cycles, and the volatilization/condensation of environmental moieties on the particle surfaces contributes to the reversible enhancement of the UC emission at elevated temperatures. Combined with numerical simulation, we clarify that the phonon-assisted nonradiative decay rates are greatly suppressed at high temperatures due to the volatilization of the adsorbed moieties, leading to the enhancement of the UC quantum efficiency. By deliberately blocking the surface processes, the thermally enhanced UC emission disappears completely and the thermal quenching process re-appears as usual. [ABSTRACT FROM AUTHOR]

NaGdF4 is considered to be one of the efficient hosts for up-conversion (UC) materials; in particular, rare earth-doped hexagonal-phase NaGdF4 exhibits strong upconversion luminescence. However, thin films of NaGdF4 are difficult to prepare by conventional methods due to the presence of fluorine, and hexagonal-phase NaGdF4 cannot be obtained easily at low temperatures. Herein, a thin film of hexagonal-phase NaGdF4:Yb–Er is fabricated by electro-deposition at moderate temperatures. More importantly, the phase of NaGdF4:Yb–Er thin film can be controlled to enhance upconversion luminescence by adding polyvinylpyrrolidone (PVP) in the electrolyte. Upon excitation using a 980 nm diode laser, the UC emission intensity of hexagonal thin films increases significantly compared with that of cubic films. The results pave a new way to control the phase of fluoride crystal films that may find potential applications in photovoltaic devices. [ABSTRACT FROM AUTHOR]

Organic semiconductors, such as polycyclic aromatic hydrocarbons, are typically not responsive to near infrared (NIR) light due to their relatively large bandgaps. Here, we show that the NIR light at 980 nm can be efficiently converted to broadband visible upconversion (UC) emission by rubrene molecules in a solution dispersed with upconversion nanoparticles (UCNPs). Spectroscopic characterizations indicate that the sensitization of emission by rubrene molecules strongly depends on the location of the 4f levels of Er3+ ions and the interplay between reabsorption and Förster-type energy transfer. Even for the solution with the highest rubrene concentration (＞1 mg mL−1), energy transfer by reabsorption of UC emission from the UCNPs is the dominant process, and the radiationless resonant energy transfer process is weak, as the separation between most rubrene molecules and NCs is far larger than the Förster distance. The results of this work could be of particular interest for the development of organic–inorganic hybrid systems for NIR light harvesting and detection. [ABSTRACT FROM AUTHOR]

Novel nanocomposite glass ceramics (GCs), containing bi-functional NaYF4:Yb3+/RE3+(RE3+ = Er3+, Nd3+) and NaAlSiO4:Cr3+ nanocrystals, were synthesized by a melt-quenching process and subsequent heat-treatment. XRD and TEM results indicate that two types of nanocrystals, NaYF4 and NaAlSiO4, disperse homogeneously in the glass matrix. Photoluminescence (PL) spectra and lifetime measurements demonstrate that RE3+ and Cr3+ ions selectively enter into the precipitated NaYF4 and NaAlSiO4 nanocrystals, respectively, after crystallization, which restrains the potential energy transfer (ET) between the rare earth (RE) and transition metal (TM) ions. Significantly, there are three modes to carry out the optical thermometry based on the fluorescence intensity ratio (FIR) from two thermally coupled levels of Nd3+, the FIR from the Cr–Nd non-thermally coupled system and the fluorescence lifetime of Cr3+. Compared to standard temperature sensors based on a single mode technique, the Yb3+/Nd3+/Cr3+ codoped oxyfluoride GCs, with excellent sensitivity and high precision, open up a new path in the optical thermometry field. [ABSTRACT FROM AUTHOR]

White light generation is of particular interest for artificial lighting as well as spectroscopy. Here, we report the conversion of constant-wave (CW) near infrared (NIR) laser to continuum white light emission by Yb-doped oxides. The white light generation occurs by irradiating the oxide powders with the NIR laser at room temperature and atmospheric pressure. The excitation powder dependence of the emission intensity demonstrates an evident threshold, above which the brightness increases abruptly. By using an infrared thermal camera, it is found that the above-threshold rise of emission intensity is accompanied by the rapid rise of sample temperature, and the lowest temperature of white light emission is about 630 °C, which is far lower than the spectrally derived blackbody radiation temperature (＞2000 °C). In addition, the results show that the peak of the emission is close to the excitation laser wavelength (940 nm), and the spectral width grows with excitation power and sample temperature. These observations lead us to conclude that the white light is associated with the thermally enhanced spectral continuum generated by nonlinear optical processes, such as resonant Raman scattering. [ABSTRACT FROM AUTHOR]

