Upconversion Photoluminescence Research Articles

Synthesis and up-conversion luminescence of Er3+ and Yb3+ co-doped La14W8O45 phosphors

Pure phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 up-conversion luminescent materials were successfully prepared by the hydrothermal method combined with calcination treatment. The structures, morphology, and optical properties of the samples were analyzed by X-ray powder diffractometer (XRD), scanning electron microscope (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), and up-conversion photoluminescence spectroscopy (UPL) with a 980 nm laser. XRD results indicated that the obtained samples are single-phase orthorhombic Er3+ and Yb3+ co-doped La14W8O45 crystals. SEM results showed that the prepared sample exhibits an irregular and melted polyhedral-like morphology with agglomeration in submicron size of particles approximately 50–200 nm. UV–vis DRS results revealed that the La14W8O45 crystal is a direct semiconductor with an optical band gap of 3.84 eV. The prepared Er3+ and Yb3+ co-doped La14W8O45 crystals exhibit strong up-conversion emission peaks at about 526 nm, 548 nm, and 660 nm under 980 nm laser excitation. The intensity of up-conversion luminescence is affected by the Er3+ doping concentration, and concentration quenching will be observed due to the cross-relaxation (CR) process when the Er3+ doping content is above 1%. The pumping power dependence of the luminescence indicated that the up-conversion emissions of samples are excited by a two-photon absorption process. The color coordinates of the samples are located in the green light region.

Enhanced piezoelectricity and non-contact optical temperature sensing performance in Er3+ ion modified (K,Na)NbO3-based multifunctional ceramics

Rare earth ions doped ferroelectrics have attracted wide attentions due to their multifunction characteristics with both ferroelectric/piezoelectric properties and intriguing photoluminescence performance, which show great prospects for future multifunctional devices. In this work, a novel rare earth Er3+ ion modified potassium-sodium niobate (KNN) based ceramics were elaborately designed and prepared by the conventional solid-state reaction. The microstructure, phase structure, electric properties and photoluminescence performance of the Er3+ ion modified KNN-based ceramics were systematically investigated. Enhanced piezoelectricity (a considerable d33 of exceeding 300 pC/N and a large d33* up to 500 p.m./V) was realized through optimizing the substitution of BaZrO3 by (Er0.5,Na0.5)ZrO3. Both down-conversion and up-conversion photoluminescence emissions were detected in the optimal composition. The temperature-dependent upconversion emissions of the optimal Er3+ modified ceramic sample in the temperature range of 303–573K were verified to be applicable for non-contact optical temperature sensing with a maximum sensitivity Sa of 0.0028 K-1 and a peak relative sensitivity Sr of 0.96% K−1. Moreover, low-temperature sensing performance with a maximum Sr of 16.7% K−1 in the temperature range of 80–280K was also presented based on the temperature-dependent down-conversion emissions. With both decent electrical properties and intriguing photoluminescence performance, the Er3+-modified KNN-based ferroelectrics exhibit good application potential in the future multifunctional optoelectronic devices.

Новые апконверсионные объемные и нанолюминофоры на основе Sr-=SUB=-2-=/SUB=-Y-=SUB=-8-x-y-=/SUB=-Yb-=SUB=-y-=/SUB=-Tm-=SUB=-x-=/SUB=-Si-=SUB=-6-=/SUB=-O-=SUB=-26-=/SUB=-

Polycrystalline phosphors with a Sr2Y8-x-yYbyTmxSi6O26 (x=0.005-0.5, y=0.2,0.3) total formula were synthesized. Nanoluminophor has been obtained from the Sr2Y7.695Yb0.3Tm0.005Si6O26 microcrystalline sample by the vacuum electron been evaporation, in the amorphous state, with the ~10.6 nm particle size. It is found, raman spectra undergoing modification by the transition from bulk- to nanosize state. Photoluminescene spectra micro- and nanophosphors are studied. Intensity of the blue emission, by the UV ligth excitation, grows in the x=0.005-0.02 region, with the x increasing. Upconversion photoluminescence (UPCL) spectra of the bulk phosphors and nanosample based on the Sr2Y7.695Yb0.3Tm0.005Si6O26 were measurd. At the pumping power around 70.8 mW, by the laser source with the λ=980 nm, thereshold population of the 3F3 level of Tm3+ ions exist. At a power higher 70.8 mW, a sharp increase of the luminescence intensityof the bulk- and nanophosphor occurs. For the 3H4->3H6 transition thereshold pumping power absent. This indicates that, pumping, during Yb->Tm energy transer, is a single photon process.

