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A visible light-activated photocathode fabricated with p-type semiconductor bismuth oxyiodide (BiOI) and graphene (G) was employed to investigate the photovoltammetric behavior of chloramphenicol (CAP). The result indicated that the voltammetric reduction peak of CAP increased to a limiting current platform under photoirradiation, owing to photoelectrocatalytic reduction of CAP on the BiOI-G photocathode. As a result, the cathodic photovoltammogram became sigmoidal in shape. Furthermore, the influences of graphene content in BiOI-G composites, scan rate and light intensity on the photovoltammetric behavior of CAP on the BiOI-G photocathode were systematically investigated. Based on such a BiOI-G electrode, a cathodic photovoltammetric sensor for CAP was proposed, which exhibited a current response linearly proportional to CAP concentration in the range of 0.5–50 μmol L−1, with a detection limit (3S/N) of 0.14 μmol L−1. Moreover, the photovoltammetric sensor displayed good reproducibility and high stability. The applicability of the proposed sensor was demonstrated by determining CAP in eye drop and environmental water samples.

A visible light-induced self-powered sensor for the detection of tyrosinase activity was proposed. A tyrosinase-responsive photoelectrochemical-chemical redox cycling strategy was integrated with a photofuel cell for signal amplification.

A series of novel Eu2+/3+, Ce3+ ion single- and co-doped BaZn2(PO4)2 samples were prepared via a high-temperature solid-state reaction. XRD powder diffraction results indicated that all of the products were pure phases. The photoluminescence properties of BaZn2(PO4)2:Eu showed that Eu2+ and Eu3+ coexist in the system and Eu3+ can be self-reduced to Eu2+ in an air atmosphere. In addition, the strongest emission peak of Eu3+ ions at 593 nm implied that Eu3+ ions occupy the inversion symmetry lattice and also the site of Zn in BaZn2(PO4). We used the theoretical method of bond energy to explain why the self-reduction of Eu3+ to Eu2+ can occur in the BaZn2(PO4)2 system. The calculation results indicated that the bond energy change value is smaller than , indicating that Eu2+ ions are more likely to occupy the Zn site and more stable than Eu3+ ions in BaZn2(PO4). Furthermore, the energy transfer process between Ce3+ and Eu2+ ions in the photoluminescence spectrum and the decay lifetime were observed, and the energy transfer mechanism was determined to be a dipole–dipole interaction. In this work, by adjusting the ratio of Ce and Eu ions, the emission color can be changed from blue to white, implying that the phosphor can be used as a promising candidate in the manufacture of white LEDs.

Early diagnosis is crucial to the treatment of cancer. Cathepsin B (CTB) plays an important role in numerous cancers, which is a promising biomarker for early diagnosis of cancer. It is necessary to exploit new probes for visualization of CTB in vivo. Fluorescent/photoacoustic (FL/PA) imaging is a powerful tool for in vivo study which possesses both excellent sensitivity and spatial resolution. To our knowledge, there has been no FL/PA probe to image CTB in vitro or in vivo. Therefore, we developed two CTB-activated FL/PA probes HCy-Cit-Val and HCy-Gly-Leu-Phe-Gly, which could successfully monitor CTB activity in vivo. Both two probes had excellent sensitivity and selectivity in vitro. Cell imaging showed that HCy-Cit-Val or HCy-Gly-Leu-Phe-Gly could image endogenous CTB in lysosome with 6.8-fold or 5.1-fold enhancement of the FL signal and 5.8-fold or 3.4-fold enhancement of the PA signal compared to their inhibitor contrast groups. Tumor imaging in vivo further confirmed the good applicability of these two probes to monitor CTB activity with high sensitivity and spatial resolution. Moreover, the property of HCy-Cit-Val is superior to HCy-Gly-Leu-Phe-Gly due to the higher catalytic efficiency of CTB toward HCy-Cit-Val than HCy-Gly-Leu-Phe-Gly. We envision that our FL/PA probe HCy-Cit-Val will be suitable for clinical early diagnosis of CTB-related cancer in the near future.

