Intense Blue Emission Research Articles

A single-phased Ca4(PO4)2O: Tm3+, Tb3+, Eu2+ white light-emitting phosphor with tunable emission color

The single-phased white light-emitting Ca4(PO4)2O: Tm3+, Tb3+, Eu2+ phosphors with tunable color emission were synthesized by solid-state reaction method. The photoluminescence properties, crystal structure, decay time and cross-relaxation from Tm3+ to Eu2+ were investigated in detail. Under excitation of 352 nm, Tm3+ singly doped Ca4(PO4)2O (denoted as TTCP) phosphors exhibited an intense emission peak at 458 nm attributed to 1D2 → 3F4 transition of Tm3+ ions and a broad emission peak in the range of 400–411 nm ascribed to oxygen vacancies in TTCP host. The emission intensity of oxygen vacancies decreases along with the increasing of Tm3+ doping concentration due to the substitution of Ca2+ and oxygen vacancies sites by Tm3+ ions. For Tm3+ and Eu2+ co-doped TTCP phosphors, the blue emission intensity (458 nm) of Tm3+ ions obviously decreased and the red emission intensity (624 nm) with of Eu2+ ions increased due to Eu2+ doping. The cross-relaxation from Tm3+ to Eu2+ ions was further demonstrated by the decay times of TTCP: 0.03 Tm3+, yEu2+ phosphors monitoring the emission peak at 458 nm. Further, Tb3+ ions were also introduced in the TTCP phosphor for a green emission and Tb3+ singly-doped TTCP phosphor displays the emission peaks at 488 nm and 545 nm due to the typical5D4→7F5 and 5D4→7F5 transition of Tb3+ ions, respectively. Finally, TTCP: Tm3+, Tb3+, Eu2+ phosphor was obtained and emitted the white light with the blue (458 nm), green (545 nm), and red (603 nm) emission bands under excitation of 352 nm. Especially, white light with tunable color temperature (3000 K–6000 K) and high color rendering index (Ra > 90) can be easily acquired. A neutral white light with high color rendering index (Ra 91.1) can be achieved for the TTCP: 0.03 Tm3+, 0.25 Tb3+, 0.004Eu2+ phosphor.

Controllable phase/morphology tailoring of REF3 and NaREF4 (RE = La-Lu, Y), and insights into the up-conversion luminescence of GdF3:Yb3+/Tm3+ spheres

Four typical rare earth fluorides of hexagonal/orthorhombic REF3 and hexagonal/cubic NaREF4 (RE = La-Lu, Y, excluding radioactive Pm), have been hydrothermally synthesized from mixed solutions of the rare earth nitrate solutions and ammonium fluoride (NH4F), in the presence of EDTA-2Na. The phase and the morphology are closely related to the ionic radius of RE3+. Large RE3+ ions, La3+, Ce3+, Pr3+, Nd3+ and Sm3+, crystallize in hexagonal REF3 (nanocrystals), and middle RE3+ ions (RE = Eu-Dy) crystallize in orthorhombic REF3 (micron-sized spheres/polyhedral micro-crystallites). For small RE3+ ions, Ho3+, Er3+, Tm3+, Yb3+ and Y3+, they tend to being incorporated into the host lattice of cubic NaREF4 (submicron spheres). However, the smallest Lu3+ tends to crystallizing in orthorhombic LuF3. Varying the F-/RE3+ molar ratio (R) and the reaction temperature can efficiently induce the phase/morphology evolution of rare earth fluorides. Increasing R up to 10–30 yielded hexagonal NaREF4 (RE = Dy, Tb, Gd, Eu, Sm, micron prisms), although the original products were orthorhombic REF3 (RE = Dy, Tb, Gd, Eu) and hexagonal SmF3 at R = 5. However, increasing R is inefficient to the phase transition for large RE elements of La, Ce, Pr, Nd. Lowering the reaction temperature from 180 °C to 80 °C gave rise to the phase transition from orthorhombic LuF3 to cubic NaLuF4. GdF3:Yb3+,Tm3+ spheres exhibited intense blue emission at ~476 nm (1G4 → 3H6 transition of Tm3+), deep-red emission at ~646 nm (1G4→3F4 transition of Tm3+), and near-infrared emission at ~695 nm (3F2,3 → 3H6 transitions of Tm3+) under the 980 nm infrared excitation. The intense near-infrared emission under the infrared excitation suggested that they might hold great potential in bio imaging application.