Enhancement of upconversion photoluminescence in phosphor nanoparticle thin films using metallic nanoantennas fabricated by colloidal lithography.

Lanthanide-doped upconversion nanoparticles (UCNPs), as multifunctional light sources, are finding utility in diverse applications ranging from biotechnology to light harvesting. However, the main challenge in realizing their full potential lies in achieving bright and efficient photon upconversion (UC). In this study, we present a novel approach to fabricate an array of gold nanoantennas arranged in a hexagonal lattice using a simple and inexpensive colloidal lithography technique, and demonstrate a significant enhancement of UC photoluminescence (UCPL) by up to 35-fold through plasmon-enhanced photoexcitation and emission. To elucidate the underlying physical mechanisms responsible for the observed UCPL enhancement, we provide a comprehensive theoretical and experimental characterization, including a detailed photophysical description and numerical simulations of the spatial electric field distribution. Our results shed light on the fundamental principles governing the enhanced UCNPs and pave the way for their potential applications in photonic devices.

Controlling the durability and optical properties of triplet-triplet annihilation upconversion nanocapsules.

Deep penetration of high energy photons by direct irradiation is often not feasible due to absorption and scattering losses, which are generally exacerbated as photon energy increases. Precise generation of high energy photons beneath a surface can circumvent these losses and significantly transform optically controlled processes like photocatalysis or 3D printing. Using triplet-triplet annihilation upconversion (TTA-UC), a nonlinear process, we can locally convert two transmissive low energy photons into one high energy photon. We recently demonstrated the use of nanocapsules for high energy photon generation at depth, with durability within a variety of chemical environments due to the formation of a dense, protective silica shell that prevents content leakage and nanocapsule aggregation. Here, we show the importance of the feed concentrations of the tetraethylorthosilicate (TEOS) monomer and the methoxy poly(ethyleneglycol) silane (PEG-silane) ligand used to synthesize these nanocapsules using spectroscopic and microscopy characterizations. At optimal TEOS and PEG-silane concentrations, minimal nanocapsule leakage can be obtained which maximizes UC photoluminescence. We also spectroscopically study the origin of inefficient upconversion from UCNCs made using sub-optimal conditions to probe how TEOS and PEG-silane concentrations impact the equilibrium between productive shell growth and side product formation, like amorphous silica. Furthermore, this optimized fabrication protocol can be applied to encapsulate multiple TTA-UC systems and other emissive dyes to generate anti-Stokes or Stokes shifted emission, respectively. These results show that simple synthetic controls can be tuned to obtain robust, well-dispersed, bright upconverting nanoparticles for subsequent integration in optically controlled technologies.

An overview on animal/human biomass-derived carbon dots for optical sensing and bioimaging applications.

Over the past decade, carbon dots (CDs) have emerged as some of the extremely popular carbon nanostructures for diverse applications. The advantages of sustainable CDs, characterized by their exceptional photoluminescence (PL), high water solubility/dispersibility, non-toxicity, and biocompatibility, substantiate their potential for a wide range of applications in sensing and biology. Moreover, nature offers plant- and animal-derived precursors for the sustainable synthesis of CDs and their doped variants. These sources are not only readily accessible, inexpensive, and renewable but are also environmentally benign green biomass. This review article presents in detail the production of sustainable CDs from various animal and human biomass through bottom-up synthetic methods, including hydrothermal, microwave, microwave-hydrothermal, and pyrolysis methods. The resulting CDs exhibit a uniform size distribution, possibility of heteroatom doping, surface passivation, and remarkable excitation wavelength-dependent/independent emission and up-conversion PL characteristics. Consequently, these CDs have been successfully utilized in multiple applications, such as bioimaging and the detection of various analytes, including heavy metal ions. Finally, a comprehensive assessment is presented, highlighting the prospects and challenges associated with animal/human biomass-derived CDs for multifaceted applications.

Phonon-Assisted Upconversion Photoluminescence of a Self-Trapped Exciton in the Rb2CuCl3 Single Crystal.

