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Achieving bright photon upconversion under low irradiance is of great significance and finds many stimulating applications from photovoltaics to biophotonics. However, it remains a daunting challenge to significantly intensify upconversion luminescence in small nanoparticles with a simple structure. Herein, we report the amplification of photon upconversion through engineering interfacial density of states between the core and the shell layer in sub-10 nm colloidal rare-earth ions doped fluoride nanocrystals. Through tuning of the metal cations in the shell layer of alkaline-earth-based core/shell nanoparticles, both the interfacial phonon frequency and the density of state are evidently decreased, resulting in the luminescence intensification of up to 8224 times. The generality of this upconversion enhancement strategy has been verified through expansion of this approach to alkali-based core/shell nanoparticles. The engineering of photon density of state in such core/shell nanoparticles enables dynamic display and high-level security information storage.

Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Lanthanide ions with thermally coupled levels have been widely used for ratiometric temperature sensing. However, these systems suffer from low relative temperature sensitivity and poor luminescence signal discriminability. Herein, the concept of indirectly thermally coupled levels is introduced and employed to actualize high performance temperature sensing. By means of the temperature-dependent phonon-assisted non-radiative relaxation, the 4I13/2 excited state (with infrared emission) of Er3+ can be indirectly thermally coupled with the 4S3/2 excited state (with visible emission) under 808 nm or 980 nm excitation. This is experimentally realized in specially designed NaErF4:10Yb@NaYF4 nanocrystals, and the corresponding ratiometric nanothermometer shows excellent luminescence thermal sensing performance with a maximum relative sensitivity value up to 3.76% K−1 at 295 K.

Heterometallic cluster-organic frameworks with fascinating architectures and multi-functionality have the potential to be applied in various fields. However, in comparison with p–d, d–d, and d–f heterometallic cluster-organic frameworks, p–f heterometallic cluster-organic frameworks are far less explored even though they possess multiple merits. Herein, two novel isomorphic 4p–4f heterometallic cluster-organic frameworks based on high-nuclear [Ln11Ge12] (Ln = Pr, L1 and Nd, L2) second building units have been successfully synthesized via a hydrothermal approach by using bis(carboxyethylgermanium) sesquioxide (H2E2Ge2O3, E = –CH2CH2COO–). The [Ln11Ge12] cluster is constructed with two Ln-capped Ge6-rings sandwiching a gear-like [Ln9] unit. The as-prepared 4p–4f heterometallic [Ln11Ge12] cluster-organic frameworks possess two-dimensional (2D) layered structures. Moreover, the property study reveals the selective and sensitive luminescence sensing of Fe3+ with L1, exhibiting its promising application in environmental monitoring.

Multicolor luminescent nanoparticles (NPs) show several potential emerging applications. In this work, we provide a new route that integrates the afterglow and upconversion (UC) that originate in a single activator to achieve color variations without the modulation of any other parameters. The Er3+ ions in Na3HfF7:Yb/Er NPs exhibit bright green afterglow upon X-ray irradiation and single-band red UC under 980 nm laser excitation, which are attributed to the significantly different electron population pathways. The UC intensity is stable and the afterglow decreases gradually over time, thus the output color is clearly changed from green to red naturally via illuminating the pre-X-ray-irradiated NPs with a 980 nm laser. Furthermore, the fine emission profiles of Er3+, Ho3+ and Tm3+ are achieved upon X-ray irradiation. Our results develop a new approach for time-dependent dynamic color displays and a simple route to revealing the electronic fine structures of lanthanide activators at room temperature.

Fluorescence intensity ratio-based temperature sensing with a self-referencing characteristic is highly demanded for reliable and accurate sensing. Although enormous efforts have been devoted to explore high-performance luminescent temperature probes, it remains a daunting challenge to achieve highly relative sensitivity which determines temperature resolution. Herein, we employ a novel strategy to achieve temperature probes with ultrahigh relative sensitivity through integrating both positive and negative thermal quenching effect into a hydrogel. Specifically, Er3+ ions show evidently a positive thermal quenching effect in Yb/Er:NaYF4@NaYF4 nanocrystals while Nd3+ and Tm3+ ions in a Yb2W3O12 bulk exhibit prominently a negative thermal quenching effect. With elevating temperature from 313 to 553 K, the fluorescence intensity ratio of Er (540 nm) to Nd (799 nm) and Tm (796 nm) to Er (540 nm) is significantly decreased about 1654 times and increased about 14,422 times, respectively. The maximum relative sensitivity of 15.3% K-1 at 553 K and 23.84% K-1 at 380 K are achieved. The strategy developed in this work sheds light on highly sensitive probes using lanthanide ion-doped materials.

