Luminescent Metal-organic Framework Research Articles

Restriction of Intramolecular Vibration in Aggregation‐Induced Emission Luminogens: Applications in Multifunctional Luminescent Metal–Organic Frameworks

AbstractButterfly‐like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation‐induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV‐type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one‐step catalyst‐free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal–organic frameworks (MOFs) due to their built‐in pyrazine coordination sites. OAP‐based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light‐emitting devices. This work builds on RIV‐type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.

Restriction of Intramolecular Vibration in Aggregation-Induced Emission Luminogens: Applications in Multifunctional Luminescent Metal-Organic Frameworks.

Butterfly-like molecules of oxacalix[2]arene[2]pyrazine (OAP) are reported, which exhibit the typical characteristics of aggregation-induced emission (AIE) via the restriction of intramolecular vibration (RIV) mechanism. Unlike any of the reported RIV-type AIE molecules, the synthetic procedures of which are complicated and have associated high costs, OAP AIEgens can be synthesized in a facile manner by a one-step catalyst-free reaction using commercially available materials. Notably, OAP AIEgens are ideal ligands for constructing metal-organic frameworks (MOFs) due to their built-in pyrazine coordination sites. OAP-based MOFs exhibit multiple potential applications in reversible gas response, encrypted information storage, and construction of white light-emitting devices. This work builds on RIV-type AIEgens, offers additional selections of bridging ligands for constructing luminescent MOFs and provides a visualized prototype to understand the effect of the RIV process on the luminescence properties of MOFs.

A stable lanthanum-based metal-organic framework as fluorescent sensor for detecting TNP and Fe3+ with hyper-sensitivity and ultra-selectivity

A new Lanthanum-based luminescent metal–organic framework, {[La(H2O)4(HL)]·H2O} (1), has been successfully synthesized by employing 3,3′,5,5′-azodioxybenzenetetracarboxylic acid (H4L) as a rigid organic linker through the solvothermal reactions. 1 exhibits a two-dimensional (2D) layered structure and a three-dimensional (3D) supramolecular structure is formed by hydrogen bonds between the layers. Stability studies indicate that 1 has good chemical stability and thermostability. Meanwhile, the Ksv values for TNP is 4.61 × 104 M−1 with the LOD of 4.13 × 10-6 M and the Ksv value for Fe3+ is 1.22 × 104 M−1 with the LOD of 1.72 × 10-5 M, respectively, which demonstrated that 1 exhibits high sensitivity and excellent selectivity for the detection of TNP and Fe3+via fluorescence quenching. Significantly, 1 shows high regenerability after five recycling progress for sensing Fe3+. The possible mechanisms associated with the luminescent quenching are discussed in detail through some relevant experiments and tests, as well as the DFT calculations. Based on the above excellent properties of 1, it will have extremely potential to be used as a dual functional sensor for both detecting TNP and Fe3+ in aqueous solution, simultaneously.

(4,5,8)-Connected Cationic Coordination Polymer Material as Explosive Chemosensor Based on the in Situ Generated AIE Tetrazolyl-Tetraphenylethylene Derivative.

A multidentate tetrazole molecule based on a TPE core, tetrakis[4-(1H-tetrazol-5-yl)phenyl]ethylene (H4ttpe) with combined advantages of two functional groups, was synthesized by cycloaddition reaction of the corresponding organic benzonitrile derivative and azide salt. Coordination self-assembly of the in situ formed aggregation-induced emission polytetrazole luminogen with cadmium(II) ion produces an unprecedented tetrazolyl-TPE-based microporous cationic metal-organic framework (MOF) with an unusual (4,5,8T14)-connected net of {[Cd4(H4ttpe)2Cl5]·(N3)3}, in which the H4ttpe serves as the first undeprotonated tetrazole ligand of octa-coordinating bridging mode. We investigate, for the first time, the utilization of the luminescent MOF containing a TPE core decorated with tetrazolyl terminals for explosive detection based on the change in fluorescence intensity, which shows high selectivity and efficiency in fluorescence quenching toward TNP detection in water solution.

Engineering Near-Infrared-Excitable Metal-Organic Framework for Tumor Microenvironment Responsive Therapy.

