Tunable Photoluminescence Properties Research Articles

Solvothermal Synthesis of High‐Quality All‐Inorganic Cesium Lead Halide Perovskite Nanocrystals: From Nanocube to Ultrathin Nanowire

Recently, all‐inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals have drawn much attention because of their outstanding photophysical properties and potential applications. In this work, a simple and efficient solvothermal approach to prepare CsPbX3 nanocrystals with tunable and bright photoluminescent (PL) properties, controllable composition, and morphology is presented. CsPbX3 nanocubes are successfully prepared with bright emission high PL quantum yield up to 80% covering the full visible range and narrow emission line widths (from 12 to 36 nm). More importantly, ultrathin CsPbX3 (X = Cl/Br, Br, and Br/I) nanowires (with diameter as small as ≈2.6 nm) can be prepared in a very high morphological yield (almost 100%). A strong quantum confinement effect is observed in the ultrathin nanowires, in which both the absorption and emission peaks shift to shorter wavelength range compared to their bulk bandgap. The reaction parameters, such as temperature and precursors, are varied to investigate the growth process. A white light‐emitting device prototype device with wide color gamut covering up to 120% of the National Television System Committee standard has been demonstrated by using CsPbBr3 nanocrystals as the green light source. The method in this study provides a simple and efficient way to prepare high‐quality CsPbX3 nanocrystals.

New paradigms for the synthesis of graphene quantum dots from sustainable bioresources

Emerging Graphene Quantum Dots (GQDs)—a new member of the carbon family—have attracted a tremendous research interest in the scientific community due to their small size and tunable photoluminescence properties.

Highly porous photoluminescent diazaborole-linked polymers: synthesis, characterization, and application to selective gas adsorption

Highly porous and photoluminescent diazaborole-linked polymers are targeted by boron–nitrogen bond formation through simple condensation reactions. The resultant polymers exhibit remarkable gas uptake and tunable photoluminescent properties.

Unexpected formation of scheelite-structured Ca1-xCdxWO4 (0 ≤ x ≤ 1) continuous solid solutions with tunable photoluminescent and electronic properties.

Design of a solid solution with tunable functionality is an attractive strategy toward realizing novel devices with multi-functionalities. In this work, a series of Ca1-xCdxWO4 solid solutions in the entire range 0 ≤ x ≤ 1 with tetragonal scheelite structure have been successfully prepared for the first time. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Fourier transform Raman (FT-Raman) spectroscopies indicated that all the nanocrystals have a tetragonal scheelite structure without wolframite phase. Structural refinement data revealed that the lattice volume decreased with the replacement of Ca2+ by Cd2+ ions. UV-Vis diffuse reflectance spectra indicated that optical band gap reduced with the replacement of Ca2+ by Cd2+ ions. Scanning electron microscopic (SEM) images showed that morphologies of the nanocrystals changed with the chemical compositions. The structure evolution of the solid solutions was further investigated by high-resolution transmission electron microscopy (HRTEM). Moreover, the influence of chemical compositions on the photoluminescent and electric performance has been performed and discussed. The reported synthetic approach and findings reported here are important to understand the structure and structure-property relation of scheelite-structured tungstate and molybdate compounds, which has potential applications in the design of other kinds of novel functional materials.

Luminescence properties of Eu3+/CDs/PVA composite applied in light conversion film

In this work, blue-light-emitting carbon dots (CDs) were composited with red-light-emitting europium ions (Eu3+) solutions under the synergistic reaction of polyvinyl alcohol (PVA) to prepare the light conversion film. The formation mechanism of Eu3+/CDs/PVA film was detailedly discussed. It is the first report that this composite was synthesized through direct recombination of CDs and Eu3+ solutions instead of traditional methods based on Eu3+ coordination compound. Furthermore, tunable photoluminescence property can be successfully achieved by controlling the ratio of CDs to doped Eu3+, this property can meet the variable light component requirements for different species of plants.

