Au/NaYF4 : Yb,Er Binary Superparticles: Synthesis and Optical Properties

Colloidal superparticles (SPs) are nanoparticle (NP) assemblies in the form of colloidal particles. Assembling nanoscopic objects into mesoscopic or macroscopic composite architectures allows for the bottom-up fabrication of functional nanomaterials. In this study, a method for single-step self-assembly synthesis of Au/NaYF₄ : Yb,Er SPs was developed using oil-in-water (O/W) microemulsions to simultaneously encapsulate gold nanoparticles (AuNPs) and NaYF₄ : Yb,Er upconversion nanoparticles (UCNPs) via evaporation at room temperature. The synthesized Au/NaYF₄ : Yb,Er SPs possess good dispersibility and stability. When the number of AuNPs added is increased, the SPs exhibit decreased upconversion luminescence, which can be ascribed to the Förster resonance energy transfer (FRET) from the NaYF₄ : Yb,Er UCNPs to the AuNPs. Time-resolved measurements of the green emission further confirm the existence of a new decay route corresponding to the FRET process. Our research provides a facile and versatile strategy for the synthesis of novel multifunctional nanocomposites with tunable upconversion luminescence properties, which can be of great significance in biological applications.     

BaCl2:Er3+—A High Efficient Upconversion Phosphor for Broadband Near‐Infrared Photoresponsive Devices

Utilization of photons with subband‐gap energy, mostly near‐infrared (NIR) photons, is highly desirable for photovoltaic cells; which can be achieved by adding an upconversion layer at the rear face of photovoltaic cells. Here, we study the upconversion luminescence properties of BaCl₂:Er³⁺ phosphors and hexagonal NaYF₄:Er³⁺ phosphors upon excitation of incoherent NIR sunlight with wavelength λ > 800 nm. Higher efficacious upconversion emissions of BaCl₂:Er³⁺ phosphors have been observed in comparison with the well‐known hexagonal NaYF₄:Er³⁺ phosphors. We demonstrate that the photocurrent response from the thin‐film‐hydrogenated amorphous silicon solar cell attached with the BaCl₂:Er³⁺ phosphor is notably enhanced under irradiation of incoherent NIR sunlight with wavelength λ > 800 nm. This judicious design may be envisioned to shorten the distance for the remarkable improvement of the power conversion efficiency of the next‐generation photovoltaic cells and suggests a promising application for other NIR photoresponsive devices.     

Plasmon-enhanced upconversion luminescence with the hybrid structure of semiconductor-insulator-semiconductor

High-quality hexagonal NaYF₄:Er/Yb particles and monodisperse copper(I) sulfide nanoparticles (NPs) were obtained with the solvothermal method and the hot-injection method, respectively. The hybrid structure of semiconductor-insulator-semiconductor (SIS) was constructed for upconversion luminescence (UCL). The results showed that compared with that of NaYF₄:Er/Yb-SiO₂ particles, the luminous intensity of SIS was promoted by 12.5 folds, and the quantum yield of SIS can reach to 0.89%. Furthermore, the optical field distribution in the vicinity of hybrid structure of SIS was numerically simulated based on the finite-time domain-difference method (FDTD). The UCL enhancement of the SIS originates from the amplified optical field, which was attributed to the localized surface plasmon resonance (LSPR) effect of copper(I) sulfide NPs and the local effect of the copper(I) sulfide film on the excited light.     