Luminescent metal-organic frameworks (MOFs), which incorporate some guest luminescent molecules/ions into MOFs, have attracted extensive attention because of their exceptional optical properties. However, traditional luminescent MOFs are mainly responsive to ultraviolet (UV) or visible light, which has limited their bioapplications due to the restrained tissue penetration depths. In this study, we have constructed a diagnostic nanoplatform UCNP@MOF consisting of upconverting metal-organic frameworks, which combine the photo-upconverting characteristics of the upconversion nanoparticles (UCNPs) with the unique physicochemical properties of Al-MOFs. Specifically, the core-shell structured UCNP@MOF nanocomposites were prepared by poly(vinylpyrrolidone) (PVP)-regulated nucleation of Al-MOF layer on the UCNP surface. When excited by a 980 nm laser light, the green signal released from UCNPs can trigger the photosensitive Al-MOFs to produce a large amount of singlet oxygen (1O2) for photodynamic therapy (PDT). Meanwhile, the anticancer drug, doxorubicin hydrochloride (DOX), was further incorporated into the porous structures of Al-MOFs and demonstrated the pH-responsive drug release behavior. Our results show that the near-infrared (NIR) light-induced PDT with chemotherapy (CMT) exhibits excellent antitumor effects. It is believed that the present work highlights the potential of the combination of UCNPs and MOFs and holds great promise for biomedical applications.

ZIF-8@GMP-Tb nanocomplex for ratiometric fluorescent detection of alkaline phosphatase activity

Luminescent metal–organic frameworks (LMOFs) and their functional materials with unique characteristics can provide the basis for the construction of new analytical techniques, which can meet the continuous demand for various fields. In this work, guanosine monophosphate (GMP), terbium ion (Tb3+) and zeolitic imidazolate framework-8 (ZIF-8) are self-assembled to form a ZIF-8@GMP-Tb nanocomplex, which can be utilized as a ratiometric fluorescent probe to monitor alkaline phosphatase (ALP) activity. Specifically, with adding ALP, the fluorescence intensity at 547 nm (one of the characteristic emission peaks of Tb3+) obviously decreased. Meanwhile, the conjugated structure of GMP increased the fluorescence of ZIF-8 (located at 330 nm). The possible mechanism was proposed through the characterization of the materials. Based on the variation of the emission peaks at 330 and 547 nm, the ratiometric fluorescent sensor of ALP has a linear range of 0.25–20 U/L. Moreover, applying this sensing system to the detection of ALP in the human serum sample and ALP inhibitor investigation possesses satisfactory results. This work provides a new perspective for the utilization of ZIF-8 and lanthanide ions in manufacturing simple and sensitive sensors.

Linker Engineering toward Full-Color Emission of UiO-68 Type Metal-Organic Frameworks.

Luminescent metal-organic frameworks (LMOFs) demonstrate strong potential for a broad range of applications due to their tunable compositions and structures. However, the methodical control of the LMOF emission properties remains a great challenge. Herein, we show that linker engineering is a powerful method for systematically tuning the emission behavior of UiO-68 type metal-organic frameworks (MOFs) to achieve full-color emission, using 2,1,3-benzothiadiazole and its derivative-based dicarboxylic acids as luminescent linkers. To address the fluorescence self-quenching issue caused by densely packed linkers in some of the resultant UiO-68 type MOF structures, we apply a mixed-linker strategy by introducing nonfluorescent linkers to diminish the self-quenching effect. Steady-state and time-resolved photoluminescence (PL) experiments reveal that aggregation-caused quenching can indeed be effectively reduced as a result of decreasing the concentration of emissive linkers, thereby leading to significantly enhanced quantum yield and increased lifetime.