Luminescence modification of lanthanide ions has attracted great attention due to its applications in sensing, colorful display, information transmission and anti-counterfeiting. Traditional methods of tuning fluorescence typically employ tuning compositions that are not conducive to the development of multi-environment detection and anti-counterfeiting. In this study, lanthanide ions doped ferroelectric nanocomposite was exploited with external stimuli. The upconversion luminescence modification was preformed via both the thermal and electric fields. The anti-thermal quenching phenomenon was observed in the prepared nano-composite, which could effectively enhance the upconversion luminescence of lanthanide ions. Based on the electromechanical softness of the ferroelectric lattice, exceptional luminescence modification was realized through electric polarization. The luminescence modifications by thermal and electric fields exhibited excellent reversibility and non-volatility. These results provide unique insights into the development of integrated stimulus responsive smart devices, colorful display and advanced multi-mode sensing materials.

A novel dual-emitting Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors with ultrahigh-sensitive optical temperature sensing are prepared by a conventional solid-state method. The Eu2+/Eu3+ co-activated Ca8ZrMg(PO4)6(SiO4) phosphors exhibit efficient dual-mode emissions with an intense, broad blue emission peaked at 414 nm and a relative bright red-emitting centered at 614 nm under 297 nm UV-light excitation, respectively. Furthermore, the fluorescence intensity ratio (FIR) technology is applied to analyse the optical temperature sensing performance of Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors. Based on different thermal quenching behavior of Eu2+ and Eu3+ dual-emitting centers, linear temperature-dependent FIR between Eu2+ and Eu3+ is obtained. The maximal absolute sensitivity reaches as high as 5.94% K−1, which is superior to that for the other luminescent temperature sensing materials reported previously. Analyses of the temperature-dependent photoluminescence spectra and configurational coordinate diagrams for Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors indicate that the temperature-sensitive variation in FIR of Eu2+ to Eu3+ is originated from the difference in thermal quenching activation energy for 5d→4f transition of Eu2+ and 5D0→7FJ (J = 1, 2, 4) transitions of Eu3+. These results reveal that the Ca8ZrMg(PO4)6(SiO4): (Eu3+, Eu2+) phosphors show glorious potential in high temperature optical thermometry.

Eu2+ activated aluminate Sr4Al14O25 with dual-emitting centers were prepared via a solid-state method in a reductive atmosphere. Photoluminescence emission (PL) and excitation (PLE) spectra of phosphor along with the lifetimes were characterized, which confirm the 5d→4f energy transition behavior of Eu2+ between 400 nm and 490 nm emission. The fluorescence intensity ratio of I490 and I400 in the phosphors exhibits remarkable temperature dependence, owing to the diverse thermal quenching behaviors of Eu2+ emission centers. Using the phosphors to perform thermometry, excellent temperature sensitivity is achieved in the temperature range of 293–423 K. The maximum absolute and relative sensitivity are 0.004 K-1 and 0.624% at 373 K, respectively. In particular, the dual-site luminescence of Eu2+ ions can be used as the reference signal and the temperature signal of the fluorescence temperature sensor respectively. It will be helpful to develop a new self-reference optical temperature measurement technology with excellent performance.

The emission properties of lanthanide ions have been extensively investigated for their interesting physical processes and enormous applications. Conventional strategies have been used to modify luminescence properties such as temperature, pressure, and modifying components. However, the traditional methods are volatile and irreversible, which is unconducive for some optoelectronic applications. In this article, the electromechanical softness of the ferroelectric lattice is employed, which makes the strong coupling relationship between the electric field and the photonic properties of lanthanide ions. The emission intensity of the Tm3+:3H4-4H6 and 3F4-4H6 transitions was exceptionally enhanced by 2.6 and 3.2 times via ferroelectric polarization, respectively. Meanwhile, the luminescence response presents excellent reversibility and nonvolatility. This study provides a unique proposal for designing highly integrated stimuli-responsive photonic materials toward a variety of applications.

Lanthanide ion doped ferroelectric oxides have unique ferroelectric and luminescence properties, which show great promise for future optoelectronic applications. Moreover, it is of great interest that the luminescence of ferroelectric materials can be effectively modulated by an external electric field. In this work, Nd3+ doped ferroelectric nanocomposites with near-infrared emission have been developed to study their optoelectronic properties and reversible tuning. At room temperature, the near-infrared emission has been enhanced over 4.6 times and the intensity can be controllably modulated by tuning the electric field. The mechanism behind the enhancement and reversible modulation has been investigated for designing luminescence memory or optoelectronic sensors. This work suggests a way for not only studying the luminescence properties of optical materials via polarization engineering, but also for potentially developing multifunctional materials for optoelectronic applications.

