Quantum Efficiency Values Research Articles

Enhancing the ultraviolet photosensing properties of nickel oxide thin films by Zn–La co-doping

In this work, co-doping effects of transition (Zn) and rare-earth (La) elements on the crystalline structure, surface morphology, photoluminescence, optical and photosensing properties of NiO thin films are studied. NiO, NiO:Zn(1%), NiO:La(1%), and NiO:Zn(1%):La(1%) thin films are fabricated using the nebulizer spray pyrolysis (NSP) method. X-ray diffraction study revealed the cubic NiO structure of all the films. Photoluminescence (PL) spectra of thin films exhibit various emission peaks centered at the wavelengths of 387, 414, 437, 451, 477, and 521 nm. The optical bandgap energy ( E g ) values are found to be 3.46, 3.43, 3.39 and 3.33 eV for NiO, NiO:Zn(1%), NiO:La(1%) and NiO:Zn(1%):La(1%) thin films, respectively. The fabricated (Zn, La) co-doped NiO i.e., NiO:Zn(1%):La(1%) photo-detector exhibits highest responsivity ( R ), external quantum efficiency (EQE) and detectivity ( D *) values of 0.50AW -1 , 169% and 14.5 × 10 9 Jones, respectively as compared to NiO, NiO:Zn(1%) and NiO:La(1%) photo-detectors. The present study revealed that the transition and rare-earth elements co-doping can be an effective approach for tuning the various physical properties of semiconducting oxide films.

Extremely High Power Efficiency Solution‐Processed Orange‐Red TADF OLEDs via a Synergistic Strategy of Molecular and Device Engineering

AbstractThe development of high‐performance, solution‐processed, orange‐red organic light‐emitting diodes (OLEDs) based on thermally activated delayed fluorescence (TADF) emitters is a challenging endeavor. In this study, two orange‐red TADF emitters, namely 2DMAC‐DBP‐2tBuCz and 2SPAC‐DBP‐2tBuCz, are developed by a novel donor–acceptor–functional‐group (D‐A‐R) molecular design strategy. This design makes the molecules highly soluble and inhibits concentration quenching of excitons, rendering the emitter suitable for use in devices with high concentration to boost their performance. The solution‐processed, orange‐red OLEDs manufactured in this study achieve a state‐of‐the‐art maximum external quantum efficiency (EQEmax) value of 23.7% and an extremely high maximum power efficiency (PEmax) of 48.8 lm W−1, which is nearly twice higher than the previously reported best value (27.1 lm W−1). Therefore, the collaboration of molecular engineering and sophisticated device design provides a novel method for extremely low power consumption solution‐processed OLEDs.

Efficient Stable Green Hybrid Light-Emitting Devices Using Cathode Interlayer

Hybrid photoconductive materials of SnO2 doped organic materials (SnO2:PBA-PA and SnO2:PFN; PBA-PA, 2,9-bis(1-benzylpiperidinyl)-5,6,12,13-tetrachloroanthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10-(2H,9H)-tetraone; and PFN, 9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)) have been employed as the photoconductive interlayer in efficient hybrid organic light-emitting diodes (OLEDs). The absorption of the SnO2:PBA-PA interlayer reduced the emission intensity at 562 nm due to spectral overlap of the absorption of PBA-PA with the electroluminance (EL) of iridium(III) bis(4,5-dimethyl-1-(naphthalene-1-carbonitrile)-1H-imidazolato-N,C2′)(acetyl acetonate) (Ir(DNC)2(acac)). The fabricated OLEDs having the configuration of indium tin oxide (ITO)/cathode interlayers SnO2/SnO2:PBA-PA/SnO2:PFN/Ir(DNC)2(acac)/MoO3/Al show luminance (L) values of 4289/18056/23135 cd/m2, current efficiency (CE) values of 2.5/15.3/16.8 cd/A, power efficiency (PE) values of 1.1/7.4/8.6 lm/W, and external quantum efficiency (EQE) values of 7.3/14.3/17.0% at 4.6/3.0/2.9 V. The SnO2:PBA-PA based device exhibit increased luminance (ZL) of 22.0%, ZCE of 8.9%, ZPE of 14.0%, and ZEQE of 15.9% compared with SnO2:PFN based device. Compared with the SnO2 device, the SnO2:PBA-PA based device exhibited increased luminance (ZL) of 81.5%, ZCE of 85.1%, ZPE of 87.2%, and ZEQE of 57.1% with reduction in turn-on voltage from 4.6 to 2.9 V. These interlayers show increased conductivity due to effective electron mobility which enhances the electron–hole recombination efficiency in the emissive layer and leads to improvement of the performances of devices. The novel photoconductive interlayers (SnO2:PBA-PA and SnO2:PFN) decreased the energy barrier (cathode interlayer:light-emitting layer) results in the decrease of the turn-on voltage. Our research findings demonstrate that the insertion of a cathode interlayer opens up a new way to enhance the device efficiency.