Laser-induced thermal effect and the role of Nd3+ in Tm3+/Yb3+/Nd3+ triply doped LaNbO4 up-conversion phosphors under 808 nm excitation

In this work, intense blue up-conversion (UC) luminescence in LaNbO4: Tm3+/Yb3+/Nd3+ phosphors were obtained under the excitation of 808 nm. The laser-induced thermal effect and the role of Nd3+ in this type of phosphors were discussed. Compared with Tm3+ singly doped and Tm3+/Yb3+ doubly doped samples, thousands-fold and 30-fold overall enhancement in the blue emission intensity of Tm3+ in Tm3+/Yb3+/Nd3+ triply doped LaNbO4 were achieved with the help of Nd3+ sensitizing and the energy transfer bridging Yb3+ ion. The luminescence-enhancement effect exhibited a strong dependence on Nd3+ doping concentration, and the optimal concentration of Nd3+ was found to be 1.0 mol%. Once the doping concentration of Nd3+ exceeded this value, concentration dependent luminescence quenching occurred. Moreover, the laser-induced thermal effect on Tm3+-doped samples was investigated by using Er3+-doped sample as the thermal probe. It was found that the elevation of sample temperature induced by laser irradiation depended on both the doping concentrations of Nd3+ and the excitation power density of 808 nm laser.

Synthesis of blue‐emitting AlN:Eu2+ spherical phosphors by carbothermal reduction nitridation method

AbstractIn this study, blue‐emitting AlN:Eu2+ spherical phosphors were successfully synthesized for the first time by the carbothermal reduction nitridation (CRN) method, assisted with high nitrogen pressure, appropriate synthesis temperature, and the addition of CaF2. The influence of typical experimental parameters, such as N2 pressure, heating temperature, CaF2 content and Eu2+ concentration on the morphologies and luminescence properties of AlN phosphors were comprehensively investigated. The formation mechanism of spherical morphology were significantly proffered, indicating that sufficient liquid Ca‐aluminates during the AlN growth stage were essential for the spheroidization process under the action of surface tension. The synthesized AlN:Eu2+ spherical phosphors presented an intense blue emission band centered in the range of 427‐ 476 nm relative to the reaction temperature. The lifetime of AlN:Eu2+ phosphor was calculated to be around 1.89 μs. The temperature‐dependent PL spectra suggested that the emission band did not shift until 225°C. In addition, the spectral analysis strongly suggested that the luminescence property of AlN:Eu2+ phosphors was significantly enhanced by the large particle size, spherical morphology, reduced impurity content, and appropriate Eu2+ concentration.

Tunable dual emission of Bi3+ and Mn4+ co-doped LaMg0.598Nb0.402O3 double perovskite via energy transfer for plant growth lighting

A series of Bi3+ and Mn4+ co-doped LaMg0.598Nb0.402O3 (LMNO) phosphors via a conventional high-temperature solid-state reaction. Typically, LMNO: Bi3+ shows blue emission with a peak at 450 nm under 315 nm excitation. Upon excitation at 330 nm, Bi3+ and Mn4+ co-doped LMNO phosphors present dual emission, where the blue emission is mainly from the 3P1 → 1S0 transition of Bi3+ and the red emission is attributed to the 2E → 4A2 transition of Mn4+. The red emission of the Mn4+ ions could be enhanced three times via Bi3+→Mn4+ energy transfer compared to the non-codoped samples. The relative intensities of blue emission and red emission can be easily controlled by changing the concentrations of Bi3+ and Mn4+ ions. Therefore, the emission spectra can match well with the absorption of four dominating pigments in plants. These results indicate LMNO: Bi3+, Mn4+ phosphors have potential applications in agricultural fields for promoting plant growth.