It is common that thermal quenching in luminescent materials inevitably occurs with an elevation in temperature. Herein, an inverse thermal quenching effect in lanthanide-doped upconversion nanocrystals was reported. Specifically, defects with an appropriate energy state were designed in Yb/Er (Ho, Tm) doped Na3ZrF7 nanocrystals to actualize a thermal-induced enhancement in luminescent intensity. Owing to this special temperature dependent optical property, our results reveal that these kinds of materials are very suitable for high security anti-counterfeiting applications.

Based on the inner filter effect, a luminescent Zn(ii)/Na(i) metal-organic framework (MOF) {[Zn2Na(L)(HL)2(H2O)2][OAc]·2H2O}n (1, H2L = 5-methyl-1,3-benzenedicarboxylic acid) with excellent stability was constructed for the fluorescence detection of Cu2+ ions. MOF 1 holds a 3D cationic framework in which [(OAc)2(H2O)2]n2n- anions are embedded into its 1D channels. Abundant hydrogen-bonding and π-π interactions in the MOF facilitate electron transfer from ligand-to-metal, resulting in a good luminescence peak at 412 nm and an efficient fluorescence quenching of MOF 1 in the presence of Cu2+ ions, due to the inner filter effect. The interactions between the Cu2+ ions and the OAc- anion in the channel endowed the Cu2+ ions with facile access to be adsorbed, and afforded the selective quenching of fluorescence. The MOF particles are well dispersed in water and the Cu2+ ions are pre-concentrated by adsorption, thus facilitating the determination of Cu2+ ions with a detection limit down to 0.65 μM. Our work thus paves a way for developing MOFs as an appealing platform to construct materials for environmental applications.

Luminescent materials with negative thermal quenching effects show superior potentials in temperature sensing and anti-counterfeiting fields. Normally, smaller nanocrystals (NCs) with higher surface-to-volume ratios are used to achieve larger thermal-induced intensification of upconversion (UC) emission intensity. Herein, confining sensitizers and activators to the shell layer with two-dimensional space and introducing defect energy levels via doping low-valence ions are simultaneously applied to enhance the negative thermal quenching effect. By increasing the temperature from 293 K to 413 K, the integral UC emission intensity of 20Yb/2Er:NaGdF4 increases only by ∼2.2 times, whereas that of NaGdF4@20Ca/20Yb/2Er:NaGdF4 core–shell NCs with a similar particle size increases by ∼10.9 times.

All inorganic CsPbX3 (X = Cl, Br, I) perovskite quantum dots have attracted extreme attention due to their excellent optical performance. Unfortunately, heavy usage of the toxic Pb element is still a serious problem that needs to be solved. In the present work, Mn-doped CsPbCl3 nanocrystals are successfully prepared via a facile solvothermal reaction for the first time. A high Cs-to-Pb feeding ratio is necessary to achieve pure cubic perovskite phase and the incorporation of Mn dopants into the CsPbCl3 host is highly related to the Mn-to-Pb feeding ratio. Importantly, it is demonstrated that Mn-doped CsPbCl3 NCs synthesized by the solvothermal method have better stability than those prepared by traditional hot injection. To finely adjust the bandgap of CsPbCl3 NCs, Cl-to-Br anion exchange is used to fabricate Mn-doped CsPb(Cl/Br)3 NCs with tunable multi-color luminescence. Finally, the as-prepared Mn-doped CsPb(Cl/Br)3 products are demonstrated to be applicable as color converters for constructing white light-emitting diodes and optical thermometric medium for accurate temperature sensing.