Dy3+/Eu3+ co-doped CsGd(MoO4)2 phosphor with tunable photoluminescence properties for near-UV WLEDs applications

A series of color tunable Dy3+/Eu3+ co-doped CsGd(MoO4)2(CGM) phosphors were prepared by the conventional solid state reaction. The crystal structure, morphology, vibrational modes, luminescence properties and energy transfer mechanism were investigated. Upon near ultraviolet (n-UV) excitation, Dy3+/Eu3+ co-doped phosphors exhibit the characteristics blue (4F9/2 → 6H15/2), yellow (4F9/2 → 6H13/2) and red (5D0→7F2) emission corresponding to transitions of Dy3+and Eu3+ions. By changing the doping concentration of Dy3+ and Eu3+, the emission hue could be controlled via the energy transfer mechanism. The energy transfer efficiency and critical distance of Dy3+ and Eu3+ have been calculated. The calculated chromaticity coordinates and color correlated temperature of co-doped phosphors lie at the F4 warm white points of standard illuminants.

Preparation of Flower-Like ZnO Nanoparticles by High-Gravity Assisted Ammonia Decomposition Method and Their Photoluminescence Properties

Zinc oxide (ZnO) nanoparticles with tunable particle size and photoluminescence (PL) properties were successfully prepared by a facile ammonia decomposition method in a rotating packed bed (RPB) reactor. The zinc-ammonia complex, generated from chemical process of zinc mineral, reacted with steam to precipitate the precursor of ZnO. It was found that both the particle size of ZnO and the precipitation rates of Zn strongly depended on the steam flow rate, high-gravity level, calcination temperature. The flower-like ZnO with primary particle size of ~45 nm had improved PL performance, which further confirmed the intensification of RPB reactor. Moreover, the results showed that the precipitation rate of Zn could reach up to 98% under the optimized conditions. It was believed that RPB reactors with well mass transfer and mixing performances, short preparation time and low energy consumption would be a promising device for the continuous preparation of nano-ZnO materials.

Enhancement and tuning of photoluminescence properties in Pr3+/Au co-doped antimony oxide glass nanocomposites by thermal treatment

Pr3+/Au3+ co-doped antimony oxide glass nanocomposites has been synthesized in a dielectric glass matrix having composition 15K2O–15B2O3–60Sb2O3–10ZnO (KBSZ) by single-step melt-quenching technique. Au nanoparticles (NPs) are generated in-situ by thermochemical reduction by Sb3+. The Tg has been found to be 290–295 °C as obtained by dilatometry and differential scanning calorimetry. X-ray diffraction (XRD) patterns show the presence of nanocrystalline phase of Au in the as-prepared samples. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) patterns also confirm the presence of Au NPs. UV–Vis absorption spectra shows both the characteristic absorption bands of Pr3+, around 445 nm and Au surface plasmon resonance (SPR), around 620 nm. When excited with 447 nm diode laser, all the nanocomposites show strong orange emissions. The sample containing 0.008 wt% Au gives the maximum emission. This sample is heat treated at 300 °C for different durations. XRD of heat treated samples reveals that crystallization of the glassy matrix initiates at around 480 min heat treatment. The UV–Vis absorption spectra of the heat treated samples show increased absorbance of the SPR band of Au around 620 nm. The SPR band of Au gets more and more widespread with increasing heat treatment duration which is due to rapid rate of Au NP generation by thermochemical reduction at elevated temperature. Variation of PL intensity with heat treatment duration exhibits two maxima (at 45 and 480 min durations). The first one is due to the attainment of the critical size of Au NPs, for which the emission becomes maximum. And the second one is the effect of matrix crystallization, which lowers down the phonon energy of the system and enhances PL intensity by reducing the non-radiative loss. This enhancement and tuning of photoluminescence is enormously useful for various photonic applications.