Upconversion of NaYF4: Yb,Er Nanoparticles Co-doped with Zr 4+ for Magnetic Phase Transition and Biomedical Imaging Applications

Tracking of cancer cells and cytotoxicity of normal tissue are the leading problem in cancer treatment. The magnetic and fluorescent multifunctional particles evolve as an emerging alternative for future target recognition. The ferromagnetic materials potentially treat the defects in the gene. Hence, ferromagnetic materials are the best for the treatment of cancer using gene therapy. Here, β-NaYF₄: Yb, Er compounds doped with 10%, 20% and 30% Zirconium (Zr) are prepared through hydrothermal technique. Citrate itself is a highly biocompatible surface ligand that labels the imaging probe. The X-ray diffraction analysis is evident for transforming hexagonal to cubic phase via Zr doping in NaYF₄: Yb, Er compounds. The electron microscopic images identify the hexagonal plates. This compound can emit visible light in response to infrared (IR) light irradiation. Especially β-NaYF₄: Yb, Er, and 10% of Zr, Yb, Er tridoped NaYF₄ compounds show enhanced red emission exploited in bioimaging applications. Insignificantly, 30% of Zr, Yb, Er tridoped NaYF₄ concentration exhibit hexagonal and dominating cubic (α) phase, could decrease red emissions intensity and magnetisation value. This Zr material reveals peculiar magnetic properties, especially ferromagnetism at a lower magnetic field and produces paramagnetism at a higher magnetic field. Here, 10–20% Zr, Yb, Er tridoped NaYF₄ concentrations exhibit better magnetic properties. The resultant compound is viable for the VERO cells.

     

Upconversion luminescence enhancement of NaYF4:Yb3+,Er3+ nanocrystals induced by the surface plasmon resonance of nonstoichiometric WO2.72 semiconductor

Upconversion luminescence of rare‐earth ions doped nanoparticles can be enhanced by the localized surface plasmon resonance (LSPR) of noble metals nanoparticles, which was extensively investigated. The semiconductor nanomaterials such as the WO_2.72 exhibited the tunable LSPR, which provide the possibility for the luminescence enhancement of upconversion nanoparticles. In this work, the urchin‐like WO_2.72 was successfully prepared by solvothermal method, exhibiting the LSPR in the near infrared region. The influence of LSPR of WO_2.72 on the upconversion luminescence of NaYF₄:Yb³⁺,Er³⁺ nanoparticles was investigated firstly. The 525, 542, and 660 nm upconversion luminescence of NaYF₄: Yb³⁺,Er³⁺ nanoparticles was increased by the 10, 8, and 12 factors, respectively, which was from the enhanced excitation field induced by the WO_2.72 film.     

The Effect of Coatings on the Affinity of Lanthanide Nanoparticles to MKN45 and HeLa Cancer Cells and Improvement in Photodynamic Therapy Efficiency

An improvement in photodynamic therapy (PDT) efficiency against a human gastric cancer cell line (MKN45) with 5-aminolevulinic acid (ALA) and lanthanide nanoparticles (LNPs) is described. An endogenous photosensitizer, protoporphyrin IX, biosynthesized from ALA and selectively accumulated in cancer cells, is sensitizable by the visible lights emitted from up-conversion LNPs, which can be excited by a near-infrared light. Ten kinds of surface modifications were performed on LNPs, NaYF₄(Sc/Yb/Er) and NaYF₄(Yb/Tm), in an aim to distribute these irradiation light sources near cancer cells. Among these LNPs, only the amino-functionalized LNPs showed affinity to MKN45 and HeLa cancer cells. A PDT assay with MKN45 demonstrated that amino-modified NaYF₄(Sc/Yb/Er) gave rise to a dramatically enhanced PDT effect, reaching almost perfect lethality, whereas NaYF₄(Yb/Tm)-based systems caused little improvement in PDT efficiency. The improvement of PDT effect with the amino-modified NaYF₄(Sc/Yb/Er) is promising for a practical PDT against deep cancer cells that are reachable only by near-infrared lights.     