Successful development of all-inorganic CsPbX3 (X = Cl, Br, or I) perovskite quantum dots (PQDs) has been witnessed due to their unique optical and electrical properties. However, the heavy usage of Pb element in PQDs has limited the commercial application of these PQDs, and the preparation of low-Pb or Pb-free PQDs is imperative. In this study, we report room-temperature reverse synthesis of CsPbxMn1−xCl3 PDQs from CsMnCl3 precursor nanocrystals through cation exchange. Interestingly, two-step phase transformation processes from hexagonal CsMnCl3 to rhombohedral Cs4PbxMn1−xCl6 and finally to cubic CsPbxMn1−xCl3 are evidenced. With an increase in the reaction time, Mn2+ ions in the PQD lattice are gradually replaced by Pb2+ ions. Notably, Mn2+ d → d broadband luminescence is not detected for the Cs4PbxMn1−xCl6 product, but it is intense for the CsPbxMn1−xCl3 sample owing to efficient energy transfer from CsPbCl3 to Mn2+. Moreover, it is found that the introduction of Br− into the reaction system will prohibit the complete phase transformation from rhombohedral Cs4PbxMn1−x(Cl/Br)6 to cubic CsPbxMn1−x(Cl/Br)3. By controlling the ratio between the CsMnCl3 precursor and PbBr2, tunable luminescence is easily achieved due to the combined emissions from both CsPb(Cl/Br)3 PQDs and Mn2+-emitting centers.

In order to study the optical temperature sensing characteristics of phosphors with dual emission centers, a series of La2MgGeO6: Bi3+, Mn4+ phosphors were prepared by solid phase method at high temperature. Due to the different thermal responses of Bi3+ and Mn4+ ions, the fluorescence intensity ratio between the double emission centers is expected to be an effective method for temperature sensing. The structural phase and luminescence properties of the samples were characterized by X-ray powder diffraction, field emission scanning electron microscopy, ultraviolet spectrophotometer and fluorescence spectrometer. According to the structure of La2MgGeO6 host, it can be seen that Bi3+ ion can replace La3+ ion and Mn4+ ion can replace Ge4+ ion because the valence state of ions are the same and the ion radius is close. Through the excitation of ultraviolet light, La2MgGeO6: Bi3+, Mn4+ present two emission bands, which correspond to the Bi3+ ions 3P1 → 1S0 transition (emitting blue light) and Mn4+ ions 2Eg → 4A2g transition (emitting red light) respectively. Moreover, there is energy transfer from Bi3+ ions to Mn4+ ions. Based on the different temperature responses of Bi3+ blue emission and Mn4+ red emission, their fluorescence intensity ratio was used to discuss the temperature measurement characteristics. The absolute sensitivity and relative sensitivity of La2MgGeO6: Bi3+, Mn4+ phosphors reached the maximum value of 1.419% K−1 at 473 K and 3.027% K−1 at 383 K in the temperature range of 293–473 K. Therefore, La2MgGeO6: Bi3+, Mn4+ phosphors are excellent materials for optical temperature measurement.

A series of Er3+ doped and Er3+/Yb3+ codoped SrTiO3 nanocubes with varying dopant concentrations have been successfully synthesized by a facile hydrothermal method. The doping effects on phase purity, morphology and microstructure of samples were identified by power X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that SrTiO3 nanocubes have a typical perovskite structure with the edge length ranging 20–50 nm. The Er3+ and Yb3+ ions were successfully doped into the crystal lattice of SrTiO3, but did not alter crystal structure of SrTiO3. The photon up-conversion (UC) photoluminescence (PL) measurements indicated that the intense green light emission of Er3+ ions around 525 nm, 550 nm and red light emission centered at 670 nm in UC processes populated by 980 nm laser excitation have been achieved in SrTiO3 nanocubes. Moreover, the PL intensity of Er3+-doped SrTiO3 nanocubes was greatly enhanced while introducing the Yb3+ to the crystal structure, especially the red emission. The mechanisms for these emissions probably due to the excited state absorption (ESA) and energy transfer (ET) process. Er3+/Yb3+-codoped single-crystal perovskite SrTiO3 nanocubes could be interesting objects for applications in mechanical−electrical luminescence such as electric field modulation luminescence and mechanoluminescence.

The ultrasmall Yb/Er: CaF 2 NCs are chosen as an example to certify the upconversion emission intensity can be greatly enhanced through combining various approaches together, including doping Na + ions to promote the growth the particle size and tailor the crystal-field environment of the emitters, control shell thickness to lower the non-radiative decay and tune Yb 3+ concentration in the shell to enhance the absorption of the excitation energy. In comparison with Na + -free 20Yb/2Er: CaF 2 NCs (~ 2 nm), the upconversion luminescence of 20Yb/2Er: CaF 2 @10Yb: CaF 2 NCs (~ 9 nm) containing ~ 0.5 mmol Na + ions in the core and 10% Yb 3+ in the shell with 5 nm thickness intensifies for about 95 times.

Novel blue LED excitable Ce3+-doped alkaline-earth sulfide nanocrystals are exploited for selective and sensitive Fe3+ ions sensing in this work. The detection limit is calculated to be as low as 92.5 nM, which is better than most previous ultra-violet light excited fluorescence probes. The decreased radiative probability of the Ce3+: 5d by the NC surface environmental variation activates the sensing capability.