The existing valence state (Eu2+/Eu3+ and Tb3+/Tb4+) in Eu/Tb ions doped in SrAl2Si2O8 were investigated through experimental and theoretical method. Their photoluminescence properties indicated that parts of Eu3+ ions were reduced to Eu2+ in SrAl2Si2O8. Based on the bond energy method, the reduction process of the Eu3+→Eu2+ and the preferentially occupancy of Eu3+/Eu2+ in SrAl2Si2O8 samples have been discussed. The values of deviation of its bond energy were calculated when Eu ions located at different crystal sites. Theoretical results indicated that the Eu3+ and Eu2+ would preferentially occupy the Sr sites due to the smaller energy variation. In addition, the variation of bond energy of Eu3+( Δ E Eu 3 + - O 2 - Sr =11.367 kcal/mol) is close to Eu2+ ( Δ E Eu 2 + - O 2 - Sr = 15.112 kcal/mol), which indicated that the both of Eu2+ and Eu3+can stably exist in SrAl2Si2O8 host. When Eu, Tb ions are co-doped in SrAl2Si2O8, the photoluminescence shows that only the characteristic emission peaks of Eu2+ and Eu3+ can be found and the emission of Tb3+ disappeared. It is suggested that the Tb3+ is oxidized to Tb4+ and the Eu3+ is reduced to Eu2+. Compared with Eu ion, the variation of bond energy for Tb3+( Δ E Tb 3 + - O 2 - Sr =10.084 kcal/mol) is more closer to Tb4+ ( Δ E Tb 4 + - O 2 - Sr =9.628 kcal/mol), so in Tb3+, Eu3+ co-doped in SrAl2Si2O8, the Tb4+ ion has the highest priority to occupy the Sr sites, Tb3+ loses one electron to form the tetravalent Tb4+, and the excess electrons are transferred to the surrounding neighboring Eu3+ site, Eu3+ gets an electron and is reduced to Eu2+. The theoretical results are in accord with the experimental measurement.

Eu-doped MAlSi2O6 (M = Li, Na, K, Rb, Cs) phosphors were synthesized by solid-state reaction in air. The crystal structure and optical properties of the phosphors were investigated by X-ray powder diffraction and photoluminescence. Their emission spectra are composed of some broad bands coming from the 5d-4f transition of Eu2+ and some sharp emission peaks coming from the f-f transitions of Eu3+. The co-existence of Eu3+ and Eu2+ cations is detected in MAlSi2O6:2%Eu, which shows that the unusual Eu3+→Eu2+ reduction process occurs in MAlSi2O6. The preferential occupancy of Eu3+ or Eu2+ in MAlSi2O6 can be calculated to be M+ sites by the bond-energy method. The deviation of the Eu3+–O2- bond energy is closed to that of the Eu2+–O2- bond energy, which means that Eu3+ and Eu2+ can coexist in air. The abnormal reduction of Eu3+ to Eu2+ can be explained by charge compensation model. The doped Eu3+ was induced to M+ and the vacancy (VM) may be formed. The vacancy(VM) acted as a donor of electrons, and the Eu M ∙ ∙ defect acted as an acceptor of electrons. The theoretical result is consistent with the experimental phenomenon.

The vanadate-based phosphors Sr2V2O7:Eu3+ (SV:Eu3+), Sr9Gd(VO4)7:Eu3+ (SGV:Eu3+) and Sr9Gd(VO4)7/Sr2V2O7:Eu3+ (SGV/SV:Eu3+) were obtained by solid-state reaction. The bond-energy method was used to investigate the site occupancy preference of Eu3+ based on the bond valence model. By comparing the change of bond energy when the Eu3+ ions are incorporated into the different Sr, V or Gd sites, we observed that Eu3+ doped in SV, SGV or SV/SGV would preferentially occupy the smaller energy variation sites, i.e., Sr4, Gd and Gd sites, respectively. The crystal structures of SGV and SV, the photoluminescence properties of SGV:Eu3+, SV, SGV/SV and SGV/SV:Eu, as well as their possible energy transfer mechanisms are proposed. Interesting tunable colours (including warm-white emission) of SGV/SV:Eu3+ can be obtained through changing the concentration of Eu3+ or changing the relative quantities of SGV to SV by increasing the calcination temperature. Its excitation bands consist of two types of O2− → V5+ charge transfer (CT) bands with the peaks at about 325 and 350 nm respectively, as well as f–f transitions of Eu3+. The obtained warm-white emission consists of a broad photoluminescence band centred at about 530 nm, which originates from the O2− → V5+ CT of SV, and a sharp characteristic spectrum (5D0–7F2) at about 615 and 621 nm.