Multisite-Occupancy-Driven Intense Narrow-Band Blue Emission from Sr5SiO4Cl6:Eu2+ Phosphor with Excellent Stability and Color Performance.

The development of an efficient blue phosphor with remarkable thermal stability required for high-quality white-light-emitting diodes (WLEDs) remains an exigent task and mainly concerned BaMgAl10O17:Eu2+ (BAM:Eu). Despite the outstanding performance of BAM:Eu, the reduction in luminescence efficiency under long-term operation results in numerous researches on new hosts having lattice rigidity with symmetrical coordination environment. Therefore, we have synthesized a competent blue-emitting Eu2+-activated Sr5SiO4Cl6 (SSC) phosphors. The admirable rigidity of these phosphors with three Sr polyhedra Sr(I)O9, Sr(II)O7, and Sr(III)O8 assessed from Rietveld refinement indicate the dense connectivity in the crystal structure, and the ab initio calculations further support the firm electronic band structure. The broad excitation from 250 to 450 nm suitably matches the absorption band of a near-UV (n-UV) LED chip. The phosphor exhibited bright blue emission with internal quantum yield and color purity > 90% which contribute to the slender fwhm of 33 nm. The first-principle calculation indicates the most stable site for Eu2+ substitution as Sr(III)O8, and the experimental results agreed with this fact as well. The synthesized phosphor displayed an excellent thermal stability which is superior to that of the commercial BAM:Eu phosphor. The excellent thermal stability may be owed to the highly symmetric coordination environment of Eu2+ in the SSC host that are revealed from the distortion and charge density distribution calculation by density functional theory. The blue phosphor was further utilized for WLEDs and displayed white light with a high color-rendering index and suitable correlated color temperature, which is ideal for practical applications in warm WLEDs.

Novel blue emitting Tm3+ activated lanthanum molybdate: Investigations on luminescence behaviour and Judd-Ofelt theoretical analysis

Novel blue emitting thulium doped La2(MoO4)3 nanophosphors were synthesized by facile co-precipitation method and the spectroscopic features were systematically studied on the basis of Judd-Ofelt analysis. The tetragonal phase formation of Tm3+ doped La2(MoO4)3 with space group I41/a is confirmed from the XRD analysis and the growth mechanism by oriented attachment is revealed by TEM analysis. The 1D2→3F4 transition at 453 nm is the dominant emission peak of Tm3+ in the photoluminescence emission spectra and offers major contribution towards the intense blue emission of the phosphor material. The Judd-Ofelt intensity parameters exhibit the trend Ω2>Ω4>Ω6, which point out the asymmetric site occupancy of Tm3+ ions in the host matrix. The estimated higher branching ratio for 1D2→3F4 blue emission of Tm3+ signifies it as a potential laser emission transition. The CIE chromaticity co-ordinates of optimized La1.94Tm0.06(MoO4)3 nanophosphors falls in the blue region of the chromaticity diagram with co-ordinates (0.214,0.097).

Tunable Single‐Molecule White‐Light Emission in Stimuli‐Responsive Hydrogel

AbstractWhite‐light emitting materials based on single‐molecules are of great interest owing to the simple fabrication process and good stability of such materials. However, among limited reports on single‐molecule white light‐emitting materials, the majority of systems are based on organic solvents. Here, a single‐molecule white‐light emitting hydrogel is prepared through the combination of a protonation sensitive fluorophore with a temperature sensitive hydrogel. The mechanism of this system is based on adjusting the ratio of protonated and deprotonated fluorophores through the thermally controllable hydrophobic property of the hydrogel internal microstructure. The fluorophore emits intense blue and yellow emission in its protonated and deprotonated states, respectively; hence, the luminescence of the hydrogel changes color as a function of temperature and [H+], achieving a white color under certain conditions. On the basis of these results, a multicolor light‐emitting device (LED) and a white‐light LED are realized by placing the prepared hydrogel on a conductive substrate over a UV LED chip.