Up-convertion (UC) perovskite Er3+-doped PbTiO3 (Er-PTO) nanoparticles with green and red emissions were synthesized via the hydrothermal method. The UC properties were manipulated by adjusting the concentration of Er3+ ions dopant. The green emission intensity was decreased as the doping concentration increased from 1% to 4% (mole fraction), whereas the red emission intensity was increased. The influences of Er3+ ions on the temperature-sensing performance were further investigated. The results demonstrated that Er-PTO nanoparticles with doping 1% Er3+ ions possessed a sensitivity of 3.1 × 10-3 K−1 at 475 K, presenting a high potential in optical heating devices.

A series of environment friendly Eu/PHB fluorescent films through doped the Eu-complex precursor Eu(TTA) 2 (Tpy-OCH 3 )(2H 2 O) into polymer matrices poly-β-hydroxybutyrate (PHB) with doping percentage at 1, 3, 5, and 7 (mass) were designed, fabricated and characterized. TGA and PL results indicated the Eu-complex precursor was immobilized in PHB matrix through the interaction between the Eu-complex. DSC results indicated the crystallinity of Eu/PHB films decreased with the increase of Eu-complex doping percentage. The emission spectra of the Eu-complex and Eu/PHB films recorded at room temperature exhibited the characteristic bands arising from the 5 D 0 / 7 F J . The fact that the quantum efficiencies ( η ) of the doped film increased significantly revealed that the PHB matrix acts as an efficient co-sensitizer for Eu 3+ ions luminescent center and therefore enhances the quantum efficiency of the emitter 5 D 0 level. In particular, all Eu/PHB films can be excited by visible light (410 nm), and also showed good photoluminescent properties. So the new Eu/PHB fluorescent films showed considerable promise for polymer light-emitting diode, active polymer optical fiber and biomedical analysis applications.

A new coordination polymer, [Cu(L)(bpmb)]n (I) (L = benzene-1,2-dicarboxylic acid, bpmb = 1,2-bis(pyridine-3-ylmethoxy)benzene), has been hydrothermally synthesized and characterized by single X-ray diffraction, IR, element analysis, and thermal analysis. The compound I shows a two-dimensional corrugated sheet with 4462 topology. In addition, the luminescent property of I is investigated.

A novel efficient antenna Eu-complex Eu(TTA)2Tpy-OCH3·2H2O, based on the terpyridyl derivative 4′-(4-methoxyphenyl)-2,2′:6′,2′′-terpyridine(Tpy-OCH3) as the ancillary ligand, has been synthesized, structurally characterized, and its photophysical properties have been examined. Upon irradiation at the ligand-centered band in the range of 200–450 nm, the new Eu-complex displays bright red luminescence, irrespective of the medium. A Sparkle/RM1 calculation was utilized for predicting the ground-state geometries of this complex. Theoretical Judd–Ofelt and photoluminescence parameters, including quantum efficiency, as predicted from this model are in good agreement with the experimental values, proving the efficiency of this theoretical approach as implemented in the LUMPAC software (http://lumpac.pro.br). The kinetic scheme for modelling energy transfer processes shows that the main donor state is the ligand triplet state and that energy transfer occurs on both the 5D1 (20.7%) and 5D0 (79.3%) levels. As an integral part of this work, the synthesis, characterization, and luminescence properties of poly(vinyl butyral) (PVB) polymer films doped with the Eu-complex are also reported. After the Eu-complex Eu(TTA)2Tpy-OCH3·2H2O was doped into the PVB matrix to form the films, the PVB polymer matrix, acting as a co-sensitizer for Eu3+ ions, enhances the luminescence lifetimes and quantum efficiencies of the complex in comparison with its precursor complex. The new luminescent Eu/PVB films therefore show considerable promise for polymer light-emitting diode and active polymer optical fiber applications. To the best of our knowledge, this is the first report which studies in detail the photophysical properties of doped europium fluorescent films based on PVB as the polymer matrix.