Near/mid‐infrared emission and energy transfer of Er/Tm‐Yb co‐doped β‐NaYF4 microcrystals

The well‐formed high quality β‐NaYF₄:Er³⁺/Tm³⁺, Yb³⁺ microcrystals with near/mid‐infrared (NIR/MIR) emission are synthesized by the solvothermal method. Obvious 1.4 μm, 1.8 μm emissions, and 1.5 μm emission are observed in as‐prepared β‐NaYF₄:Tm³⁺, Yb³⁺ and β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals, respectively. To obtain MIR emission, the as‐prepared β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals are heat‐treated at different temperature schedule and atmosphere, it demonstrates there is great effect on the morphology and crystal structure when heat‐treated at different temperature, while little effect under different heat‐treated atmosphere. Subsequently, after heat‐treatment at 575°C in air, owing to the efficient elimination of internal defects and partly surface hydroxyl/citrate groups, an obvious 2.7 μm MIR emission is successfully detected in heat‐treated β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals for the first time.     

Influence of Yb Concentration on the Optical Properties of CaF2 Transparent Ceramics Codoped with Er and Yb

Er, Yb:CaF₂ nanoparticles with different Yb concentrations were synthesized by a coprecipitation method using nitrates as raw materials. X‐ray powder diffraction and transmission electron microscopy analysis showed that the nanoparticles were single fluorite phase and the nanoparticle size was found to decrease with increasing Yb concentrations. The obtained nanoparticles were hot‐pressed at 800°C under 30 MPa under vacuum environment to fabricate Er, Yb:CaF₂ transparent ceramics. The influence of Yb ion concentrations on the optical transmission, microstructure, and luminescence properties of Er, Yb:CaF₂ transparent ceramics were investigated. The addition of Yb ions was found effectively to reduce grain size and has a positive effect on improving the optical transmission of Er, Yb:CaF₂ transparent ceramics. The highest transmittance in the near‐infrared spectral region of the Er, Yb:CaF₂ transparent ceramic reached about 90%. The green, red, and near‐infrared emission intensities were found to increase with increasing Yb concentration.     

Enhanced Solid‐Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)‐TiO2 Nanocomposite Film with Bismuth Oxyiodide

A new type of photodegradable poly(vinyl chloride)‐bismuth oxyiodide/TiO₂ (PVC‐BiOI/TiO₂) nanocomposite film was prepared by embedding a nano‐TiO₂ photocatalyst modified by BiOI into the commercial PVC plastic. The solid‐phase photocatalytic degradation behavior of the as‐prepared film was investigated in ambient air at room temperature under UV light irradiation, with the aid of UV‐Vis spectroscopy, weight loss monitoring, scanning electron microscopy, and FT‐IR spectroscopy. Compared to the PVC‐TiO₂ nanocomposite film, the PVC‐BiOI nanocomposite film and the pure PVC film, the PVC‐BiOI/TiO₂ nanocomposite film exhibited a higher photocatalytic degradation activity. The optimal mass ratio of BiOI to TiO₂ was found to be 0.75 %. The weight loss rate of the PVC‐BiOI/TiO₂ nanocomposite film reached 30.8 % after 336 h of irradiation, which is 1.5 times higher than that of the PVC‐TiO₂ nanocomposite film under identical conditions. The solid‐phase photocatalytic degradation mechanism of the nanocomposite films was briefly discussed.     

Efficient dual‐mode up‐conversion and down‐shifting emission in β‐NaYF4:Yb3+,Er3+ microcrystals via ion exchange

We report efficient dual‐mode up‐conversion (UC) and down‐shifting (DS) emission in a single Yb³⁺/Er³⁺‐co‐doped β‐NaYF₄ microcrystals with controlled morphology and size via a simple Na⁺ ion‐exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal‐synthesized β‐NaYF₄. Meanwhile, IEM gives rise to the significant enhancement of UC emission intensity up to 3800 times and strongly enhanced DS emission intensity of Er³⁺ and Yb³⁺ by several times in β‐NaYF₄:Yb³⁺,Er³⁺ microcrystals. IEM also strongly prolongs the DS emission lifetimes of Er³⁺ and Yb³⁺ in visible and near‐infrared region. The enhanced UC and DS emission intensities and prolonged lifetimes in β‐NaYF₄:Yb³⁺,Er³⁺ are mainly ascribed to the dispersing of localized Yb³⁺ and Er³⁺ clusters during IEM.     