Structural features, low-temperature luminescence properties of Li-doped SnO2 nanobelts and their transitional temperature

Li-doped SnO2 nanobelts have been fabricated by thermal evaporation based on vapor-solid (VS) growth mechanism. The three feature-peaks of Raman scattering spectra at 475 cm −1 (Eg), 634 cm −1 (A1g), and 776 cm −1 (B2g) at room temperature indicate that the samples still keep the rutile structure. One vibration mode at 591 cm−1 is observed from the Li-doped SnO2 nanobelts due to a slight distortion of SnO2. XPS spectra indicate that lithium is incorporated mainly in substitutional sites in the rutile structure of SnO2. The low-temperature (less than 90 K) photoluminescence properties show that there is an intensive broadband blue light emission centered at 480 nm (BL, 2.583 eV). When the temperature is larger than 90 K, the blue light emission peak is quenched and one yellow light emission centered at 580 nm (YL, 2.138 eV) is dominated. The analyses of Gaussian-fitted from 10 to 90 K reveal that the three peaks show different temperature dependences with increasing temperature. The characteristic temperature of quenching is the 90 K served as a transitional temperature. Activation energy of Ea about 40 meV is obtained from the integrated intensity of the YL band using the Arrhenius formula.

Manipulating Solid-State Intramolecular Motion toward Controlled Fluorescence Patterns.

Molecules have limited mobility in the solid state because of the strong intermolecular interactions, and therefore, applications based on solid-state molecular motions are seldom explored. Herein, by manipulating the solid-state intramolecular motion of tetraphenylethylene (TPE) in a crystallizing polymer matrix, controlled fluorescent patterns with information storage and encoding functionality are developed. The intramolecular mobility of TPE can not only affect the fluorescence intensity but also determine the photocyclization activity, which can be tuned by surrounding polymer rigidity. The soft amorphous region in the semicrystalline polymer facilitates the intramolecular motion to achieve weak blue emission and high photocyclization activity, whereas the rigid crystalline phase restricts the intramolecular motion to give intense blue emission and low photoreactivity. Meanwhile, in the process of crystallization, the dynamic movement of the polymer chain in the crystal growth boundary layer further accelerates the intramolecular motions of TPE, allowing enhanced photoreactivity across crystalline and amorphous regions. The motion-dominated fluorescence allows TPE as a smart molecular robot to generate desired fluorescent patterns triggered by polymer crystallization. Our findings provide a correlation between microscopic molecular motions and macroscopic optical signals.

Amplified light harvesting for enhancing Italian lettuce photosynthesis using water soluble silicon quantum dots as artificial antennas.

Maximizing the utilization of the ultraviolet portion in the solar radiation spectrum has always been a goal for plant growth in order to minimize the harm and harvest the benefits. For this reason, fluorescent, amine-functionalized, and water-soluble silicon quantum dots (SiQDs) were fabricated with a mono-dispersed size of 2.4 nm. The SiQDs were used as artificial antennas to amplify the light harvesting ability and consequently enhance the photosynthesis in Italian lettuce. Upon ultraviolet excitation, the intense blue emission from the quantum dots matched very well to the absorption of the chloroplasts, allowing for the ultraviolet portion in solar radiation to be effectively utilized. The consumed optical energy enhanced the photosystem II activity, which made the amplification of photosynthesis possible. More importantly, in vivo, the quantum dots significantly promoted Italian lettuce seedling growth at concentrations below 30 mg L-1 on the root length, seedling height, and biomass by increasing the soluble sugar and water content by 49.8% and 40.9%, respectively. Interestingly, the chlorophyll a and b content increased to 41.0 and 114.8%, respectively, with no inhibition, even at the highest dose of 200 mg L-1. This study provides a new perspective on the use of quantum dots to amplify the utilization of ultraviolet light in agriculture.

