Thermochromic luminescent properties of a tetrazole-functionalized iodocuprate without cuprophilic interaction

The 1-tetrazole-4-imidazole-benzene (HL) used as a tetrazole-functionalized spacer constructs 3-D [Cu2(μ3-I)(L)]n (1) with longer Cu⋯Cu distances to eliminate the existence of cuprophilic interaction. 1 shows important thermochromic luminescence and its emission maximum exhibits a gradual red shift with increasing temperature, indicating that 1 is a potential application for a luminescent thermometer with a wide range. Of particular interest, the thermochromic luminescent properties of the reported CuI-tetrazolate systems have not been investigated, while this work first reveals that CuI-tetrazolate system without cuprophilic interaction generates remarkable thermochromic luminescence. Moreover, 1 exhibits selectively photocatalytic degradation of methylene blue (MB) under UV light irradiation, and its density functional theory calculation has also been performed.publishe

Syntheses and luminescent properties of a series of new lanthanide azelates

A series of new lanthanide azelates [Ln(aze)(Haze)(H2O)]·H2O {Ln = La (1a), Ce (1b), Pr (1c); H2aze = azelaic acid}, [Ln2(aze)3(phen)2]·H2O [Ln = Nd (2a), Er (2b); phen = 1,10-phenanthroline], [Sm(aze)(Haze)(phen)]·2H2O (3), [Gd(aze)(phen)2]·ClO4 (4) and (Hphen)[Tb2(aze)2(phen)4]·3ClO4 (5) were hydrothermally prepared and structurally characterized.1a-c are isostructural and show 3-D framework based on 1-D infinite [Ln-O-Ln]n chain. 2a-b exhibit sql layer, while 3 displays 1-D chain, where phen ligands locate at both sides of the chain. The Ln3+ ions of 4 and 5 are connected by aze2− into two different types of rare cationic 1-D chains. The luminescent investigations show that both 2a and 2b exhibit interesting NIR luminescence and 5 displays a good potentiality as a luminescent sensor targeted for Fe3+ ion. Of particular interest, lanthanide azelates have not been to date documented, while this work presents the only examples of lanthanide azelates exhibiting luminescent properties. The magnetic properties of some lanthanide azelates were also investigated.publishe

An unprecedented binodal (4,6)-connected Co(II) MOF as dual-responsive luminescent sensor for detection of acetylacetone and Hg2+ ions

A new Co(II) organic framework, {[Co2(L)(hfpd)(H2O)]·1.75H2O}n (1) (H4hfpd = 4,4′-(hexafluoroisopropylidene)diphthalic acid, L = 4,4′-bis(imidazol-1-yl)-biphenyl) was hydrothermally synthesized and characterized. 1 possesses an unusual (4,6)-connected layered network architecture. Fluorescence titration results present that 1 is rarely dual-responsive probe to detect acetylacetone and Hg2+ ions by luminescence quenching.publishe

Hydrothermal combustion synthesis and characterization of Sr2CeO4 phosphor powders

In this paper, the blue-light-emitting Sr2CeO4 phosphor powders were prepared by hydrothermal combustion reactions and a subsequent sintering process. During the process, the mixed urea and glycine were both used as leavening agent and fuel. The particle crystallization, surface morphology as well as the luminescence intensities of the Sr2CeO4 phosphor powders were effectively improved by adjusting the amount of glycine and post-sintering temperatures. The Sr2CeO4 phosphor exhibited strong crystallization and well-distributed spherical particle after optimization. Moreover, the intense blue-light emission band with the maximum at 468 nm in the range of 400–600 nm was observed as excited with ultraviolet light 277 nm. In particular, after the precursors were heat-treated at 1100 °C, the samples could be well-excited around 350 nm. The excitation bands were ascribed to the charge transfer from O to Ce, and the enlarged excitation range may facilitate its uses in optoelectronic fields.publishe

Combustion synthesis of Ce2LuO5.5:Eu phosphor nanopowders: structure, surface and luminescence investigations