A bond-energy method is used to determine the site occupancy preference of Eu3+ or Eu2+ and further firstly extended to study the spontaneous reduction of Eu3+ doped CaAl2Si2O8 based on the bond valence model. The phosphor CaAl2Si2O8: Eu was synthesized under air condition. The co-existence of Eu3+ and Eu2+ cations was detected through photoluminescence measurement. The occupancy of Eu3+ or Eu2+ in CaAl2Si2O8 can be determined by comparing the deviation of its bond energy in different locations at Ca2+, Si4+ and Al3+ sites. Theoretical calculation result indicates that the Eu3+ and Eu2+ would preferentially occupy the smaller energy variation sites Ca4, which can be assigned to Eu4 site. The more important result is that the energy variation of Eu2+ at Eu4 sites is smaller than that of Eu3+ at the same sites, which indicates that Eu2+ is more stable than Eu3+ at Eu4 sites, so the spontaneous Eu3+→Eu2+ reduction can be found in the CaAl2Si2O8. The same bond energy method can be extended to explain the reason why the Sm3+ doped CaAl2Si2O8 can't be reduced into Sm2+ under reduction condition. The theoretical result is consistent with the experimental phenomenon. This should help us to have a further understanding of spontaneous Eu3+→Eu2+ reduction in the inorganic material.

Ca10M(PO4)7:Eu (M = Li, Na, K) phosphors have been synthesized via a solid-state reaction process, their phase purity was examined using XRD patterns, and Rietveld refinement confirmed that the Ca10Li(PO4)7, Ca10Na(PO4)7 and Ca10K(PO4)7 are pure phases. The photoluminescence properties of the Ca10M(PO4)7:Eu (M = Li, Na, K) phosphors showed that the self-reduction of Eu3+ to Eu2+ can occur in an air atmosphere. Eu3+ ions can be reduced to Eu2+ ions when doped in Ca10Li(PO4)7, Ca10Na(PO4)7 and Ca10K(PO4)7 crystals, which was detected using photoluminescence spectra. In this work, the bond energy method was used to determine and explain the mechanism of site occupation of Eu entering the host matrix. According to the calculated value of the deviation of bond energy for Eu3+-doped Ca10M(PO4)7 (M = Li, Na, K) crystals, the similar value between and , and , and and can provide the conditions for the self-reduction of Eu3+ in the Ca10M(PO4)7 (M = Li, Na, K) system. Meanwhile, the smaller deviation values of , , and in Ca10Li(PO4)7, Ca10Na(PO4)7, and Ca10K(PO4)7 crystals and in Ca10K(PO4)7 crystals indicated that the preferential sites of Eu ion occupancy in the Ca10M(PO4)7 (M = Li, Na, K) lattices are Li, Na, K and Ca sites. The conclusions obtained from the calculated results of the bond energy method are consistent with the Rietveld refinement and the photoluminescence spectra of Ca10M(PO4)7 (M = Li, Na, K).