High performance low-bandgap (0.8 eV) single junction GaInNAsSb solar cells incorporating Au-based back surface reflectors

Low-bandgap GaInNAsSb single junction solar cells incorporating a planar Au back surface reflector for enhancing the photocurrent generation are reported. In particular, a 700 nm thick GaInNAsSb junction with a bandgap of 0.78 eV (corresponding to 6.2% N) incorporating the back reflector exhibited a short-circuit current density of 15.2 mA/cm2 for AM1.5D (1000 W/m2) illumination, when placed underneath a GaAs-filter mimicking the operation of a multijunction architecture. The corresponding external quantum efficiency represents the highest external quantum efficiency reported so far for dilute nitride solar cells with bandgaps below 0.8 eV. Electrical simulations reveal that the relatively high value of the quantum efficiency is attributed to a low p-type carrier concentration and partially to the varying doping level in the GaInNAsSb region. Moreover, the absorption coefficients for low-bandgap GaInNAsSb materials are estimated and used in a comprehensive optical analysis to understand the photon harvesting performance of the solar cells with reflector. The analysis reveals incomplete absorption in the GaInNAsSb layers for the double-pass configuration enabled by the planar back reflector pointing to the need for deploying more advanced structured reflectors. However, the structures exhibited high collection efficiencies laying the foundation for further improvements of the quantum efficiency values. Moreover, the low-bandgap dilute nitride solar cells show potential to meet the current-matching requirements in next-generation multijunction devices with five or more junctions, thus being a prospective alternative for replacing Ge as the bottom junction.

Spectral characteristics of Tb3+ doped ZnF2–K2O–Al2O3–B2O3 glasses for epoxy free tricolor w-LEDs and visible green laser applications

In the current work, a series of Zinc Potassium Alumino fluoroborate (ZKAlFB) glasses doped with different concentrations of Terbium ions (Tb3+) were synthesized by employing the melt-quench technique. The spectroscopic properties of the as-prepared glass samples were examined using characterization techniques like XRD, FT-IR, DSC, UV–vis–NIR absorption and emission to unlock their utility in photonic devices. Absorption spectral information was used to determine the nature of bonding between Tb3+ ions and its surrounding ligands. FT-IR spectral information recorded for an undoped glass has been used to understand various functional groups present in the as-prepared ZKAlFB glass. The DSC thermogram was used to estimate glass thermal stability (ΔT) and transition temperature (Tg) of the as-prepared ZKAlFB glass. The Judd-Ofelt (J-O) intensity parameters estimated from absorption spectral data are correlated with the emission spectral profiles to estimate radiative properties. The photoluminescence (PL) intensity of the as-prepared ZKAlFBTb glasses is found to be maximum for 1 mol% of Tb3+ ions and beyond decreases showing concentration quenching. Using PL spectral data, the CIE color coordinates, and Correlated Color Temperature (CCT) values were evaluated to understand the suitability of the as-prepared glasses for green color emitting photonic devices. The experimental lifetime values estimated from the decay profiles are decreasing with elevation in Tb3+ ion concentration due to energy transfer through the cross-relaxation process. Quantum efficiency (η), emission cross-section (σse), CIE and CCT values obtained for 1 mol% Tb3+ ions doped ZKAlFB glass demonstrates its superiority in fabricating epoxy free tricolor w-LEDs and visible green lasers.

Novel cerium-based MOFs photocatalyst for photocarrier collaborative performance under visible light

A novel cerium-based metal–organic framework crystal (Ce-TBAPy) was developed via a one-pot solvothermal method. Interestingly, the Ce-TBAPy photocatalyst material demonstrated an enhanced collaborative photoredox performance in terms of acetaldehyde degradation and water reduction, and the photoreaction rates of Ce-TBAPy shown about 5.06-times and 3.94-times higher, respectively, than those when untreated H4TBAPy was used. A significant finding is that the apparent quantum efficiency value of Ce-TBAPy for CO2 generation from CH3CHO decomposition performs 5.12% at 420 nm. The accumulation of abundant separated holes on the pyrene macrocycles could oxidize CH3CHO to CO2 easily. Meanwhile, cerium integration with TBAPy4− ligands to form a π-conjugated construction further resulted in sufficient photoinduced electrons and exhibited effective interfacial charge separation, which harvesting the reduction of H2O to H2 efficiently. The electronic localization influence arising from the formation of –COO-Ce functional groups in Ce-TBAPy and the direction of electron migration in the photocatalytic system were further confirmed by DFT calculation. This work provides an effective strategy to obtain rare earth-based MOF photocatalysts with dual redox functions and holds promise for advancing the prospect of using MOF materials to convert solar energy into chemical energy.