Phonon-assisted upconversion photoluminescence (UCPL) plays an important role in a wide range of fields such as optical refrigeration, sensitive optical thermometry, quantum state control, and upconversion optoelectronics. High photoluminescence quantum yield (PLQY) and strong electron-phonon coupling are two basic prerequisites of efficient UCPL materials. The self-trapped exciton (STE) system with the above-mentioned advantages hints that it may be a good candidate for phonon-assisted UCPL. Here, we synthesized Rb2CuCl3 single crystals (SCs) which yield a high PLQY of the STE emission at 400 nm, and an efficient phonon-assisted UCPL was demonstrated at room temperature. By exponentially fitting the intensity of temperature-dependent UCPL spectra, we obtained an optical thermometry sensitivity of SCs up to 6 mK at 295 K. We also propose that net cooling would be possible if the PLQY is improved up to 91.5% with 345 nm excitation. Our results open a new door to explore laser cooling in STE systems.

Comparison of Quantum Yield of Upconversion Nanocrystals Determined by Absolute and Relative Methods

Photoluminescence quantum yield (ϕ) is a key parameter of any luminescent material. There are two main ways to determine this value: 1) absolute, which requires calculation of the number of emitted and absorbed photons; and 2) relative, which utilizes the emission of a reference sample with known ϕ. Both methods become more complicated in case of upconversion (UC) photoluminescence, due to its nonlinear nature. The main obstacle to employing the relative method is the lack of a suitable reference with known UC quantum yield (UCQY, ϕ UC). Herein, a new UCQY reference material is presented, based on SrF2:1%Yb3+,1%Er3+ single crystal, for the relative measurement of ϕ UC for near‐infrared (976 nm)‐to‐visible UC. When utilizing this reference material, the ϕ UC is determined to be 2.5% (at 100 W cm−2) for α‐NaYF4:18%Yb3+,2%Er3+@CaF2 nanocrystals (NCs). This result coincides very well with the value for the same NCs determined using the absolute method of ϕ UC = 2.4% (at 100 W cm−2). The intensity dependence of UCQY yield for the NCs determined using the SrF2:1%Yb3+,1%Er3+ reference exhibits good agreement with the results acquired with the absolute method. In addition, various effects that can have an impact on the measured UCQY using absolute and relative methods are discussed.

Multiple anti-counterfeiting strategy by integrating up-conversion, down-shifting luminescence, phosphorescence and photochromism into NaYTiO4: Bi/Er phosphors

• The micron phosphors NaYTiO 4 : Bi/Er were prepared by solid state reaction. • NaYTiO 4 : Bi/Er phosphors possess considerable up-conversion, down-shifting luminescence, phosphorescence and photochromism performances. • A novel strategy for multiple anti-counterfeiting is proposed and successfully executed based on NaYTiO 4 : Bi/Er phosphors. • NaYTiO 4 : Bi/Er phosphors can be a great candidate for high-security-level anti-counterfeiting application. With the rapid development of science and technology, the high-security-level anti-counterfeiting technique is essential for ensuring property or information security. In this work, we prepared micron NaYTiO 4 : Bi/Er (NYT: Bi/Er) phosphors with integrating up-conversion (UC) photoluminescence, down-shifting (DS) emission, phosphorescence and photochromism (PC) performances for advanced multiple anti-counterfeiting application. Owing to the abundant energy levels of Er 3+ ions, the UC and DS luminescence behaviors are anticipated. Specifically, the yellow-green emission of Er 3+ ions can be observed upon 980 nm excitation, and the bright green emission is demonstrated under 281 or 254 nm excitation due to the energy transitions of Er 3+ ions and the energy transfer process from Bi 3+ to Er 3+ ions. Besides, the introduction of Bi 3+ ions generates defect levels in the matrix and thus leads to phosphorescence. Furthermore, the repeatable PC performance could be triggered by the 365 nm irradiation and vanished with 450 nm illumination or thermal stimulation. To verify the practical usability of NYT: Bi/Er phosphors on anti-counterfeiting applications, some experiments are designed and successfully executed. It is believed that the NYT: Bi/Er phosphors can be a promising candidate for high-security-level multiple anti-counterfeiting.

Unveiling room temperature upconversion photoluminescence in monolayer WSe2.

Upconversion photoluminescence (UPL) is a phenomenon describing an anti-Stokes process where the emitted photons have higher energy than the absorbed incident photons. Transition metal dichalcogenides (TMDCs) with strong photon-exciton interactions represent a fascinating platform for studying the anti-Stokes UPL process down to the monolayer thickness limit. Herein, we demonstrate room-temperature UPL emission in monolayer WSe2 with broadband near-infrared excitation. The measured excitation power dependence of UPL intensity at various upconversion energy gains unveils two distinguished upconversion mechanisms, including the one-photon involved multiphonon-assisted UPL process and the two-photon absorption (TPA) induced UPL process. In the phonon-assisted UPL regime, the observed exponential decay of UPL intensity with the increased energy gain is attributed to the decreased phonon population. Furthermore, valley polarization properties of UPL emission with circular polarization excitation is investigated. The demonstrated results will advance future photon upconversion applications based on monolayer TMDCs such as night vision, semiconductor laser cooling, and bioimaging.