Near infrared light-induced photocurrent in NaYF4:Yb3+, Er3+/WO2.72 composite film

Spectral conversion technology based on NaYF₄:Yb³⁺, Er³⁺ upconversion nanoparticles was extensively used to improve photovoltaic conversion efficiency of solar cells. However, the response mismatch between absorption of semiconductors and upconversion luminescence (UCL) limits the application of spectral conversion technology. Nonstoichiometric WO_2.72 nanoparticles display the broad absorption from visible to near-infrared region due to the presence of oxygen vacancy, which is overlapped with the UCL of NaYF₄:Yb³⁺, Er³⁺ nanoparticles. Thus, the combination between NaYF₄:Yb³⁺, Er³⁺ nanoparticles, and nonstoichiometric WO_2.72 provides a possibility for designing a novel UCL spectral converted solar cells. In this work, composite film consisted of NaYF₄:Yb³⁺, Er³⁺ nanoparticles, and WO_2.72 nanofibers was prepared. The UCL of NaYF₄:Yb³⁺, Er³⁺/WO_2.72 film was decreased in contrast to pure NaYF₄:Yb³⁺, Er³⁺ nanoparticles due to energy transfer from NaYF₄:Yb³⁺, Er³⁺ nanoparticles to WO_2.72 nanofibers. The NaYF₄:Yb³⁺, E³⁺/WO_2.72film exhibits the photocurrent generation upon the 980 nm excitation. This novel UCL spectral converted solar cells based on the broad absorption of defects in the WO_2.72 host will provide a novel view for photovoltaic devices.     

Barrier,Biodegradation, and mechanical properties of (Rice husk)/(Montmorillonite) hybrid filler‐filled low‐density polyethylene nanocomposite films

Rice husk (RH)/montmorillonite (MMT) hybrid filler‐filled low‐density polyethylene nanocomposite films were prepared by extrusion blown film. RH was used as a biodegradable filler in various concentrations (2, 5, and 7 parts per hundred composite), while the amount of MMT was held constant at 2 wt%. Delamination of MMT platelets and distribution of RH were investigated by X‐ray diffraction and scanning electron microscopy. Diffractograms revealed the formation of intercalated structures, regardless of the RH content. Barrier properties revealed that MMT platelets have the potential to retard the diffusion of permeating molecules while, on the other hand, barrier efficiency of MMT is balanced by the subsequent incorporation of RH in RH/MMT hybrid filler‐filled composite films. Despite an increase in permeability, the selectivity ratio (CO₂/O₂ permeability) increased with increasing RH contents in the hybrid filler‐filled composite films showing the potential of these films in the development of modified atmosphere for fresh fruits and vegetables. The colonization of fungus and formation of holes as observed in micrographs of the test samples subjected to soil burial revealed that the biodegradation rate increased with the incorporation of RH in the hybrid composites. The composite films with higher contents of RH in hybrid filler are also more biodegradable than those having lower contents. Addition of RH contents in the hybrid filler increased the tensile modulus, while decreasing the tensile and tear strength. Addition of RH in the hybrid filler increased the melting and crystallization temperatures of the resulting nanocomposite films as well. J. VINYL ADDIT. TECHNOL., 23:162–171, 2017. © 2015 Society of Plastics Engineers     

Enhanced ultraviolet–visible–near infrared driven photocatalytic activity of 1D/0D BiVO4:Er/Yb@Ag/Ag3PO4 Z-scheme heterostructure via a synergetic strategy of plasmonic effect and upconversion luminescence