The spherical shape, uniform size and small degree of agglomeration of the particles play crucial roles in promoting the practical applications of the phosphor powders. In this paper, the novel Eu3+ -doped cerium lutetium Ce2LuO5.5 composite nanopowders with a cubic fluorite structure were prepared via a typical solution combustion route, and their internal structure, surface morphology as well as luminescence properties were investigated. The Eu3+ could substitute in either Lu3+ or Ce4+ sites and the existence of oxygen vacancy was confirmed in the composite by X-ray diffraction and Raman spectra techniques. Without the addition of surfactant, most of the as-prepared particles were bound together, and the luminescence was very weak even after a sintering process. Assisted with appropriate polyvinyl alcohol (PVA) surfactant in the combustion reaction and a subsequent heat-treatment process, the bound-particles were evidently separated and seemed to be nearly spherical shape. The particle size could be controlled to 30–120 nm and the luminescence was enhanced by adjusting the subsequent sintering temperature. Excited with 466 nm blue light, the nanopowders exhibited characteristic 5D0 → 7FJ (J  =  0–4) emission transition of Eu3+ and showed enhanced red luminescence as Eu3+ occupied Ce4+ site rather than Lu3+ site. The maximum emission was obtained as 40 mol% Eu substitutes Ce in the composite. Due to the coincidence of 466 nm excitation light with the emission of InGaN chips in white light-emitting diodes, the surface-morphology improved Eu-doped Ce2LuO5.5 phosphor nanopowders have a potential application in solid state lighting fields.publishe

Ln3+ (Ln = Eu, Dy) - doped Sr2CeO4 fine phosphor particles: wet chemical preparation, energy transfer and tunable luminescence

The Sr2CeO4:Ln3+ (Ln = Eu, Dy) fine phosphor particles were prepared by a facile wet chemical approach, in which the consecutive hydrothermal-combustion reaction was performed. The doping of Ln3+ into Sr2CeO4 has little influence on the structure of host, and the as-prepared samples display well-crystallized spherical or elliptical shape with an average particle size at about 100–200 nm. For Eu3+ ions-doped Sr2CeO4, with the increase of Eu3+-doping concentration, the blue light emission band with the maximum at 468 nm originating from a Ce4+ → O2− charge transfer of the host decreases obviously and the characteristic red light emission of Eu3+ (5D0→7F2 transition at 618 nm) is enhanced gradually. Simultaneously, the fluorescent lifetime of the broadband emission of Sr2CeO4 decreases with the doping of Eu3+, indicating an efficient energy transfer from the host to the doping Eu3+ ions. The energy transfer efficiency from the host to Eu3+ was investigated in detail, and the emitting color of Sr2CeO4:Eu3+ can be easily tuned from blue to red by varying the doping concentration of Eu3+ ions. Moreover, the luminescence of Dy3+-doped Sr2CeO4 was also studied. Similar energy transfer phenomenon can be observed, and the incorporation of Dy3+ into Sr2CeO4 host leads to the characteristic emission of 4F9/2 → 6H15/2 (488 nm, blue light) and 4F9/2 → 6H13/2 (574 nm, yellow light) of Dy3+. The Sr2CeO4:Ln3+ fine particles with tunable luminescence are quite beneficial for its potential applications in the optoelectronic fields.publishe

Efficient green-emitting Tb3+-doped di-ureasil coating phosphors for near-UV excited light-emitting diodes

Light-emitting diodes (LEDs) are replacing conventional lighting sources, like incandescent and fluorescent lamps, due to their higher efficiency, lower energy consumption and environmental friendliness characteristics. Additional applications envisaging “engineered light” able to control the human circadian rhythm are now in place with emphases on green-emitting LEDs. In this work, transparent and flexible coatings based on organic–inorganic di-ureasil hybrids doped in-situ with a terbium (Tb3+) complex involving salicylic acid as ligands were synthesized. The materials are transparent, essentially amorphous and thermal stable up to 180 °C. Under near-UV excitation, bright green emission with high quantum yield (0.565 ± 0.057) and enhanced photostability are observed. Green-emitting prototypes were fabricated using a commercial near-UV-emitting LED (NUV-LED) combined with the Tb3+-doped di-ureasil coating showing narrow-band green emission with yellowish-green color coordinates (Commission Internationale de l'Éclairage, CIE 1931) of (0.329, 0.606) and high luminous efficacy (21.5 lm/W). This efficacy is the largest one reported for analogous prototypes formed by an NUV-LED coated with a green-emitting phosphor prepared under mild synthetic conditions (<100 °C), demonstrating that in-situ formation of carboxylate lanthanide-based complexes is an energy saving process with potential for solid-state lighting and backlight for flexible displays.publishe