Tetraphenylethylene-based color-tunable AIE-ESIPT chromophores

There has been growing interest in the design and development of tunable light emissive materials that have potential applications in lighting and displays. In this paper, we have incorporated the aggregation induced emission (AIE) with excited-state intramolecular proton transfer (ESIPT) process into one molecular skeleton for generation of color-tunable emitting materials. As expected, the high air/photo-stability of TPE-based asymmetric Schiff-base chromophores 1–2 displayed clear AIE characteristics and significant advantages in terms of tunable emission containing blue, warm white, as well as orange-red in solution. More importantly, all compounds 1–4 display brilliant colors by adjusting the intensity of blue and red emission in a mixture with a polymer in the solid state. This innovative research would provide a new, efficient channel for the discovery of well-organized full color emitting organic materials.

Crystal structure refinement, photoluminescence properties and energy transfer of multicolor tunable Ca2Al2SiO7:Tm3+, Dy3+ for NUV white-light-emitting diodes.

A promising phosphors Ca2Al2SiO7:Tm3+,Dy3+ were synthesized by conventional high temperature sintering. Phase identification, crystal structure refinement, luminescence properties, energy transfer mechanism of Tm3+→Dy3+, and CIE color coordinates were investigated systematically. The phase structure of prepared phosphors were confirmed by XRD analysis and structure refinement. From the results of photoluminescence, the CASO: Tm3+ phosphors showed intense blue light emission peaks at 454nm (the transition from 1D2 to 3F4), while CASO:Dy3+ phosphors exhibited predominant yellow light emission peaks at 581nm (the transition from 4F9/2 to 6H13/2), implying that the Dy3+ were located in the non-inverted symmetric site of the CASO host lattice. Meanwhile, the results exhibited that the optimal doping content of Dy3+ was 0.01, and the mechanism of concentration quenching was the nearest-neighbor ions interaction. The overlapped emission (Tm3+)/excitation (Dy3+) spectra, decay curves and the energy level scheme about CASO:Tm3+,Dy3+ confirmed the energy transfer of Tm3+→Dy3+. Moreover, by adjusting Tm3+/Dy3+ ions concentration, the intensities of yellow emission for Dy3+ and blue emission for Tm3+ could be adjusted to tune the emitting color of CASO:Tm3+, Dy3+. Excited by the most effective excitation wavelength at 355nm, the CIE coordinates (0.3422, 0.3262) of phosphor CASO:0.01Tm3+, 0.01Dy3+ was closest to the coordinates of white chromaticity (0.33, 0.33). Results indicate that the potential value of phosphors Ca2Al2SiO7:Tm3+,Dy3+ are used as a single-phase color-adjustable phosphors for NUV pumped white-LEDs.

Tailoring the properties of nebulizer spray pyrolysis coated FTO thin films through rare earth element terbium for optoelectronic applications

In optoelectronic device, transparent conducting oxide (TCO) acts as an electrode. In this work the rare earth element terbium (Tb) was doped with FTO by simple and inexpensive nebulizer spray pyrolysis (NSP) technique. Structural, optical end electrical properties were investigated for all the synthesized films. X-Ray diffraction (XRD) analysis confirmed that all the prepared films exhibited polycrystalline nature with tetragonal crystal structure and size of the crystalline reduced with increasing Tb concentration. Raman active doubly degenerate mode (Eg), IR active mode (Eu) and vibration mode (B2g) were found from Raman analysis. Atomic force microscope (AFM) images visualises the granular sized particle and the roughness of the Tb doped films. Elememental analysis spectrum exhibited Sn, O, F and Tb elements for 1.5 wt.% Tb doped thin film. Photoluminacence (PL) analysis revealed that UV, blue and green (visible) emission and UV emission intensity was reduced systamatically for the doped films. From UV–Vis analysis, highest optical transmittace were deduced for 1.5 wt.% Tb doped film. Reflectance, absorbance and band gap also been observed for the prepared films. Refractive index, extinction coefficient and dielectric constant values were decreased with increasing Tb doping concentration. High electrical conductivity and carrier concentration were measured using four probe hall effect system. Figure of merit value for the 1.5 wt.% Tb doped film is 1.5 × 10−3 Ω-1 and therefore the prepared film suits to be an electrode in optoelectronic devices.