Lanthanide (Ln3+)-doped nanoparticles that produce strong red upconversion (UC) luminescence are desirable for biological applications. For nanoparticles, modification of their electronic properties and stabilization of their crystallographic phase are crucial for tuning their luminescence behaviors. Here, Yb3+–Er3+ doped Gd2O3 nanoparticles have been synthesized by calcining Gd2O2S in nitrogen (O2-free) and ambient air (∼21% O2), respectively. Various approaches including X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and thermo-gravimetric and differential thermal analyses (TG-DTA) were used to characterize the structure, morphology and phase formation mechanism of the nanoparticles. Upconversion luminescence properties were investigated by emission intensity vs. excitation power (double logarithmic relationship) and temperature dependent emission spectroscopy. The different splitting transition probabilities of the cubic and/or monoclinic phase, the probability of multiphonon relaxations and cross relaxations between Er3+ ions are responsible for the efficient red emission in the cubic Gd2O3 nanoparticles. More importantly, the lower phonon energy of the pure cubic sample has good thermal stability in the current detectable range of 20–100 °C. These results imply that the cubic Gd2O3 upconversion nanoparticles may have multiplexing functionality in bio-imaging.

The strong 1830 nm emission is realized in Yb/Tm:NaYF 4 @Yb:NaYF 4 core/shell nanocrystals for the first time. The optimal Tm 3+ concentration, shell thickness and composition respectively are 2 mol%, 6.5 nm and inert NaYF 4 . In comparison with Yb/Tm:NaYF 4 nanocrystals, the luminescence intensity of Yb/Tm:NaYF 4 @NaYF 4 core/shell nanocrystals enhances about 160 times.

Self-assembly of Cd(II) ions with five positional isomeric flexible bipyridyl benzene and 2,2′-azodibenzoic acid ligands yielded five interesting coordination polymers: [Cd2L2(3-pbpmb)3]n (1), [Cd2L2(2-pbpmb)]n (2), {[CdL(4-mbpmb)2]·MeOH}n (3), {[Cd2L2(3-mbpmb)3]·2.5H2O}n (4) and [Cd2Cl2L(3-obpmb)2]n (5) where H2L = 2,2′-azodibenzoic acid, 3-pbpmb = 1,4-bis(pyridine-3-ylmethoxy)benzene, 2-pbpmb = 1,4-bis(pyridine-2-ylmethoxy)benzene, 4-mbpmb = 1,3-bis(pyridine-4-ylmethoxy)benzene, 3-mbpmb = 1,3-bis(pyridine-3-ylmethoxy)benzene and 3-obpmb = 1,2-bis(pyridine-3-ylmethoxy)benzene. Their structures have been determined by single-crystal X-ray diffraction analyses, elemental analyses, IR spectroscopy, powder X-ray diffraction (PXRD) and thermogravimetric analyses (TGA). Compound 1 has a 3D architecture constructed by 1D ladder-like [Cd4(3-pbpmb)4]n chains as well as L linkers and displays an interesting 5-connected net with a 4664 topology. Compound 2 comprises a 3D framework built from 2D wrinkled [Cd2L4]n networks and 2-pbpmb bridges with a 6-connected pcu net. Compound 3 bears a 2D network based on [Cd2(4-mbpmb)2] building units and 1D [CdL]n chains. Compound 4 features a 2D network in which the helical [Cd(3-mbpmb)]n chains are alternately arranged in a right- and left-handed sequence. Compound 5 exhibits a 2D network constructed by 1D [Cd2Cl2(3-obpmb)2]n chains and L linkers. The results reveal that the diverse coordination networks of 1–5 can be adjusted by the positional isomeric effect of flexible bipyridyl benzene building blocks. Moreover, the luminescence properties of compounds 1–5 in the solid state have also been investigated.

After coating 20 Yb/2 Er:NaGdF4 core nanocrystals with a NaYbF4 shell, upconversion emission of the rare earth ions weakens. So far, the exact reason for this phenomenon is still unclear due to lack of the direct evidence. In this report, a core@shell@shell sandwich-like structure is designed and fabricated to investigate this phenomenon. We find that high Yb(3+) concentration in the shell has mainly two adverse impacts: it promotes not only the deleterious back energy transfer from Er(3+) in the core to Yb(3+) in the shell but also the energy transfer from Yb(3+) in the core to Yb(3+) in the shell. To obtain nanocrystals with high upconversion efficency, appropriate Yb(3+) concentration should be introduced into the shell or the transition layer.

A new coordination polymer, namely [Zn(Hnbdc)2(bpe)]n (1) (H2nbdc = 3-nitrobenzene-1,2-dicarboxylic acid and bpe = 1,2-bi(4-pyridyl)ethylene), has been hydrothermally synthesized and characterized preliminarily by elemental analysis, infrared spectroscopy, thermal analysis, and X-ray diffractions. Single crystal X-ray diffraction showed that compound 1 possesses a ladder-like topology structure featuring carboxyl-bridged dinuclear Zn(II) spaced by parallel bpe coligand pairs and has the capacity of undergoing a 100% photochemical [2 + 2] cycloaddition reaction to transform into compound [Zn(Hnbdc)2(rctt-tpcb)]n (2) in a single-crystal to single-crystal form. In addition, the fluorescent property of 1 was also investigated.