Tunable photoluminescence properties of Pr3+/Er3+-doped 0.93Bi0.5Na0.5TiO3–0.07BaTiO3 low-temperature sintered multifunctional ceramics

Pr3+/Er3+-doped 0.93Bi0.5Na0.5TiO3–0.07BaTiO3 ceramics have been fabricated at a low sintering temperature of 960°C using a sintering aid of Li2CO3. The effects of energy transfer between Pr3+and Er3+on their photoluminescence properties have been investigated. Our results reveal that the down-conversion emissions of Pr3+are weakened and the lifetimes are shortened by the co-doping of Er3+. As a result, when both Pr3+and Er3+are excited simultaneously, with increasing the concentration of Er3+, the green emissions from Er3+increase but the red emissions from Pr3+decrease. Moreover, the emission color of the ceramics can be reversibly changed between red, yellow and yellowish green by using excitation sources of different wavelengths. Strong up-conversion green emissions with short lifetimes arisen from Er3+have also been observed for the ceramics under the excitation of 980nm. Owing to the Li2CO3 sintering aid, the low-temperature sintered ceramics also exhibit reasonably good ferroelectric and piezoelectric properties, and hence should be promising for multifunctional applications such as electro-optical coupling devices.

Surface-plasmon mediated photoluminescence enhancement of Pt-coated ZnO nanowires by inserting an atomic-layer-deposited Al2O3 spacer layer

Surface-plasmon mediated photoluminescence emission enhancement has been investigated for ZnO nanowire (NW)/Pt nanoparticle (NP) nanostructures by inserting an Al2O3 spacer layer. The thickness of the Al2O3 spacer layer and of the Pt NPs capped on the ZnO NWs are well controlled by atomic layer deposition. It is found that the photoluminescence property of the ZnO NW/Al2O3/Pt hybrid structure is highly tunable with respect to the thickness of the inserted Al2O3 spacer layer. The highest enhancement (∼14 times) of the near band emission of ZnO NWs is obtained with an optimized Al2O3 spacer layer thickness of 10 nm leading to a ultraviolet–visible emission ratio of 271.2 compared to 18.8 for bare ZnO NWs. The enhancement of emission is influenced by a Förster-type non-radiative energy transfer process of the exciton energy from ZnO NWs to Pt NPs as well as the coupling effect between excitons of ZnO NWs and surface plasmons of Pt NPs. The highly versatile and tunable photoluminescence properties of Pt-coated ZnO NWs achieved by introducing an Al2O3 spacer layer demonstrate their potential application in highly efficient optoelectronic devices.

Electrochemical Methods to Study Photoluminescent Carbon Nanodots: Preparation, Photoluminescence Mechanism and Sensing.

With unique and tunable photoluminescence (PL) properties, carbon nanodots (CNDs) as a new class of optical tags have been extensively studied. Because of their merits of controllability and sensitivity to the surface of nanomaterials, electrochemical methods have already been adopted to study the intrinsic electronic structures of CNDs. In this review, we mainly deal with the electrochemical researches of CNDs, including preparation, PL mechanism, and biosensing.

Stimuli-Responsive Polyoxometalate/Ionic Liquid Supramolecular Spheres: Fabrication, Characterization, and Biological Applications

We report fabrication, characterization, and potential applications of polyoxometalate (POM)/ionic liquid (IL) supramolecular spheres in water for the first time. These supramolecular spheres have highly ordered structures and show excellent reversible self-assembly and tunable photoluminescence properties, which can be manipulated by adjusting pH of the aqueous solution. Specifically, the formation of POM/IL supramolecular spheres results in quenching of fluorescence emitted by Eu-POM because hopping of the d1 electron in the POM molecule is blocked by hydrogen bond existing between the oxygen atom of POM and the carboxylic acid group of IL. However, the fluorescence can be completely recovered by gradually increasing pH of the aqueous solution due to the pH-induced deprotonation of the carboxylic acid group of IL, which results in disassembly of the fabricated supramolecular spheres. Applications of these stimuli-responsive photoluminescent POM-based supramolecular materials are demonstrated in biological media. Dual signaling responses of turbidity and fluorescence are observed simultaneously in the detection of urease and heavy metals based on pH-induced disassembly of the supramolecular spheres during the biochemical events in aqueous solution. In addition, guest molecules are encapsulated into the supramolecular spheres, and controlled release of these entrapped molecules is demonstrated in the presence of external stimuli. This study shows potential of stimuli-responsive POM/IL supramolecular materials in biological applications.