The local crystal sites occupied by Eu3+ in Ca5(BO3)3F:1% Eu3+ phosphor were investigated experimentally and theoretically. Ca5(BO3)3F:1% Eu3+ was synthesized by high-temperature solid-state method in air. The crystal structure and optical properties of the phosphor were studied by X-ray powder diffraction and photoluminescence, respectively. Two different O2− → Eu3+ CT broad bands with the peaks at 266 and 283 nm in Ca5(BO3)3F:1% Eu3+ were detected, indicating the Eu3+ sites occupied Ca2 and Ca1, respectively. The different sharp f–f emission spectra under the excitation of 283 and 266 nm proved that there are two different local lattice environments around Eu3+ existing in Ca5(BO3)3F:1% Eu3+. Environmental factor he, the standard deviation of environmental factor (EFSD) and the bond energy were used to illustrate and explain the site occupancy mechanism of Eu3+ into the host lattice. By comparing the intensity ratios of 5D0 → 7F2 transition to the 5D0 → 7F1 transition, I(5D0/7F2)/I(5D0/7F1) of Eu3+ at Ca2 (7.381) was found to be 2.5 times stronger than that of Eu3+ at Ca1 site (2.933). was calculated to analyze the I(5D0/7F2)/I(5D0/7F1) value. On the basis of the bond valence model, a bond-energy method was used to study the occupancy of the Eu ion, which indicated that the preferential sites of Eu ion occupancy in the Ca5(BO3)3F are the Ca2 and Ca1 sites. All three theoretical calculation results are consistent with each other.

CaY1−xAl1+xO4:2%Eu (x = 0, 0.1, 0.2) phosphors have been synthesized via a solid-state reaction process. XRD patterns indicate that they are pure phase. The photoluminescence properties of the CaY1−xAl1+xO4:2%Eu phosphors exhibit both the blue emission of Eu2+ (4f65d1–4f7) and red-orange emission of Eu3+ (5D0–7F1,2,3,4) under UV light excitation, which showed that the Eu3+/2+ co-doping system was obtained by adjusting the Al/Y ratio. Eu3+ ions can be reduced to Eu2+ ions when the Al/Y ratio was changed. In this work, the bond energy method was used to determine and explain the mechanism of the site occupation of Eu ions entering the host matrix. Also, the emission spectrum showed an unusual comparable intensity 5D0–7F4 transition peak. The relative intensity of 5D0–7F2 and 5D0–7F4 can be stabilized by changing the relative proportions of Al3+ and Y3+. Furthermore, this was explained by the J–O theory.

It is considerably meaningful to fabricate a second near-infrared spectral region (NIR-II, 1000–1700 nm) responsive theranostic nanoplatform simultaneously possessing good stability and biocompatibility for efficient and safe cancer treatment. In this work, as a flexible strategy, an intelligent nanoplatform was prepared by using water-soluble cyclic oligosaccharides α-cyclodextrin (α-CD) to load photosensitizer Chlorin e6 (Ce6) onto Fe3O4@Cu2−xS core−shell nanoparticles (NPs). The as-synthesized Fe3O4@Cu2−xS-Ce6/α-CD NPs are ultrasmall (≈5 nm) and aqueously dispersible, which offer both biocompatibility and renal clearance. Resultly, the obtained Fe3O4@Cu2−xS-Ce6/α-CD NPs feature remarkable absorption in the second near-infrared region (NIR-II), which can provide advantages of large penetration depth and high photothermal conversion efficiency (η = 67.88%). Additionally, the introduction of Ce6 can trigger the generation of 1O2 under visible light irradiation. Therefore, it provides the proof-of-concept application of functional materials in photodynamic and photothermal combination cancer therapy.

CuO-Cu2O heterojunction was synthesized via a one-step flame spray pyrolysis (FSP) process and employed as photoactive material in construction of a photoelectrochemical (PEC) sensing device. The surface analysis showed that CuO-Cu2O nanocomposites in the size less than 10 nm were formed and uniformly distributed on the electrode surface. Under visible light irradiation, the CuO-Cu2O-coated electrode exhibited admirable cathodic photocurrent response, owing to the favorable property of the CuO-Cu2O heterojunction such as strong absorption in the visible region and effective separation of photogenerated electron-hole pairs. On the basis of the interaction of l-cysteine (l-Cys) with Cu-containing compounds via the formation of Cu-S bond, the CuO-Cu2O was proposed as a PEC sensor for l-Cys detection. A declined photocurrent response of CuO-Cu2O to addition of l-Cys was observed. Influence factors including CuO-Cu2O concentration, coating amount of CuO-Cu2O, and applied bias potential on the PEC response toward l-Cys were optimized. Under optimum conditions, the photocurrent of the proposed sensor was linearly declined with increasing the concentration of l-Cys from 0.2 to 10 μM, with a detection limit (3S/N) of 0.05 μM. Moreover, this PEC sensor displayed high selectivity, reproducibility, and stability. The potential applicability of the proposed PEC sensor was assessed in human urine samples.