Synthesis and Photocatalytic Applications of Functionalized Carbon Quantum Dots

Abstract Environmental degradation and energy shortages are becoming increasingly important as science and technology advance. Here, we review the photocatalytic approach of functionalized carbon quantum dots (CQDs) along with their up-converted photoluminescence behaviour, as well as their photoinduced electron transfer capabilities, opening a new path to effective metal-free photocatalyst. In this article, we are focusing on the recent invention of CQDs and CQD-based photocatalyst for environmental remediation such as dye degradation, CO2 conversion, and water splitting along with the categorization and synthesis of CQDs-derived photocatalysts, and applications for environmental concerns. Although it is essential to incorporate multiple perspectives, since CQDs and CQD-derived photocatalysts have varied perspectives to tackle unique environmental applications, our analysis is expected to offer additional details on CQD synthesis methods, tuning photocatalytic properties of CQDs with surface groups, and the mechanism of degradation of CQDs and CQD-based photocatalysts.

Magnetic and photoluminescence properties of rare-earth substituted quaternary spinel ferrite nanoparticles

Rare earth substituted quaternary spinel ferrites Ni0.5Zn0.5Fe1.95Eu0.05O4, Co0.5Zn0.5Fe1.95Dy0.05O4, and Cu0.5Zn0.5Fe1.95Tb0.05O4 were prepared by a low-temperature co-precipitation method without any post heat treatment. Structural confirmation of the prepared materials was done by XRD. Using TEM, their morphology was investigated. Magnetic studies were conducted using VSM. The prepared materials exhibit soft ferrimagnetic nature. The magnetization curves were further studied by applying the law of approach to saturation. Downconversion and upconversion photoluminescence properties of the prepared materials were investigated at different excitation wavelengths. No characteristic emission spectra of the rare-earths elements were observed. In the case of downconversion, a broad emission band formed by sub-bands and in the upconversion spectra, characteristic emission peaks were observed in all compositions. The observed emission spectra depict the presence of multiple energy levels within the band gap of spinel ferrites.

Energy Transfer from Pr3+ to Gd3+ and Upconversion Photoluminescence Properties of Y7O6F9:Pr3+, Gd3.

Upconversion materials have numerous potential applications in light energy utilization due to their unique optical properties. The use of visible light excitation to obtain ultraviolet emission is a promising technology with broad application prospects, while relevant research is absent. A series of Pr3+, Gd3+ doped Y7O6F9 phosphors were synthesized by traditional solid-state reaction. X-ray diffraction, scanning electronic microscopy, steady-state photoluminescence spectra, a decay dynamic, and upconversion emission spectra of the samples were studied. Under the excitation of 238 nm, the energy transfer from Pr3+ to Gd3+ was realized and a strong ultraviolet B emission due to the 6P7/2→8S7/2 transition of the Gd3+ ions was achieved. Under the excitation of a 450 nm blue laser, Pr3+ absorbed two blue photons to realize the upconversion process and then transferred the energy to Gd3+ to obtain the ultraviolet B emission.

Microstructure and photoluminescence properties of Er3+/LaBiO3 co-modified (K0.5Na0.5)NbO3 transparent textured ceramics via tape-casting method

A trade-off contradictory relationship between texturization and optical transparency exists in ferroelectric ceramics, so to achieve transparency in textured ferroelectrics is quite difficult. Here, Er3+ and LaBiO3 co-modified (K0.5Na0.5)NbO3 (1Er-KNN-yLB) transparent textured ceramics were successfully prepared by the tape-casting method. Doping of LaBiO3 enables the textured ceramics to exhibit excellent up-conversion photoluminescence properties, and the red emission is significantly improved. Meanwhile, with certain amount of LB content, the textured ceramics show nanoscale grains and approaching pseudo-cubic phase, resulting in high density and obvious relaxor-like behavior. This result indicates high local symmetry and less light scattering centers within the textured ceramics, finally bringing about enhanced optical transparency, with the highest transmittance of ∼ 39% in the visible region at y = 0.025. Additionally, the observable piezoelectric and ferroelectric performances were obtained. These multifunctional properties endow KNN-based textured ceramics with promising application prospects in optoelectronic devices.