Enhanced red emission in Eu3+ ions doped ZnO-Al2O3-BaF2-CaF2-B2O3 glasses for visible laser applications

Europium ions doped Oxy-Fluoro-Borate glass samples (OFB) were synthesized through the melt-quench mechanism. In order to analyze the lasing properties; absorption, photoluminescence (PL) excitation, PL emission, and PL decay curve spectral measurements were done. For europium ions doped OFB glasses, the Judd-Ofelt (J-O) parameters were evaluated from the PL spectra instead of absorption spectral data. The obtained J-O parameters follow the same trend Ω2>Ω4 for all the titled glasses. The PL spectra of all the glasses possess an intense peak in the reddish region at 612 nm. In europium doped OFB glasses, the concentration quenching is not observed up to 2.0 mol%. From the decay profiles, experimental lifetimes were measured and they are used to evaluate the quantum efficiency. Of all the glasses OFBEu20 glass has the highest values of quantum efficiency and stimulated emission cross-section. The evaluated CIE coordinates of these glasses also fall in the reddish region which can be confirmed through the con-focal images. Hence OFBEu20 glass is aptly considered as a good optical material for red color laser emission.

Improved optoelectronic properties of Yttrium co-doped CdO:Zn thin films fabricated by nebulizer spray pyrolysis method for TCO applications

To understand the effect of Yttrium (Y) co-doping with CdO:Zn towards optoelectronics applications, the thin films were coated by the nebulizer spray pyrolysis route. The microstructural studies (XRD) reveals that the crystallite size decreases from 20 to 15 nm with the increase of Y concentrations. The surface topography of the films has been strongly influenced by the Y doping which is evident from the AFM images. The presence of Cd, O, Zn, and Y has been confirmed through the EDX spectrum. The transparency is higher (81%) for the CdO:Zn-Y(1.5%) film. The decreasing trend in the values of the optical dielectric constant is observed with increases in yttrium content. The enhancement in the carrier concentration (12 × 1020cm−3) and reduction in the electrical resistivity (8.4 × 10−4Ωcm) have been observed for the CdO:Zn-Y(1.5%) film via the Hall-effect measurements. In addition, the heterojunction p-Si/n-CdO:Zn-Y(1.5%) photodiode was fabricated to understand the optical sensing properties. The current values of the fabricated photodiode are found to enhance as the intensity of the illumination increases from1.0 to 3.0 mW cm−2. Moreover, the photodiode exhibits the highest responsivity, detectivity, and external quantum efficiency value of 1.45 AW−1, 6 × 109 Jones, and 339%, respectively with excellent switching speeds. This work provided a guideline to develop a TCO layer and photodiode towards the applications of optoelectronic-based devices.

Improved photocurrent properties of La doped CuO thin films coated by nebulizer spray pyrolysis method for photosensor applications

In this study, pure and La of various concentrations (0.5, 1.0, 1.5, 2.0, and 2.5 wt.%) doped CuO thin films were produced by means of the NSP technique to be used as UV photodetection applications. Various physicochemical investigations such as XRD, SEM, PL, UV–Vis, and current-voltage (I–V) characteristics have been conducted to inspect the role of La in the grown films. X-ray diffraction data confirm the single cubic crystal structure and the size of crystallites shrinkages from 22.6 to 19.4 nm. SEM photo shows the formation of triangular prismic shape like morphology. The spectroscopic studies show that the added La impurity promotes their absorption level in the UV region and redshift the optical bandgap from 2.07 to 1.81 eV. Photoluminescence spectral analysis confirms the presence of oxygen vacancies at 413 nm. Upon exposure to a UV light source (λ = 365 nm) the fabricated La-doped CuO thin films offered a better photo-responsivity, detectivity, and external quantum efficiency value of 1.63 × 10−1 AW−1, 1.75 × 1010 Jones, and 107% respectively. Our results provide a guideline to design high-performance UV photodetectors.

Color-Stable and High-Efficiency Blue Perovskite Nanocrystal Light-Emitting Diodes via Monovalent Copper Ion Lowering Lead Defects.

Light-emitting diodes using metal halide perovskite (PeLEDs) exhibit a strong potential for emerging display technologies due to their unique optoelectronic characteristics. However, for blue emission PeLEDs, there remains a huge challenge to achieve high performance, an issue that has been addressed in their red and green counterparts. The community is circumventing the challenges in synthesizing stable, high-quantum-efficiency, and low-defect-density blue emitters. Here, a facile strategy that replaces Pb by adding a monovalent ion Cu+, in this case into CsPbClBr2 perovskite, is carried out. This decreases the Pb dangling bonds and increases the radiative recombination for the enhancement of blue emission. The nanoparticles obtained by this method maintain a blue emission at 479 nm. The photoluminescence quantum yield is 2 times higher than the pristine analogue. The corresponding perovskite nanocrystal (PNC) LEDs achieve stable electroluminescence spectrum at high brightness. Simultaneously, the optimal blue PNC LEDs obtain the maximum values of luminance and external quantum efficiency of 1537 cd m-2 and 3.78%, respectively. And the device realizes typical blue light CIE chromaticity coordinates of (0.098, 0.123). Our work reveals that the substitution of Pb by heterovalent ions significantly decreases nanocrystal defects, which will pave the way of perovskite LEDs for practical applications in the future.