Highly efficient and bifunctional Cd(II)-Organic Framework platform towards Pb(II), Cr(VI) detection and Cr(VI) photoreduction

Lead and chromate/dichromate are widely used in manufacturing industry, but Pb(II) and Cr(VI) ions pose fatal threats to human health and the water ecological environment. It is thus highly desirable to develop novel and valid strategies for rapid detection and effective decontamination of these heavy metal ions. Design and assembly of luminescent Metal-Organic Framework (LMOFs) for effective recognition and removal of Pb(II) and/or Cr(VI) from water provide a feasible avenue to address this issue. Herein, a novel Cd(II)-MOF, [(Cd3L2)]·(solvent)x (labeled as compound 1) with bright blue fluorescence was assembled under the solvothermal reaction of triangular ligand 5'-(5-carboxy-1H-benzo [d]imidazole-2-yl)-[1,1':3′,1″-terphenyl]-4,4″-dicarboxylic acid (H3L) and Cd(NO3)2. Given that the unique structure features of 3D stacking framework, i. e. strong π···π conjugative effects of organic linkers, plentiful free imidazole N atoms and carboxyl O atoms, Cd-MOF of 1 was deliberately deployed as bifunctional platform to sense Pb(II)/Cr(VI) and photochemically reduce Cr(VI) to Cr(III). Notably, 1 emits durable bright blue fluorescence and performs rapid quenching sense for Pb2+, Cr2O72− and CrO42−, with ultra low detection limits of 1.89, 4.83 and 2.84 ​ppb, respectively. Moreover, highly toxic Cr(VI) could be rapidly and thoroughly reduced to Cr(III) ions by 1 under the irradiation of mercury lamp, with reliable recycling ability. The possible photoluminescence, quenching and photocatalytic reduction mechanisms also were tentatively proposed.

Tuning Chromophore-Based LMOF Dimensionality to Enhance Detection Sensitivity for Fe3+ Ions.

Herein, we report the synthesis of two new manganese-based luminescent metal–organic frameworks (LMOFs) [Mn0.5(tipe)(1,4-ndc)]n (1) and [Mn(tipe)(1,4-ndc) (H2O)·(DMF)2·(H2O)3]n (2) [tipe = 1,1,2,2-tetrakis(4-(1H-imidazol-1-yl)phenyl)ethene (tipe) and 1,4-ndc = 1,4-naphthalenedicarboxylic acid] constructed from an aggregation-induced emission (AIE) chromophore ligand. Compound 1 can undergo a facile single-crystal-to-single-crystal transformation to form compound 2, which results in an increase in dimensionality from a two-dimensional (2D) network to a three-dimensional (3D) network. Both compounds demonstrate excellent performance for the solution-phase detection of Fe3+ ions through a significant and rapid quench in luminescence emission. Fluorescence titration experiments reveal that compound 2 is more selective toward Fe3+ compared to compound 1 because of its 3D stacking mode. The Ksv value for compound 2 (32 378 M–1) is twice as large as that for compound 1 (15 854 M–1) for the detection of Fe3+ ions. We attribute this significant increase in performance to the increase in dimensionality. In addition, compound 2 demonstrates high selectivity and sensitivity for the detection of Cr3+ cations and Cr2O72– anions.

A new strategy to fabricate multifunctional luminescent MOFs, extending their application range from pH sensing to amino acid information coding

Herein, we propose a new strategy for designing new types of wide range pH-sensitive metal-organic frameworks (MOFs) with double luminescent centers on UiO-66-2OH. The UiO-66-2OH has a ligands-based emission at 530 nm. To introduce another luminescent center, PMA (1,2,4,5-benzenetetracarboxylic acid), as the functional site, is used to substitute the initial ligand, BDC-2OH (2,5-dihydroxyterephthalic acid), of UiO-66-2OH. Eu3+ ions, another luminescent center at 613 nm, are coordinated to the free carboxyl group on PMA. Finally, TTA (2-Thenoyltrifluoroacetone) is coordinated with Eu3+ ions to balance the emission at 613 nm (Eu3+ ions) and 530 nm (BDC-2OH). For the sake of both strong emissions, we explored the loading levels of PMA. The optimized structure is Eu(TTA)@MUM5 (“MUM” is the abbreviation of “Mixed ligand UiO-66-2OH MOFs” and “5” represents the molar percentage of PMA is 50%), which exhibits strong emission at 530 nm (alkaline solution) and 613 nm (neutral solution). Remarkably, the synthesized material has an exponential relationship (R2 = 0.9973) over the pH range of 1.87 to 9.65 and a linear relationship (R2 = 0.9987) when pH = 11.01–13.35. Further experiments have proved that Eu(TTA)@MUM5 could distinguish different amino acids. Based on that, we build an information transferring circle with two coding modes on Eu(TTA)@MUM5 using aseptic acid and arginine as coding factors.