A novel adjustable dual excited emission Eu2+/Eu3+ co-doped Ca4Si2O7F2 phosphor are reported. Unlike most of Eu2+ doped inorganic compounds, in the host lattice Ca4Si2O7F2, partial Eu3+ can still exist stably even in reducing atmosphere. The adjustable dual excited emission from blue light to red light can be found by changing the wavelength of excitation emission or the concentration of europium doped ion. The mechanism by which the two ions Eu2+ and Eu3+ can coexist in Ca4Si2O7F2 is revealed through the bond energy theory. Eu2+ and Eu3+ in Ca4Si2O7F2 system can be demonstrated to occupy the Ca1 lattice of Ca4Si2O7F2.

A photocathode-based photocatalytic fuel cell (PFC) was fabricated and proposed as a self-powered sensor for p-nitrophenol (p-NP) detection. The PFC was comprised of a photocathode and an anode in separated chambers, which could generate suitable power output under photoirradiation to drive the sensing process. In this device, p-type PbS quantum dots-modified glass carbon electrode (GCE) served as the photocathode for the reduction of p-NP under photoirradiation while graphene-modified GCE was employed as the anode for the oxidation of ascorbic acid. In order to improve the selectivity of the PFC sensor, p-NP binding molecularly imprinted polymer (MIP) was introduced on the photocathode. Under optimal conditions, the open circuit voltage of the constructed PFC sensor was found to sensitively respond to p-NP in a wide concentration range from 0.05 μM to 20 μM. The proposed sensor exhibited high selectivity, good reproducibility, and stability, demonstrating the successful combination of MIP with photocathode in construction of high-performance PFC self-powered sensors for pollutant monitoring.

Photovoltammetric behaviors of irreversible, quasi-reversible and reversible electrochemical systems represented by 2,4-dichlorophenol (DCP), hydroquinone (HQ) and K3 [Fe(CN)6 ], respectively, were investigated on a CdS-graphene hybrid film electrode. The cyclic voltammetric (CV) curves of HQ and K3 [Fe(CN)6 ] showing a pair of redox peaks became sigmoidal in shape under visible light irradiation. In contrast, the CV curve shape of DCP showing an oxidation peak was not changed under photoirradiation, although the oxidation peak current was enhanced by the photoelectrocatalysis. Thus, the reversibility-dependent photovoltammetric behaviors were observed. Furthermore, it was demonstrated that the photovoltammetric curve shapes were not changed by pH and intensity of light source, but were tunable with scan rate and concentration of reactants depending on the reversibility of the electrochemical reactions.

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Encapsulated beta cell transplantation offers a potential cure for a subset of diabetic patients. Once transplanted, beta cell grafts can help to restore glycemic control; however, locating and retrieving cells in the event of graft failure may pose a surgical challenge. Here, a dual-function nanoparticle-loaded hydrogel microcapsule is developed that enables graft retrieval under an applied magnetic field. Additionally, this system facilitates graft localization via magnetic resonance imaging (MRI), and graft isolation from the immune system. Iron oxide nanoparticles encapsulated within alginate hydrogel capsules containing viable islets are transplanted and the in vitro and in vivo retrieval of capsules containing nanoparticles functionalized with various ligands are compared. Capsules containing islets co-encapsulated with COOH-coated nanoparticles restore normal glycemia in immunocompetent diabetic mice for at least 6 weeks, can be visualized using MRI, and are retrievable in a magnetic field. Application of a magnetic field for 90 s via a magnetically assisted retrieval device facilitates rapid retrieval of up to 94% (±3.1%) of the transplant volume 24 h after surgical implantation. This strategy aids monitoring of cell-capsule locations in vivo, facilitates graft removal at the end of the transplant lifetime, and may be applicable to many encapsulated cell transplant systems.