Dual mode (upconversion and downshifting) behavior of Ho3+/Yb3+/Bi3+ co-doped YTaO4 phosphor and its application as a security ink

The Ho3+/Yb3+ co-doped YTaO4 phosphor has been synthesized in absence and presence of Bi3+ ion using high temperature solid state reaction method. X-ray diffraction (XRD) patterns confirm the pure phase formation of the synthesized materials. The vibrational behavior of the samples is studied by Fourier Transform Infrared (FTIR) spectroscopy, which suggests the phonon frequency of the material about 625 cm−1. The direct optical band gap of the synthesized phosphor has been calculated using UV–Vis absorption spectrum and the value is found to be 4.80 eV. However, the value of band gap is reduced in presence of Bi3+ ions (4.26 eV). Ho3+/Yb3+ co-doped YTaO4 phosphor shows intense green and weak red upconversion emissions on 980 nm excitation. Ho3+/Yb3+ co-doped YTaO4 phosphor sample also shows intense green and weak red emissions on 450 nm excitation. The downshifting emission is enhanced two to three times in presence of Bi3+ due to metal to metal charge transfer self activation of the host. However, the UC emission intensity almost remains unchanged even in presence of Bi3+. Bi3+ ion also shows an intense broad blue emission on UV excitation. The Ho3+/Yb3+ co-doped YTaO4 phosphor sample has been used for security ink applications in green region via 980 nm excitations and in blue region in presence of Bi3+ via UV (365 nm) excitation. Thus, the dual mode emission of this phosphor is applicable for security ink applications in two different regions. This material also permits one to get an intense tunable radiation from 350 to 650 nm on excitation with 342 nm. There are very few dye lasers, which emit intense tunable radiation in this wavelength region in such a wide wavelength range.

Multicolor upconversion emission of Ho3+ in single NaYF4 microrod

Lanthanide-doped upconversion nano/micro-materials exhibit superior and fascinating optical properties due to their unique 4f–4f transitions. They have been extensively investigated in various fields. Thus, studying the upconversion optical characteristic, especially for Er3+, Tm3+, and Ho3+ ions, is extremely important and useful. In this work, a strong upconversion emission with a candy-like fluorescent pattern has been discovered in a single NaYF4: Yb3+/Ho3+ microrod via confocal microscopy under NIR 980 nm excitation. When the Yb3+ ion-doped concentrations and the excitation power are increased, the Ho3+ ions show an increased blue emission intensity and high R/G ratio in single NaYF4 microrod, which is due to the cross-relaxation between Ho3+ ions. The corresponding upconversion emission behaviors and physical mechanisms have been studied on the basis of the spectral characteristics of Ho3+ ions and rate equations. Meanwhile, the candy-like emission pattern of single NaYF4 microrod is explained by establishing optical models, which because of the occurrence of fluorescence total reflection. The present study is of great importance in NaYF4 micro-materials doped with rare-earth ions, thereby providing new applications in optical anti-counterfeiting, 3D-displays, and wave-guides.

High quality, highly transparent Cu incorporated WO3 thin films suitable for blue LED application

Good crystalline Cu doped WO3 thin films are prepared using Radio Frequency (RF) magnetron sputtering and the films are characterised using various characterisation tools. Structural study using X-ray diffraction technique (XRD) and Micro-Raman Spectroscopy confirms the formation of monoclinic WO3 phase in all the films. The prepared films are preferentially oriented along a-axis and the film with 3 wt% Cu concentration show better crystalline quality. Morphological analysis (Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Microscopy (FESEM)) and elemental analysis (Energy Dispersive X-ray Spectroscopy (EDX)) show that Cu nanoparticles can act as seeding sites for the formation of bigger clusters in the films. The valence states of Cu in the prepared thin films are found to be +2 and 0 and/or +1 using X-ray Photoelectron Spectroscopic (XPS) study. The dip in the transmittance spectra and the corresponding enhanced absorption in the absorbance spectra around 620 nm region of 5 and 7 wt% Cu doped films detected using UV–Visible analysis can be attributed to localised surface plasmon resonance (LSPR) behaviour of Cu nanoparticles in these films. LSPR behaviour of Cu nanoparticles at higher Cu doped films suggests their suitability for improving the quantum efficiency of various photonic devices. A band gap renormalisation from 3.14 eV to 2.97 eV can be observed with increase in Cu incorporation concentration. Emission behaviour of Cu doped WO3 films are studied for their visible colour perception which show chromaticity coordinates corresponding to intense blue colour. The intense blue emission from Cu doped WO3 thin films suggests their suitability in blue light emitting diodes and in phosphor converted white light emitting diodes.