Functional nanostructured chitosan–siloxane hybrids

New organic–inorganic hybrids were prepared by a sol–gel method from the biopolymer chitosan and a silane coupling agent, 3-isocyanatopropyltriethoxysilane (ICPTES), in which covalent bridges, essentially composed of urea, bond the chitosan to the poly(siloxane) network. The structural characterization of the advanced chitosan–siloxane hybrids was performed by Fourier transform infrared spectroscopy, X-ray diffraction and 29Si and 13C nuclear magnetic resonance. The presence of siloxane nanodomains was detected by small angle X-ray diffraction. The chitosan–siloxane hybrids are bifunctional materials with interesting photoluminescent features and bioactive behaviour. The photoluminescence spectra display an additional high-energy band with longer lifetime, relatively to the characteristic emission of pure chitosan. This band is associated with electron–hole recombinations arising from silicon-related defects at the surface of the siliceous nanodomains. The bioactive behaviour of these materials was also evaluated; the apatite formation was shown to depend on the amount and arrangement of silanol groups

Smart optical sensors for internet of things: integration of temperature monitoring and customized security physical unclonable functions

Nowadays, the Internet of Things (IoT) has an astonishingly societal impact in which healthcare services stand out. Amplified by the COVID-19 pandemic scenario, challenges include the development of authenticatable smart IoT devices with the ability to simultaneously track people and sense in realtime human body temperature aiming to infer a health condition in a contactless and remote way through user-friendly equipment such as a smartphone. Univocal smart labels based on quick response (QR) codes were designed and printed on medical substrates (protective masks and adhesive) using flexible organicinorganic luminescent inks. Luminescence thermometry and physical unclonable functions (PUFs) are simultaneously combined allowing non-contact temperature detection, identification, and connection with the IoT environment through a smartphone. This is an intriguing example where luminescent inks based on organic-inorganic hybrids modified by lanthanide ions are used to fabricate a smart label that can sense temperature with remarkable figures of merit, including maximum thermal sensitivity of Sr = 1.46 %K−1 and temperature uncertainty of δT = 0.2 K, and an authentication methodology accuracy, precision, and recall of 96.2%, 98.9%, and 85.7%, respectively. The methodology proposed is feasibly applied for the univocal identification and mobile optical temperature monitoring of individuals, allowing the control of the access to restricted areas and the information transfer to medical entities for post medical evaluation towards a new generation of mobile-assisted eHealth (mHealth).publishe

Functional mobile-based two-factor authentication by photonic physical unclonable functions

Given the rapid expansion of the Internet of Things and because of the concerns around counterfeited goods, secure and resilient cryptographic systems are in high demand. Due to the development of digital ecosystems, mobile applications for transactions require fast and reliable methods to generate secure cryptographic keys, such as Physical Unclonable Functions (PUFs). We demonstrate a compact and reliable photonic PUF device able to be applied in mobile-based authentication. A miniaturized, energy-efficient, and low-cost token was forged of flexible luminescent organic–inorganic hybrid materials doped with lanthanides, displaying unique challenge–response pairs (CRPs) for two-factor authentication. Under laser irradiation in the red spectral region, a speckle pattern is attained and accessed through conventional charge-coupled cameras, and under ultraviolet light-emitting diodes, it displays a luminescent pattern accessed through hyperspectral imaging and converted to a random intensity-based pattern, ensuring the two-factor authentication. This methodology features the use of a discrete cosine transform to enable a low-cost and semi-compact encryption system suited for speckle and luminescence-based CRPs. The PUF evaluation and the authentication protocol required the analysis of multiple CRPs from different tokens, establishing an optimal cryptographic key size (128 bits) and an optimal decision threshold level that minimizes the error probability.publishe