Correction: A series of nano/micro-sized metal–organic frameworks with tunable photoluminescence properties

Correction for ‘A series of nano/micro-sized metal–organic frameworks with tunable photoluminescence properties’ by Yuhua Zheng et al., CrystEngComm, 2015, 17, 2321–2326.

Colour-tunable quantum dots/poly(NIPAM-co-AAc) hybrid microgels based on electrostatic interactions

Colour-tunable QD/poly(NIPAM-co-AAc) hybrid microgels have been synthesized by encapsulating and entrapping positively charged QDs with pH-responsive negatively charged microgels with tunable photoluminescent properties.

A facile method for the synthesis of CuInS2–ZnS quantum dots with tunable photoluminescent properties

CuInS2/CuInS2–ZnS quantum dots showed excellent tunable photoluminescent properties, which demonstrate great potential for practical applications due to their non-toxicity and excellent optical properties.

Ethylene diamine mediated cobalt nanoparticle studded graphene oxide quantum dots with tunable photoluminescence properties

The present study demonstrates ethylene diamine mediated in situ synthesis of cobalt oxide nanoparticles (Co3O4NPs) studded on graphene oxide quantum dots (GOQDs) showing reversible on/off fluorescence switching.

Room-temperature synthesis of three-dimensional porous ZnO@CuNi hybrid magnetic layers with photoluminescent and photocatalytic properties

A facile synthetic approach to prepare porous ZnO@CuNi hybrid films is presented. Initially, magnetic CuNi porous layers (consisting of phase separated CuNi alloys) are successfully grown by electrodeposition at different current densities using H2 bubbles as a dynamic template to generate the porosity. The porous CuNi alloys serve as parent scaffolds to be subsequently filled with a solution containing ZnO nanoparticles previously synthesized by sol-gel. The dispersed nanoparticles are deposited dropwise onto the CuNi frameworks and the solvent is left to evaporate while the nanoparticles impregnate the interior of the pores, rendering ZnO-coated CuNi 3D porous structures. No thermal annealing is required to obtain the porous films. The synthesized hybrid porous layers exhibit an interesting combination of tunable ferromagnetic and photoluminescent properties. In addition, the aqueous photocatalytic activity of the composite is studied under UV−visible light irradiation for the degradation of Rhodamine B. The proposed method represents a fast and inexpensive approach towards the implementation of devices based on metal-semiconductor porous systems, avoiding the use of post-synthesis heat treatment steps which could cause deleterious oxidation of the metallic counterpart, as well as collapse of the porous structure and loss of the ferromagnetic properties.

Hydrothermal fabrication of multi-functional Eu3+ and Tb3+ co-doped BiPO4: Photocatalytic activity and tunable luminescence properties