Blue-emitting Tm3+-doped Ca9NaGd2/3(PO4)7 phosphor with excellent thermal stability

A novel high thermal stability blue-emitting phosphor, Tm3+-doped Ca9NaGd2/3(PO4)7 in white light-emitting diodes (W-LEDs) has been fabricated via solid-state technique. The phase and optical properties were systemically investigated. The obtained phosphor presented an intense blue emission (centered at 456 nm) originated from the 1D2 → 3F4 transition of Tm3+ at λex = 360 nm. The energy transfer mechanism was judged as an electric multipole interaction with quenching concentration and critical distance in the Ca9NaGd2/3(PO4)7 host. Moreover, the emission intensity of synthesized phosphor maintained 97.5% of the value of room temperature at 420 K indicating excellent thermal stability. The results validated the Ca9NaGd2/3(PO4)7:Tm3+ phosphor can be utilized excellent blue-emitting candidate for W-LEDs.

Cathodoluminescence and photoluminescence from ZnS thin films deposited by novel seeded hydrothermal route

ZnS thin films have been synthesized by hydrothermal route on seeded glass and silicon substrates at various temperatures. The seeded substrates were prepared by RF magnetron sputtering technique. X-ray diffraction and transmission electron microscopic studies confirmed the good crystallinity and proper phase formation of the synthesized films. Synthesis temperature played an important role in improving crystallinity of the samples. Morphological information and the particle size were obtained from the field emission scanning electron microscopic measurement. Bonding information was obtained from FTIR studies. Determination of the band gap from the UV–vis-NIR spectrophotometric measurement showed that it decreased from 3.48 to 3.23 eV with increase of particle dimensions. The samples exhibited intense cathodoluminescence and photoluminescence while the blue emission intensity varied with increase in synthesis temperature.

Pyrene-based hyperbranched porous polymers with doped Ir(piq)2(acac) red emitter for highly efficient white polymer light-emitting diodes

Here, we designed and prepared a series of hyperbranched porous polymers constructed using fluorene branches and pyrene core, and all hyperbranched porous polymers exhibit intense blue fluorescence, good morphological stability, and high thermal stability. Further, it is found that the aperture sizes for hyperbranched porous polymers can be adjusted by simply changing the content of pyrene and fluorene in the synthesis process. When the feed ratios of pyrene in the total polymers is 15 mol%, the optimized aperture size was obtained, which is slightly larger than the maxlength of complementary red emitter Bis(1-phenylisoquinoline)(acetylacetonate)iridium (III) (Ir(piq)2acac), indicating the Ir(piq)2acac can well distributed in the apertures of hyperbranched porous polymers in co-doped film of Ir(piq)2acac and hyperbranched porous polymers. The fabricated polymer-light-emitting diode (PLED) with such co-doped film as light-emitting layer realizes good white emission with almost equal blue and red emission intensity from hyperbranched porous polymers and Ir(piq)2acac. The balanced electroluminescent (EL) spectra contribute to ideal Commission Internationale de l’Eclairage (CIE) coordinate of (0.326, 0.374) located at white light zone. In addition, the device also achieves high device performance with maximum luminance and current efficiency reaching 5369 cd/m2 and 8.35 cd/A, respectively. We believe that such porous-structure polymers have huge potential applications in the development of highly efficient white PLEDs with reducing production cost.