Expanding the spectral response range to near-infrared (NIR) region and improving carrier separation are the two critical strategies to obtain highly efficient photocatalysts for water pollution control. Herein, a new type of photocatalyst one-dimensional/zero-dimensional (1D/0D) BiVO₄:Er/Yb@Ag/Ag₃PO₄ Z-scheme heterostructure with full spectral response is constructed by an electrospinning coupled with an ethylene glycol assisted hydrothermal method. The optimized BiVO₄:Er/Yb@Ag/Ag₃PO₄ heterostructured nanofibers degrade 69.5% (9 h) and 91.3% (30 min) of tetracycline hydrochloride (TC), 76.7% (9 h) and 99.4% (24 min) of methylene blue (MB) and 38.2% (9 h) and 94.5% (60 min) of bisphenol A (BPA) under NIR light and simulated sunlight excitation, respectively. Under NIR light and simulated sunlight excitation, the MB removal efficiencies of the optimal composite are 9.833 and 1.094 times of Ag₃PO₄ and 20.184 and 11.558 times of BiVO₄, respectively. The superior photocatalytic activity can be attributed to the synergistic effects of the unique 1D/0D contact interface, the porous outer wall of BiVO₄:Er/Yb nanofibers, Ag bridged Z-scheme heterostructure, upconversion (UC) luminescence and the surface plasmon resonance (SPR) effect. This makes BiVO₄:Er/Yb@Ag/Ag₃PO₄ heterostructured nanofibers have the advantages of broadened absorption spectrum, abundant active sites, increased specific surface area, fast electron transfer channels, improved carrier separation efficiency, enhanced photocorrosion resistance and stability. This work provides a new insight in designing and constructing high-performance Ag bridged Z-scheme heterostructure photocatalysts with full spectral response for water pollution control.     

One‐pot combustion synthesis and efficient broad spectrum photoactivity of Bi/BiOBr:Yb,Er/C photocatalyst

A highly efficient broad spectrum responsive Bi/BiOBr:Yb,Er/C ternary composite was synthesized by a simple one‐pot combustion method using nitrates and citric acid as raw materials. Experimental results show that Er³⁺/Yb³⁺ were successfully doped into BiOBr lattice, and metallic Bi nanoparticles and carbon species were formed simultaneously. Compared with pure BiOBr and Bi/BiOBr/C, as‐synthesized Bi/BiOBr:Yb,Er/C ternary photocatalyst is highly responsive in the UV‐visible‐NIR range, and possesses the best photodegradation performance for Rhodamine B, phenol, and imidacloprid under visible, NIR, or solar light irradiation, which can be attributed to the synergetic effects of surface plasma resonance of metallic Bi, up‐conversion transition of Er³⁺ and heterojunctions (Bi/BiOBr, Bi/C, and BiOBr/C). Moreover, a plausible mechanism was given, the main active species, and photostability of samples were studied. The solar light photoactivity and influences of pH value and anions (Cl^?, SO₄^2?, CO₃^2?, HCO₃^?, and NO₃^?) were also investigated. This study highlights the advantages of synergetic effects of SPR, up‐conversion and heterojunctions, which provides a useful guide toward the rational design of broad spectrum (UV‐visible‐near infrared) photocatalysts.     

Morphology and properties of poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene]/silica nanoparticle hybrid films

Poly[2‐methoxy‐5‐(2′‐ethyl‐hexyloxy)‐para‐phenylene vinylene] (MEH‐PPV)/silica nanoparticle hybrid films were prepared and characterised. Three kinds of materials were compared: parent MEH‐PPV, MEH‐PPV/silica (hybrid A films), and MEH‐PPV/coupling agent MSMA/silica (hybrid B films), in which MSMA is 3‐(trimethoxysilyl) propyl methacrylate. It was found that the hybrid B films could significantly prevent macrophase separation, as evidenced by scanning electron and fluorescence microscopy. Furthermore, the thermal characteristics of the hybrid films were largely improved in comparison with the parent MEH‐PPV. The UV‐visible absorption spectra suggested that the incorporation of MSMA‐modified silica into MEH‐PPV could confine the polymer chain between nanoparticles and thus increase the conjugation length. The photoluminescence (PL) studies also indicated enhancement of the PL intensity and quantum efficiency by incorporating just 2 wt% of MSMA‐modified silica into MEH‐PPV. However, hybrid A films did not show such enhancement of optoelectronic properties as the hybrid B films. The present study suggests the importance of the interface between the luminescent organic polymers and the inorganic silica on morphology and optoelectronic properties. Copyright © 2004 Society of Chemical Industry     