Directional Exciton Migration in Benzoimidazole-Based Metal-Organic Frameworks.

Highly luminescent metal-organic frameworks (MOFs) have recently received great attention due to their potential applications as sensors and light-emitting devices. In these MOFs, the highly ordered fluorescent organic linkers positioning prevents excited-state self-quenching and rotational motion, enhancing their light-harvesting properties. Here, the exciton migration between the organic linkers with the same chemical structure but different protonation degrees in Zr-based MOFs was explored and deciphered using ultrafast laser spectroscopy and density functional theory calculations. First, we clearly demonstrate how hydrogen-bonding interactions between free linkers and solvents affect the twisting changes, internal conversion processes, and luminescent behavior of a benzoimidazole-based linker. Second, we provide clear evidence of an ultrafast energy transfer between well-aligned adjacent linkers with different protonation states inside the MOF. These findings provide a new fundamental photophysical insight into the exciton migration dynamics between linkers with different protonation states coexisting at different locations in MOFs and serve as a benchmark for improving light-harvesting MOF architectures.

Recent Progress in Luminous Particle‐Encapsulated Host–Guest Metal‐Organic Frameworks for Optical Applications

AbstractMetal‐organic frameworks (MOFs) as a unique class of porous crystalline materials have received comprehensive attention in the past decades. Among them, luminescent MOFs (LMOFs) have been a well‐known branch on account of their relevance as optical materials in contemporary era. The establishment of host–guest hybrid LMOF materials has triggered a hot search area owing to the extensive range of applications that can be adjusted by soliciting different functional luminescent guests. Current developments in the thought‐provoking application of host–guest LMOFs have stretched into far‐ranging fields, including light regulation, imaging, sensing, data encryption, etc. This review discusses on the hybridization of MOFs with functional luminescent particles (LPs) as guests for the construction of a series of extraordinary host–guest luminescent composite materials (LP@MOFs). The basic aspects, involving the preconcentration of MOF hosts and luminous guests as well as the comprehensive synthetic strategies of LP@MOFs are introduced. Furthermore, the applications of luminescent LP@MOF materials are highlighted, with a particular emphasis on the present and continuing challenges and the demand trends of such materials that need to be explored.

Highly stable terbium(III)-based metal-organic framework for the detection of m-dinitroaromatics and Fe3+ in water

A highly luminescent three-dimensional terbium-based metal organic framework [Tb(cpia)(H2O)2]n·nH2O (1) has been employed for the selective detection of m-dinitroaromatics and Fe3+. Stability tests suggest that compound 1 exhibits good stability in hot water and acidic and basic conditionswithin the pH range of 4–13. The strong green emission of 1 could be efficiently quenched by 1,3-dinitrobenzene, 2,4-dinitrotoluene, 2,6-dinitrotoluene in ethanol. Significantly, compound 1 can also be used to detect 1,3-dinitrobenzene in aqueous phase with high sensitivity and low detection limit (1.89 μM), indicating the detection of m-dinitroaromatics in aqueous medium can be realized. Furthermore, compound 1 also exhibits superior luminescence quenching behavior towards Fe3+ with high sensitivity and selectivity among various metal cations. In addition, the luminescence quenching mechanisms towards different analytes are also discussed in detail. These results demonstrate that compound 1 is a promising luminescent sensor for the simultaneous selective detection of m-dinitroaromatics and Fe3+ in water.

Devising Mixed-Ligand Based Robust Cd(II)-Framework From Bi-Functional Ligand for Fast Responsive Luminescent Detection of Fe3+ and Cr(VI) Oxo-Anions in Water With High Selectivity and Recyclability.