One-dimensional nanomaterials usually possess unique anisotropic chemical or physical properties. For practical device applications, one of the biggest challenges is their large-scale assembly with predesigned architecture to render optimized collective properties. Based on our previous studies, here we report an extended investigation on the macroscopically aligned assembly of gold nanorods with tunable aspect ratio (AR) in transparent polymer films based on the electrospinning technique. The optical properties of the composite films were investigated using polarized extinction spectra and the Z-scan technique. Due to the collective longitudinal LSPR of the macroscopically aligned gold nanorods, the transparent composite films exhibited anisotropically enhanced optical nonlinearity. The intensity of the nonlinear optical signal of the films can be tuned by varying the polarization direction of the laser on the films. Moreover, the influence from the AR and the doping concentration of GNRs on the optical properties of the composite films was also investigated. To demonstrate an example of practical applications, the composite film was employed as a saturable absorber to construct a pulsed fiber laser. Inspiringly, the pulsed fiber laser with switchable mode-locking and Q-switching operation modes was realized successfully. The switching of the operation mode of the laser can be triggered simply through variation of the laser's polarization direction. Such a pulse-width tunable fiber laser is potentially useful in various application scenarios. [ABSTRACT FROM AUTHOR]

We report the fabrication of Eu-doped CaF2 films with an adjustable oxidation state of Eu ions such as Eu2+, Eu2+/Eu3+ or Eu3+ by the electro-deposition method, which are promising for luminescence converters for LEDs. Usually, the Eu2+ ion is unstable and can be very easily oxidized into the Eu3+ ion in solution. We reduced Eu3+ ions into Eu2+ ions by the electrochemical reduction method, and then incorporated Eu2+ ions into a CaF2 film during successive electro-deposition. We controlled the balance between Eu2+, Eu2+/Eu3+ and Eu3+ doped in the CaF2 thin film by regulating the parameters of the deposition solution (pH). More importantly, we controlled the luminescence from the Eu doped CaF2 film to generate pure blue luminescence, white luminescence, and red luminescence. These results not only provide a method for reducing Eu3+ ions into Eu2+ ions in solution, but also establish a new preparation technique for Eu2+/Eu3+ ion doped films and pave a new way for potential applications of Eu2+ doped luminescent materials. [ABSTRACT FROM AUTHOR]