Anomalous upconversion behavior and high-temperature spectral properties of Yb/Ho-SiAlON ceramics

Traditionally, NaYF4 and glass-based materials are considered the most efficient upconversion materials. However, those materials may show signs of thermal warping or risks of fracture during long-term service life in extreme environments. In contrast, SiAlON ceramics preserve their spectral and physical integrity during continuous use due to their ultra-low thermal expansion coefficient (∼3.0 × 10−6/K) even at extreme temperatures. Here, we investigate the upconversion photoluminescence properties of Ho and Yb co-doped SiAlON (Ho/Yb-SiAlON) ceramics, prepared by hot-press method, at room temperature and at high temperature (298–1023 K). At room temperature, Ho/Yb-SiAlON ceramics show intense red upconversion emission under 980 nm excitation. At the high-temperature range, the spectral shift is absent in Ho/Yb-SiAlON indicating that the SiAlON ceramics have high-temperature spectral stability, which may be attributed to the low thermal expansion coefficient of SiAlON ceramics. Ho and Yb concentration-dependent spectra show an anomalous upconversion emission behavior. It is found that a higher sensitizer and low activator concentration combination is not always an ideal choice for sensitized luminescence in SiAlON ceramics which is in stark contrast to the common understanding of sensitized luminescence. The mechanism involving the dominant cross-relaxation process has been proposed to explain the observed anomalous upconversion behavior.

Flexible piezoelectric nanogenerator based on the Er3 + doped lead-free (Na0.5Bi0.5)TiO3-BaTiO3 piezoelectric nanofibers with strong upconversion luminescence

Flexible piezoelectric nanogenerators (PENG) have attracted wide attention because of their great potential in solving the power supply problem of wearable electronic devices. In order to expand the applications of PENG, high quality (Na 0.5 Bi 0.5 )TiO 3 -0.06BaTiO 3 (NBT-0.06BT: x Er 3+ ) nanofibers doped with different Er 3+ concentrations were prepared by the gel-sol electrostatic spinning method. The morphology and phase structure of the prepared nanofibers were characterized. Dense nanofibers with good crystallization have been obtained. The local ferroelectric properties of the nanofibers were characterized by PFM. It is found the prepared nanofibers have a strong upconversion (UC) photoluminescence (PL) property. Utilizing the fluorescence intensity ratio (FIR ) technique, the temperature sensing properties of the nanofibers has been investigated, showing a maximum sensitivity of 0.0043 K −1 . Finally, the flexible PENG was prepared by encapsulating NBT-0.06BT:0.01Er 3+ nanofibers, interdigital electrode and PDMS. The maximum voltage output of PENG is 97 V. The present investigation integrates the luminescence characteristics and electrical properties of nanofibers into the flexible PENG, which may greatly expand its application field. • NBT-0.06BT: x Er 3+ nanofibers with high quality have been successfully prepared. • NBT-0.06BT: x Er 3+ nanofibers have excellent temperature sensing properties. • The present PENG has a potential application in optics. • The output voltage of the PENG reaches a high value of 97 V.

(INVITED)Judd-Ofelt analysis, visible to NIR photoluminescence emission under 450 nm and 976 nm excitations and energy transfer of barium fluorotellurite glasses doping with Ho3+, Yb3+, Ho3+:Yb3+

Barium fluorotellurite glasses doping with Ho3+, Yb3+, and Ho3+:Yb3 were fabricated using the conventional melt and quenching method, and their optical properties were studied using different optical spectroscopic techniques. The FITR absorption band at 3000 cm−1 was used to investigate OH- concentrations of the prepared glasses, which increased with Yb3+ content. However, it decreased by substituting a portion of BaF2 content with Ba2CO3 concentration. The electric dipole line strengths and Judd-Ofelt parameters were estimated using UV–visible near-infrared (NIR) optical absorption spectra to gain information on the rare earth ions doped glasses for laser applications. The various radiative parameters such as line strengths, optical intensity, and radiative rates from the higher energy levels, including 5F4+5S2, 5F5, 5I4,5I5,5I6 and 5I7, to the ground state, 5I8 have been reported and discussed. The influence of the Yb3+ and Ba2CO3 concentrations on the upconversion and downconversion photoluminescence emission intensities of the glasses prepared have been investigated by pumping with 450 nm and 976 nm excitation sources. Under 450 nm and 976 nm, the NIR photoluminescence emissions reveal a band ranging from 980 nm to 1220 nm attributing to an overlap between Yb3+ and Ho3+ transitions. The influence of Yb3+ concentration on photoluminescence lifetime at the 2F5/2→2F7/2, 5F4+5S2 →5I8 and 5I6 →5I8 transitions under 976 nm laser excitation has been studied and reported. The results indicate that lifetime decreases with increasing Yb3+ concentration attributing to an efficient energy transfer from Yb3+ to Ho3+ ions. The energy transfer efficiency from Yb3+ → Ho3+ has been examined, which rises from 30% to 47% upon increasing Yb3+ content. Nevertheless, it decreases with the mixing of BaF2 and Ba2CO3 lattice modifier contents. The results demonstrated that the 1200 nm (5I6 →5I8 transition) has remarkable potential for developing fiber lasers.