The LSPR regulation of TiO2: W nanocrystals and its application in enhanced upconversion luminescence

The localized surface plasmon resonance (LSPR) absorption peaks of semiconductor nanocrystals are mainly concentrated in the infrared band, and the absorption characteristics can be controlled by the amount of element doping. The coupling of upconversion nanocrystals (UCNPs) and semiconductor nanocrystals can improve the upconversion luminescence (UCL) of rare-earth ions. Here, the LSPR absorption and morphology of the semiconductor nanocrystalline TiO₂: W were adjusted by using ammonium fluoride during synthesis. Significant absorption enhancement of TiO₂: W in the near-infrared region was obtained to enhance the UCL of NaYF₄: Yb³⁺, Er³⁺. The Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ layered structure films were fabricated through spin coating. Compared with Glass/NaYF₄: Yb³⁺, Er³⁺, the green and red lights of the Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ films were enhanced by 15.9 and 17.8 times, respectively. The UCL enhancement of Glass/NaYF₄: Yb³⁺, Er³⁺/TiO₂: W@SiO₂ was derived from the LSPR property of TiO₂: W through the enhancement of the excitation. The present work is important for possible applications of these layered structures as biomarkers, photocatalysts, flexible materials, and photoluminescence display panels.     

Effect of Yb Codoping on the Phase Transition,and Electrical and Photoluminescence Properties in KNLN:Er/xYb Ceramics

Ceramics 0.94(K_0.5Na_0.5)NbO₃?0.06LiNbO₃:Er/xYb with x = 0, 0.002, 0.004, 0.006, 0.008 were fabricated in this study, and phase structure, dielectric, piezoelectric, ferroelectric, and upconversion photoluminescence properties of the ceramics were systematically studied. Results show that all ceramics are in the polymorphic phase transition region near room temperature. However, a relaxor‐like phase transition was observed as Yb increasing to over x = 0.004. The optimized dielectric, piezoelectric, and ferroelectric properties, and maximized photoluminescence intensity ratio are obtained at x = 0.004. And the electrical and photoluminescence properties of the ceramics were discussed from the point view of the normal to relaxor‐like ferroelectric phase transition. The present study demonstrates that both the electrical and upconversion photoluminescence properties of the ceramics have an intimate correlation with the normal to relaxor‐like ferroelectric transition induced by Yb doping.     

Poly(glycidyl methacrylate‐co‐3‐thienyl‐methylmethacrylate) based working electrodes for hydrogen peroxide biosensing