Hydrothermal reactions of Cd(OAc)2 · 2H2O with 2,2′-azodibenzoic acid (H2L) and three N-donor ancillary ligands in MeOH/H2O at 120 °C gave rise to three cadmium(II) coordination polymers [CdL(bpy)]n (1), {[Cd4L4(bpe)(H2O)2] · 2H2O}n (2) and [CdL(bpp)]n (3) [bpy = 4,4′-bipyridine, bpe = 1,2-bis(4-pyridyl)ethylene, bpp = 1,3-bis(4-pyridyl)propane]. Structural analysis reveals that compound 1 possesses a novel three-fold interpenetrating diamondoid framework constructed by linking Cd centers with L and pillared bpy ligands. Compound 2 comprises a 3D network with a rare Schlafli symbol of (446581)(4462), the 3D structure is built from 2D [CdL2]n nets and pillared bpe ligands. Compound 3 exhibits the same 66 topology with that of 1. Such a 3D architecture contains 1D helical [Cd(bpp)]n chains and [CdL]n chains along the a axis and b axis, respectively. The structural differences among 1–3 indicate that the N-donor ancillary ligands have significant effects on the formation of the final architectures. Photoluminescent properties of 1–3 in solid state were also investigated.

Solvothermal reactions of Cd(OAc)2·2H2O with 3,3′-azodibenzoic acid (H2L) in N,N′-dimethylformamide (DMF) or DMF/MeOH at 100 °C or 120 °C gave rise to three cadmium(II) coordination polymers {[CdL(DMF)2]·0.5DMF}n (1), [CdL(DMF)(MeOH)]n (2) and {[Cd3L3(DMF)4]·0.5DMF}n (3). Complexes 1–3 were characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffraction. In 1–3, dinuclear [Cd2L4(DMF)4] (1) or [Cd2L4(DMF)2(MeOH)2] (2) unit and trinuclear [Cd3L6(DMF)4] (3) unit acts as a four-connecting node to link its equivalent ones via sharing L ligands to form 2D layers, which are further connected through the C−H⋯π (1) or hydrogen-bonding interactions (2–3) to afford 3D networks with the 41263 topology. The network of 1 allows other one to be penetrated for the formation of twofold interpenetrating pcu net. The formation of 1–3 provided an interesting insight into solvent and temperature effects on the construction of coordination polymers under solvothermal conditions. In addition, the photoluminescent properties of 1–3 in solid state at ambient temperature were also investigated.

Four [Cu2I2]- or [Cu4I4]-based coordination polymers, [CuI(bpp)]n (1), {[Cu3I3(bpp)3]·2aniline·MeCN}n (2), {[Cu2I2(bpp)2]·2aniline}n (3), and [Cu4I4(bpp)2]n (4), were prepared by solvothermal reactions of CuI or Cu2(OH)2CO3 with 1,3-bis(4-pyridyl)propane (bpp) in different solvent systems. The preparation of 2 or 3 is involved in the in situ formation of aniline molecules and the reduction of Cu(II) to Cu(I). These compounds were characterized by elemental analysis, IR, and single crystal X-ray diffraction. Compound 1 consists of [Cu2I2] dimeric cores that link the neighboring ones via bpp bridges to form a one-dimensional double-bridged polymeric chain. Compound 2 or 3 has a similar chain structure in which the shape and size of the [Cu2I2(bpp)2]2 cavities that are occupied by MeCN/aniline or aniline solvent molecules are different from those of 1. Compound 4 has an intriguing two-dimensional 4-fold interpenetrated network in which each cubanelike [Cu4I4] core acts as a rare “seesaw”-shaped four-connecti...

A novel Cd(II)/4-pya coordination polymer {[Cd(μ-Cl)(4-pya)(H2O)]2 · 4H2O}∞ (1) (4-pya = trans-4-pyridylacrylate) was synthesized and structurally characterized. Single-crystal X-ray diffraction revealed that 1 consists of a 2D (4, 4) network constructed from the 4-pya bridging ligand and the dimeric [Cd(μ-Cl)]2 cores, in which each six-coordinated Cd(II) ion adopts an octahedral coordination geometry. Each 2D layer is further stacked along the a axis through hydrogen bonding interactions to afford a 3D hydrogen-bound network. An infinite water chain is generated via hydrogen bonds into each resulting 1D channel. The luminescent properties of 1 in the solid state were investigated.