The downshifting and upconversion photoluminescence from NaBaSc2(PO4)3 for multicolor anti-counterfeiting

A novel langbeinite-type phosphate NaBaSc2(PO4)3 (NBSP) was synthesized by traditional solid-state reaction. The structure was refined on the basis of X-ray diffraction data. The Rietveld refinement result revealed that the structure of NBSP belongs to cubic system with space group P213 and cell parameters a = 10.0392 Å, b = 10.0392 Å, c = 10.0392 Å, α = β = γ = 90°, V = 1011.80 Å3, and Z = 4. The incorporations of Ce3+/Eu2+-Tb3+ into NBSP led to efficient downshifting emissions with adjustable color from blue to yellow. The luminescent properties, energy transfer and application in white light-emitting diode (WLED) were studied comprehensively. Moreover, blue, yellow and red upconversion emissions were also realized in NBSP by codoping Yb3+-Tm3+/Er3+/Ho3+, respectively. Finally, highly distinguishable luminescent images were obtained under the excitation of 254 nm, 365 nm or 980 nm, based on multiple NBSP phosphors with designed photoluminescence for the application in multicolor anti-counterfeiting. These results point out a practical approach for convenient and reliable anti-counterfeiting.

Higher-Order Multiphoton Absorption Upconversion Lasing Based on ZnO/ZnMgO Multiple Quantum Wells.

In the progress of nonlinear optics, multiphoton absorption (MPA) upconversion lasing enables many vital applications in bioimaging, three-dimensional optical data storage, and photodynamic therapy. Here, efficient four-photon absorption upconversion lasing from the ZnO/ZnMgO multiple quantum wells (MQWs) at room temperature is realized. Moreover, the MPA upconversion lasing and third-harmonic generation peak generated in the MQWs under the excitation of a femtosecond (fs) laser pulse were observed concurrently, and the essential differences between each other were studied comprehensively. Compared with the ZnO film, the upconversion lasing peak of the ZnO/ZnMgO MQWs exhibits a clear blue shift. In addition, the four-photon absorption upconversion photoluminescence (PL) intensity was enhanced in the MQWs/Au nanoparticles (NPs) by the metal-localized surface plasmons (LSPs). The work paves the way for short-wavelength lasers by taking advantage of the high stability and large exciton binding energy of the MQWs’ structures.

Highly efficient visible/near-infrared light photocatalytic degradation of antibiotic wastewater over 3D yolk-shell ZnFe2O4 supported 0D carbon dots with up-conversion property

The development of effective visible and near-infrared photocatalysts is highly promising in the current field of photocatalysis. Herein, carbon dots/ZnFe 2 O 4 (CDs/ZFO) with coating zero dimensional (0D) CDs on the surface of three dimensional (3D) yolk-shell ZFO spheres was designed and synthesized via a self-templated solvothermal method. The as-prepared CDs/ZFO composites displayed outstanding visible and near-infrared photocatalytic degradation activity of tetracycline (TC), and the optimal 3% CDs/ZFO sample with loading 3% (mass) CDs displayed the highest photocatalytic TC degradation ability under visible light (79.5% within 120 min) and near-infrared light (41% within 120 min). The enhancement of photocatalytic activity for CDs/ZFO composite is mainly ascribed to the fact that 0D/3D yolk-shell CDs/ZFO structure not only effectively reflect the incident light to increase the utilization efficiency of solar light, but also utilize the up-conversion photoluminescence and electronic conductivity properties of CDs to broaden sunlight absorption range and promote separation and transfer of electron-hole pairs.