BACKGROUND: Hydrogen peroxide biosensors based on Poly(glycidyl methacrylate‐co‐3‐thienylmethylmethacrylate)/ Polypyrrole [Poly(GMA‐co‐MTM)/PPy] composite film were reported. Poly(GMA‐co‐MTM) including various amounts of GMA and MTM monomers was synthesized via the radical polymerization. Enzyme horseradish peroxidase (HRP) was trapped in Poly(GMA‐co‐MTM)/PPy composites during the electropolymerization reaction between pyrrole and thiophene groups of MTM monomer, and chemically bonded via the epoxy groups of GMA. Analytical parameters of the fabricated electrodes were calculated and are discussed in terms of film electroactivity and mass transfer conditions of the composite films. RESULTS: The amount of electroactive HRP was found to be 1.25, 0.34 and 0.213 µg for the working electrodes of Poly(GMA_30%‐ co‐MTM_70%)/PPy/HRP, Poly(GMA_85%‐co‐MTM_15%)/PPy/HRP and Poly(GMA_90%‐co‐MTM_10%)/PPy/HRP, respectively. Optimal response of the fabricated electrodes was obtained at pH 7 and an operational potential of ? 0.35 V. It was observed that effective enzyme immobilization and electroactivity of the composite films could be changed by changing the ratios of GMA and MTM fractions of Poly(GMA‐co‐MTM) based working electrodes. CONCLUSION: The amount of electroactive enzyme increases with increasing MTM content of the final copolymer. High operational stabilities of the biosensors can be attributed to the strong covalent enzyme linkage via the epoxy groups of GMA due to preventing enzyme deterioration and loss. A more convenient microenvironment for mass transfer was provided for the electrodes by higher GMA ratios. It is observed that mass transfer is dominated by the mechanism of electron transfer to obtain effective sensitivity values. This work contributes to discussions clarifying the problems regarding the design parameters of biosensors. Copyright © 2011 Society of Chemical Industry     

TiO2‐kaolin‐PE composite film: A study based on photocatalytic degradation and biodegradation

A novel photodegradable and biodegradable polyethylene (PE) film was prepared through a melt blending technique, where nano‐TiO₂ and common kaolin were used as the photocatalyst and biodegradable promoter showing improved degradable efficiency of the waste PE. The photo‐degradation of the composite film was investigated by weight loss monitoring, attenuated total reflection–fourier transformed infrared spectroscopy (ATR–FTIR), and scanning electron microscopy. The aerobic biodegradation of the residue films after photodegradation was investigated by analysis of evolved carbon dioxide of films in aquatic test systems according to the international standards (ISO 14852, 1999). The results showed that the weight loss of as‐prepared photo‐ and biodegradable composite film reached 26.8% after 240 h of UV light irradiation. The big cavities formed not only on the film surface but also inside the bulk film, together with the chalking phenomenon taking place. The biodegradation results revealed that the addition of kaolin enhanced the degradation of UV‐light treated TiO₂‐PE films. The prepared PE based composite films showed promising application as novel photo‐biodegradable environment‐harmless materials. In addition, a degradation mechanism for this composite film was also discussed. POLYM. COMPOS., 37:2353–2359, 2016. © 2015 Society of Plastics Engineers     

Green Up‐Conversion Photoluminescence and Dielectric Relaxation of Ho3+/Yb3+‐Codoped Bi2Ti2O7 Pyrochlore Thin Films

Ho³⁺/Yb³⁺‐codoped Bi₂Ti₂O₇ pyrochlore thin films were prepared by a chemical solution deposition method, and their visible up‐conversion (UC) photoluminescence and dielectric relaxation were studied. Ho and Yb can be doped into Bi₂Ti₂O₇ lattice and single pyrochlore phase is maintained. Intense visible UC photoluminescence can be observed under the excitation of a 980‐nm diode laser. Two UC emission bands centered at 551 nm and 665 nm in the spectra can be assigned to ⁵F₄, ⁵S₂→⁵I₈ and ⁵F₅→⁵I₈ transitions of Ho³⁺ ions, respectively. The dependence of their UC emission intensity on pumping power indicates that both the green and red emissions of the thin films are two‐photon process. In addition, a Stokes near‐infrared emission centered at 1200 nm can be detected, which is due to ⁵I₆→⁵I₈ transition of Ho³⁺ ions. The thin films prepared on indium tin oxide–coated glass substrates exhibit a relatively high dielectric constant and a low dielectric loss as well as a good bias voltage stability. The dielectric relaxation of the thin films was also analyzed based on the temperature‐ and frequency‐dependent dielectric properties. This study suggests that Ho³⁺/Yb³⁺‐codoped Bi₂Ti₂O₇ thin films are promising materials for developing multifunctional optoelectronic thin film devices.