We demonstrated for first time the tunable photoluminescence (PL) properties and photocatalytic activity of the Tb3+ and Eu3+ co-doped BiPO4 assemblies. They are fabricated via a facile hydrothermal approach. Through co-doping of Eu3+ and Tb3+ ions and changing the doping ratio, the emission color of the co-doped BiPO4 phosphors can be tuned precisely from green to yellow and red. Meanwhile, a very efficient energy transfer from Tb3+ to Eu3+ can be observed. Fascinatingly, a warmwhite color has been realized in the co-doped sample by tuning the ratio of Tb3+/Eu3+ to a certain value as displayed in the CIE chromaticity diagram. The doped BiPO4 samples also exhibit significantly enhanced photocatalytic activity compared to the pristine BiPO4 pertaining to Rhodamine (RhB) degradation under UV light. This enhancement should be attributed to the trapping electron effect induced by ion doping that endows BiPO4 with high separation of photoinduced electron–hole pairs, thereby greatly promoting the photocatalytic reactivity. It was corroborated by the electrochemical impedance spectra (EIS). Moreover, the crystal structure, microstructure and optical properties of as-prepared samples were investigated in details.

Tunable photoluminescence properties and energy transfer in oxyapatite-based Ca2Tb8(SiO4)6:Eu3+ phosphors for UV-LEDs

New phosphors Ca2Tb8–xEux(SiO4)6O2 with color-tunability were synthesized in this work. The Rietveld refinement indicated that the prepared phosphors were crystallized to a hexagonal structure with space group P63/m (no. 176). When Eu3+ ions were introduced into Ca2Tb8(SiO4)6O2, characteristic red–orange emissions of Eu3+ ions and the green emission of Tb3+ ions were obtained. Eu3+-doped phosphors emitted with enhanced intensity and had broader excitation spectra than the undoped Ca2Tb8(SiO4)6O2 phosphors. As Eu3+ content increased, a decline in Tb3+ emission was observed owing to resonant energy transfer from the 5D3 level of Tb3+ ions to the 5D0 level of Eu3+ ions. Moreover, the transfer of energy from Tb3+ ions to Eu3+ ions proceeded via a dipole–dipole interaction, and the critical distance for this energy transfer was calculated to be 7.2Å. The efficiency of energy transfer in Ca2Tb8−xEux(SiO4)6O2 increased from 72% to 87% with an increase in the Eu3+ concentration, x, from 0.02 to 0.08. The emitted color of Ca2Tb8−xEux(SiO4)6O2 was tuned from green to red via controlling the concentration of Eu3+ ions. Meanwhile, the optimum phosphor system Ca2Tb7.94Eu0.6(SiO4)6O2 exhibited adequate thermal stability even at 200°C and the corresponding activation energy was calculated to be 0.027eV. These results suggest that Ca2Tb8(SiO4)6O2:Eu3+ may be potential phosphors for the application in UV LEDs.

Synthesis and Optical Properties of CdTe<SUB><I>x</I></SUB>Se<SUB>1-<I>x</I></SUB>-Based Red to Near-Infrared Emitting Quantum Dots

A series of red to near-infrared (NIR) emitting quantum dots (QDs) with spherical morphologies and tunable photoluminescence (PL) properties have been synthesized by a facile organic route using octadecene (ODE) as solvent and oleic acid (OA) as single capping agent. CdSe cores with the average size of 4.5 nm display the typical optical behaviors with the PL emission peak around 610 nm. The coating CdZnS shells are introduced on the surface of CdSe cores for improving the photostability and PL efficiency of the initial QDs. As the thickness of CdZnS shells increasing, the gradual red-shift of emission wavelength varying from 617 to 634 nm of the resulting QDs can be observed, along with the remarkable increase of PL quantum yield (QY). The composition-dependent CdTe(x)Se(1-x) (CdTeSe) cores with the emission in NIR region are easily carried out by adjusting the molar ratio of Se/Te. The abnormal variation of optical bowling effect is mainly ascribed to the composition effect of alloyed QDs. Compared with CdTe0.1Se0.9/CdZnS core/shell QDs, the introducing of CdZnS shells on CdTe0.05Se0.95 cores can exhibit better passivation effect on surface status, consequently leading to the red-shifted emission peaks in the range of 739-752 nm with the maximum PL QY reaching up to 45.09%. The unique PL properties of CdTeSe-based QDs in the red to NIR range make these core/shell QDs attractive for future biological sensing and labeling applications.