Environmental issue related applications have globally surfaced as hottest areas of research, wherein luminescent metal-organic frameworks (LMOFs) with functionalized pores put unique signature in real-time monitoring of multiple classes of toxic compounds, and overcome many of the challenges of conventional materials. We report a two-fold interpenetrated, mixed-ligand Cd(II)-organic framework (CSMCRI-11) [Cd1.5(L)2(bpy)(NO3)]·DMF·2H2O (CSMCRI = Central Salt and Marine Chemical Research Institute, HL = 4- (1H-imidazol-1-yl)benzoic acid, bpy = 4,4′-bipyridine) that exemplifies bipillar-layer structure with two different Cd(II) nodes, and displays notable robustness in diverse organic solvents and water. Intense luminescence signature of the activated MOF (11a) is harnessed in extremely selective and fast responsive sensing of Fe3+ ions in aqueous phase with notable quenching constant (1.91 × 104 M−1) and impressive 166 ppb limit of detection (LOD). The framework further serves as a highly discriminative and quick responsive scaffold for turn-off detection of two noxious oxo-anions (Cr2O7 2− and CrO4 2−) in water, where individual quenching constants (CrO4 2−: 1.46 × 104 M−1; Cr2O7 2−: 2.18 × 104 M−1) and LOD values (CrO4 2−: 179 ppb; Cr2O7 2−: 114 ppb) rank among best sensory MOFs for aqueous phase detection of Cr(VI) species. It is imperative to stress the outstanding reusability of the MOF towards detection of all these aqueous pollutants, besides their vivid monitoring by colorimetric changes under UV-light. Mechanism of selective quenching is comprehensively investigated in light of absorption of the excitation/emission energy of the host framework by individual studied analyte.

Series of Luminescent Lanthanide MOFs with Regular SHG Performance.

Second-harmonic generation (SHG) is a kind of nonlinear optical phenomenon which has been widely used in optical devices, and factors influencing its signal are very complex. Here, taking advantage of excellent structural designability and overcoming the limitations of various coordinations of lanthanide metals, for the first time a series of lanthanide metal-organic frameworks (Ln-MOFs) with one particular ligand were synthesized and structurally characterized to study the interference of the SHG signal. The optical performance including single-photon fluorescence and SHG was collected and analyzed. It is found that all 13 kinds of Ln-MOFs can be divided into 2 crystal configurations by their individual space groups and Ln-MOFs with coordinated metal atoms from La to Tb possessing the noncentrosymmetric C2 space group exhibit the SHG property, the intensity of which depends on the type of metal atoms, the pumping wavelength, and the size of the single-crystal particles. This is the first time that the relationship between the nonlinear optical properties and the structure, metal atoms, pumping wavelength, crystal size of the whole series of Ln-MOFs is studied systematically, providing a lot of interesting results and enriching the research scope of nonlinear optics and materials science.

A Novel Luminescent Metal‐Organic Framework as a Remarkable Sensor for Detecting Aristolochic Acids in Biological Fluids

AbstractAbstract: Aristolochic acids (AAs) have caused widespread concern as highly nephrotoxic and carcinogenic substances. Therefore, it is essential to explore a simple and feasible method to detect AAs for disease prevention and clinical diagnosis. In this work, we designed and synthesized a novel luminescent metal organic framework (Zn‐MOF), which has excellent structural stability and fluorescence stability. Notably, the luminescent Zn‐MOF exhibits strong blue emission owing to ligand‐centered electronic transitions, while being capable as a selective sensor for the quantitative detection of AAs in biological fluids with low detection limit. The fluorescence analysis method, possessing the advantages of reliability and high accuracy, further demonstrated that Zn‐MOF has potential applications in monitoring the carcinogen biomarker AAs. Moreover, a paper‐based sensor has been devised by depositing Zn‐MOF on filter paper, which provides a novel strategy for visual, rapid, and on‐site AAs detection with the naked eye.

Silver(I)–Organic Frameworks Showing Remarkable Thermo-, Solvato- And Vapochromic Phosphorescence As Well As Reversible Solvent-Driven 3D-to-0D Transformations

A series of isoreticular Ag(I) luminescent metal-organic frameworks (LMOFs), {[Ag2L2(CH3CN)2](X)2}n (X = ClO4, OTf, and BF4), has been designed, exploiting diphenyl(2-pyrazyl)phosphine (L) as a multidentate linker. At ambient temperature, these compounds emit a bright long-lived phosphorescence (λem = 545-555 nm) with a quantum efficiency as high as 22%, which is the highest value for phosphorescent Ag-LMOFs. The prepared LMOFs also exhibit pronounced thermochromic luminescence, reversibly changing their emission color in the 300-77 K range. These LMOFs also demonstrate prominent solvato- and vapochromic luminescence, which manifest as a reversible change in the emission properties during the removal and recovery of the coordinated and guest MeCN molecules, respectively. Moreover, we have discovered a reversible solvent-driven 3D-to-0D transformation of the framework {[Ag2L2(CH3CN)2](ClO4)2}n into a brightly emissive complex [Ag4L4(ClO4)4]. To the best of our knowledge, the compounds obtained are the first Ag-LMOFs that exhibit thermo-, solvato-, and vapochromic luminescence.