Classic optical glass for mirror and lens systems may benefit from distinctive features of the glass state such as chemical and structural homogeneity at large length scales. However, this has restricted the ability of these systems for local light management. Herein, we have presented a multiscale strategy for glass design and experimentally realized a new multiscale structured glass through relaxation control. The constructed material is characterized by rich microstructures spanning the nano- (down to ∼50 nm) and micrometer scales (up to ∼70 μm), demonstrating a previously unrealized optical behavior. These materials combine excellent optical transparency and internal scattering. Importantly, their unique multiscale configuration enables simultaneous control of the chemical state and local chemical environment of the incorporated dopant. This allows us to generate color-switchable emission (blue, red to white) with high brightness and build a colorimetric temperature sensor. Our results highlight that the multiscale design strategy may provide opportunities for the development of a new generation of photonic glass. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report optical depletion of upconversion luminescence (UCL) in NaYF4:Yb3+,Tm3+ nanoparticles excited simultaneously by 980 nm and 1550 nm lasers. The UCL intensity is greatly depleted, while the downshifted emission at 1210 nm is obviously enhanced. The disturbances of 1550 nm photons on energy transfer between Yb3+ and Tm3+, cross relaxation (CR), the thermal effect and the stimulated emission depletion (STED) process are qualitatively evaluated. Our investigations verify that the unexpected depletion phenomena are governed by the STED process. The power densities of the 980 nm and 1550 nm lasers are both less than 100 W cm−2, which will greatly reduce the thermal effect and damage and extend the applications of such nanomaterials. These results provide keen insights into controlling emission colors in optical processes, and offer potential applications in multicolor displays and STED nanoscopy. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A thorough understanding of energy transfer and upconversion (UC) processes between trivalent lanthanide (Ln3+) ions is essential and important for improving UC performance. However, because of the abundant energy states of Ln3+ ions, UC mechanisms are very complicated, which makes it a challenge to exclusively verify and quantitatively evaluate the dominant process. In this study, the fundamental excitation processes of Tm3+-doped NaYF4 nanocrystals under 800 nm continuous wave (CW) laser excitation were experimentally investigated on the basis of the quantum transition principle. An 800 nm CW laser combined with other wavelength CW lasers, including 471 nm, 657 nm, 980 nm, and 1550 nm lasers, were designed to study in-depth the excitation processes of UC luminescence via simultaneous two-wavelength laser excitation. The results indicate that the excited state absorption of 3H6→3H4∼∼3H5→1G4 is the dominant pathway of the 481 nm and 651 nm emission bands, and two kinds of energy transfer UC pathways, uniformly expressed as 1G4 + 3H4→1D2 + 3F4, play the primary roles in the 456 nm emission band. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Owing to the unique mechanism of photoelectron storage and release, long persistent phosphorescence, also called long persistent luminescence or long lasting afterglow/phosphorescence, plays a pivotal role in the areas of spectroscopy, photochemistry, photonics and materials science. In recent years, more research has focused on the manipulation of the morphology, operational wavebands and persistent duration of long persistent phosphors (LPPs). These desired achievements stimulated the growing interest in designing bio-labels, photocatalysts, optical sensors, detectors and photonic devices. In this review, we present multidisciplinary research on synthetic methods, afterglow mechanisms, characterization techniques, materials system, and applications of LPPs. First, we introduce the recent developments in LPPs for the synthesis of nanoparticles from the aspects of particle sizes, monodispersity and homogeneity based on the urgent application of bio-imaging. In the later sections, we present the possible mechanisms, which involve the variation of trap distribution during the trapping and de-trapping process, complicated photo-ionization reaction of trap site levels and impurity centers together with their corresponding migration kinetics of carriers. Meanwhile, we emphasize the characterization techniques of defects, used to qualitatively or quantitatively describe the types, concentrations and depths of the traps. This review article also highlights the recent advances in suggested LPPs materials with a focus on the LPPs' hosts and optically active centers as well as their control, tuning and intrinsic links. We further discuss the classification of LPPs based on the different emission and excitation wavebands from the ultraviolet to the near-infrared region along with an overview of the activation mode of afterglow. Afterwards, we provide an exhibition of new products towards diverse application fields, including solar energy utilization, bio-imaging, diagnosis, and photocatalysts. Finally, we summarize the current achievements, discuss the problems and provide suggestions for potential future directions in the aforementioned parts. [ABSTRACT FROM AUTHOR]

Nanofibers are characterized with unique electronic, magnetic and optical properties, due to their extremely high aspect ratio and large specific surface area. Assembly of nanofibers with predesigned macro architectures is a key step toward practical applications. Herein, we demonstrate the scalable oriented assembly of nanofibers based on electrospinning, and explore their potential application in constructing optically anisotropic films. By the post soaking-and-drying approach, the nonwoven films assembled by oriented polymer nanofibers can be readily converted to flexible films with high transparency, which show optical transmission contrast exceeding 0.9 in the visible to near infrared region. The method for preparation of optically anisotropic films proposed here circumvents the sophisticated dye-doping and thermal drawing processes which are inevitable in conventional approaches. Considering the scalability potential of the electrospinning technique, the method demonstrated here is promising for industrial production of film polarizers. [ABSTRACT FROM AUTHOR]

Transfer of energy occurs endlessly in our universe by means of radiation. Compared to energy transfer (ET) in free space, in solid state materials the transfer of energy occurs in a rather confined manner, which is usually mediated by real or virtual particles, including not only photons, but also electrons, phonons, and excitons. In the present review, we discuss the recent advances in optical ET by resonance mediated with photons in solid materials as well as their nanoscale counterparts, with focus on the photoluminescence behavior pertaining to ET between optically active centers, such as rare earth (RE) ions. This review begins with a brief discussion on the classification of optical ET together with an overview of the theoretical formulations and experimental method for the examination of ET. We will then present a comprehensive discussion on the ET in practical systems in which normal photoluminescence, upconversion and quantum cutting resulted from ET involving metal ions, QDs, organic species, 2D materials and plasmonic nanostructures. Diverse ET systems are therefore simply categorized into cases of ion–ion interactions and non-ion interactions. Special attention has been paid to the progress in the manipulation of spatially confined ET in nanostructured systems including core–shell structures, as well as the ET in multiple exciton generation found in QDs and organic molecules, which behave quite similarly to resonance ET between metal ion centers. Afterwards, we will discuss the broad spectrum of applications of ET in the aforementioned systems, including solid state lighting, solar energy utilization, bio-imaging and diagnosis, and sensing. In the closing part, along with a short summary, we discuss further research focus regarding the problems and possible future directions of optical ET in solids. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]