In most of the reports on nanocrystal (NC) luminescent, the power depedence of luminescent intensity is studied using a continuous-wave laser with low power density, and the slopes of those different emission bands keep unchanged. In this paper, the up/down conversion of monodisperse Yb/Er: NaGdF4@Yb: NaGdF4@Yb: NaNdF4 NCs under the excitation of 800[Formula: see text]nm femtosecond laser was detected simultaneously by a home-built optical measurement setup. The power-dependent optical properties under the excitation of femtosecond laser are quite different from the normal situation, which is due to their high peak power and energy transfer processes: Nd[Formula: see text].

Electrochemically induced Fenton (electro-Fenton) reaction was used for efficient and controllable preparation of hydroxyl radicals, leading to the generation of luminescent quantum dots through etching of as-exfoliated MoS2 nanosheets. Morphologic changes of MoS2 nanosheets during the electro-Fenton reaction were monitored using transmission electron microscopy, showing that etching of MoS2 nanosheets induced by hydroxyl radicals resulted in rapid homogeneous fracturing of the sheets into small dots via a transition of nanoporous morphology. The as-generated dots with vertical dimensional thickness of ca. 0.7 nm and plane size of ca. 5 nm were demonstrated to be MoS2 quantum dots (MoS2-QDs), and their photoluminescence properties were explored based on quantum confinement, edge effect, and intrinsic characteristics. Moreover, the degree of etching and the concomitant porosity of MoS2 nanosheets could be conveniently tuned via the electro-Fenton reaction time, resulting in a new morphology of nanoporous MoS2 nanosheets, with potential new applications in various significant areas.

Upon introducing Ca(2+) dopants into the grain lattices by substituting Gd(3+) ions, irregular Yb/Er:NaGdF4 nanocrystals prepared through a simple solvothermal route convert into highly uniform nanorods. Meanwhile, their upconversion luminescence intensifies by about 200 times, probably due to a modification of the crystal structure of NaGdF4 and an improvement in the crystallinity of the nanophase.

A series of Er(3+)-doped (1 - x)CaF(2)-xYbF(3) (0 ≤ x ≤ 0.6) disordered solid-solution nanocrystals with various mean sizes were successfully prepared by a facile solvothermal route. Interestingly, abnormal size-dependent upconversion emissions were demonstrated in these nanocrystals for the first time. With increasing grain size, an obvious enhancement of red to green emission ratio was observed in the Er(3+) (2 mol%): 0.4CaF(2)-0.6YbF(3) nanocrystals, which is the opposite of the routine size-dependent upconversion emission behavior reported previously. Taking Eu(3+) ions as a structural probe, we investigated the influence of a disordered solid-solution structure on Ln(3+) luminescence, and proposed that Ln(3+) clusters formed in the host should play a key role to induce this unusual size-dependent upconversion emission phenomenon. As a consequence, multi-colors such as green, yellow, and red upconversion emissions can be easily realized by appropriately modifying the Yb(3+) content in the Er(3+)-doped (1 - x)CaF(2)-xYbF(3) nanocrystals. The reported results will deepen the understanding of size effects on the lanthanide upconversion in nanocrystals.

Dissolving CuBr and 2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)pyridine (bdmpp) in MeCN followed by a solvothermal treatment afforded an unique mixed-valence Cu(I,II) cyanide coordination polymer [Cu(II)Cu(I)2(µ-Br)2(µ-CN)2(bdmpp)]n (1). Comparative reactions using CuCN and bdmpp under the same conditions gave rise to a different mixed-valence Cu(I,II) cyanide polymer [Cu(II)Cu(I)3(µ-CN)5(bdmpp)]n (2). Both reactions are involved in partial oxidation of Cu(I) into Cu(II) via O2 in open air while in the case of 1, the cyanide may be generated in situ from the C–C cleavage of acetonitrile under solvothermal conditions. 1 consists of a 2D (6,3) layer network in which the [Cu(I)8{Cu(II)(bdmpp)}4(µ-Br)8(µ-CN)7]n double chains are interconnected by a pair of µ-CN bridges. 2 shows a 2D (6,3) folded network in which the [Cu(I)6{Cu(II)(µ-CN)(bdmpp)}2(µ-CN)7]n double chains are inter-linked by a pair of µ-CN bridges. The luminescent properties of 1 and 2 in solid state at ambient temperature were also investigated.