Synthesis of two Cd-MOFs based on flexible trinitrogen ligand for CrO42− detection in harsh alkaline solution

A two-dimensional luminescent metal–organic framework (LMOF), {[Cd(tptb)2(H2O)2]·2NO3}n(1), and a 3-fold interpenetrating three-dimensional framework with a new topology of 3,5-c net, {[Cd(tptb) (H2DOBDC)(H2O)]·DMF}n (2, H2DOBDC2− = 2,5-dihydroxyterephthalate; DMF = dimethylformamide), were synthesized and characterized based on flexible trinitrogen ligands, tptb (1,3,5-tris(4-pyridylsulfanylmethyl)-2,4,6-trimethylbenzene). Interestingly, compound 2 can not only potentially be used as a multi-functional luminescent sensing material for Cr2O72−, CrO42− and Fe3+ ions via luminescence quenching in DMA, but also can be as a highly selective and sensitive sensor for CrO42− at pH 13.0. And the luminescent quenching mechanisms also were explored. Such a Cd-MOF with good pH stability, water stability, interference immunity and regeneration ability can act as an ultrasensitive fluorescent sensor in the field of detection.

Multiple fluorescent sensing responses of a 2D framework structure towards explosive: Synthesis, characterization and sensing performance

In the following work, we reported an optical sensing platform with dual sensing channels for picric acid (PA), named as RS@EuBTC. This sensing platform consisted of supporting matrix derived from luminescent rare earth MOF and a rhodamine-derived sensing probe. By means of XRD, IR, TGA, absorption, emission and excitation spectra, RS@EuBTC's composite structure was confirmed. Its rhodamine absorption component was enhanced by increasing PA concentration in visible region, showing colorimetric sensing behavior. Its rhodamine emission component was enhanced obviously by PA as well, but its Eu emission component was slightly quenched by PA, showing ratiometric fluorescent sensing response towards PA. Linear sensing response towards PA was found for both sensing channels with LOD as low as 4.8 μM. RS@EuBTC depicted good selectivity towards PA over interferents. Its sensing mechanism was convinced as the combination of rhodamine emission turn on effect triggered by PA's protons and Eu emission turn off effect caused by an electron transfer procedure initiated by PA's electron-pulling effect. The novelty of RS@EuBTC localized at its possibility of naked eye detection and dual sensing channels with good selectivity.

Enhanced photoluminescence quantum yield of terbium nano-MOFs synthesized by microwave assisted solvothermal method

In the present work luminescent metal–organic frameworks consisting of terbium ions as the metallic center and 1,4 benzene-dicarboxylic acid (BDC), benzene-tricarboxylic (BTC) acid and 1,3 thiophane-dicarboxylic acid (TDC), as the organic ligands, are synthesized by the microwave assisted solvothermal method at a relatively short time. The samples are studied before and after a thermal annealing process at 400°C. The structural and chemical analysis indicate the formation of nanocrystals of about 8.8 nm, 5.0 nm and 127 nm for BDC, BTC and TDC samples, respectively. All the samples show carbon and oxygen in excess attributed probably to remnants of the N,N-Dimetilformamide used as solvent during the synthesis or to diffused particles from the atmosphere. The luminescent analysis shows a high quantum yield value for the BDC framework, 99.6%, after the annealing process, attributed to an antenna effect; whereas both the BTC and TDC samples show a higher quantum yield before annealing; 64.1% and 13.3%, respectively. The luminescence decay time is also computed in the samples resulting between 1 and 1.5 ms for both BDC and BTC samples, whereas for the TDC sample the decay time was about 0.2 ms. A noticeable daylight visible PL emission is observed in all samples.