Bright and Efficient Pure Red Perovskite Nanocrystals Light‐Emitting Devices via In Situ Modification

AbstractAlthough light‐emitting devices (LEDs) based on metal halide perovskite nanocrystals (PNCs) developed rapidly in recent years, the luminance of pure red LEDs with the Rec. 2020 standard Commission Internationale de l'Eclairage 1931 color coordinates of (0.708, 0.292) cannot meet the requirement of outdoor display. Herein, a facile in situ modification strategy is proposed to prepare the efficiently luminescent CsPb(Br/I)3 PNCs, where metal bromides are used to create a halide‐rich environment and inhibit the formation of nonradiative surface defects. Synchronously, appropriately increased surface ligands improved the effective exciton confinement. Hence, the modified CsPb(Br/I)3 PNCs exhibited a high photoluminescence quantum yield of 92.0%. Additionally, the electrical conductivity is improved due to the increased hole mobility, and the Auger process is inhibited caused by balanced carrier mobilities. Consequently, LEDs based on the modified CsPb(Br/I)3 PNCs exhibited a maximum luminance of 11233 cd m−2 with the pure red color coordinate (0.704, 0.292) and a peak external quantum efficiency value of 13.2%. Furthermore, the luminance reached 5198 cd m−2 under the driving voltage of 4.4 V. This is the first study to realize a pure red PNC LED with high luminance under low bias, which can meet the requirement of outdoor display.

Red Phosphorescent Carbon Quantum Dot Organic Framework-Based Electroluminescent Light-Emitting Diodes Exceeding 5% External Quantum Efficiency.

Carbon quantum dots (CQDs) have developed into prospective nanomaterials for next-generation lighting and displays due to their intrinsic advantages of high stability, low cost, and environmental friendliness. However, confined by the spin-forbidden nature of triplet state transitions, the highest theoretical value of external quantum efficiency (EQE) of fluorescent CQDs is merely 5%, which fundamentally limits their further application in electroluminescent light-emitting diodes (LEDs). Soluble phosphorescent CQDs offer a means of breaking the shackle to achieve efficient monochromatic electroluminescence, especially red emission, which is a pivotal constituent in full-color displays. Here, the synthesis of red (625 nm) phosphorescent carbon quantum dot organic frameworks (CDOFs) with a quantum yield of up to 42.3% and realization of high-efficiency red phosphorescent electroluminescent LEDs are reported. The LEDs based on the CDOFs exhibited a red emission with a maximum luminance of 1818 cd m-2 and an EQE of 5.6%. This work explores the possibility of a new perspective for developing high-performance CQD-based electroluminescent LEDs.

Fabrication of novel Cu2WS4/NiTiO3 heterostructures for efficient visible-light photocatalytic hydrogen evolution and pollutant degradation

The design and development of efficient and durable catalysts with visible-light response for photocatalytic hydrogen production and pollutants degradation is considered as one of the most challenging tasks. In present work, a novel Cu2WS4/NiTiO3 (abbreviated as × CWS/NTO; x = 0.25, 0.50, 0.75 and 1.00) composite was prepared via a facile electrospinning/calcination technique along with a convenient hydrothermal method. The as-prepared CWS/NTOcomposite was composed of 2D CWS nanosheets and 1D NTO nanofibers manifested by SEM and TEM images. The results of XPS verified the interfacial interaction between CWS and NTO, confirming the heterojunction formation in CWS/NTOcomposite. Photocatalytic tests demonstrated as-prepared CWS/NTO catalysts exhibited outstanding and stable photocatalytic performances for H2 production and pollutants degradation under visible light (λ > 420 nm) irradiation. Specially, 0.50 CWS/NTO sample displayed the highest H2-evolution activity of 810 μmol·g−1·h−1 with the apparent quantum efficiency (AQE) value of 1.65 % at 420 nm. Additionally, it also exhibited the optimal photodegradation properties with the rate constants of 0.030, 0.413 and 0.028 min−1 for TC, RhB and Cr(VI), respectively. The excellent catalytic activities could be attributed to the enhanced visible-light adsorption, high specific surface area and efficient separation of photogenerated charge carriers. The ESR tests and free radicals capturing experiments confirmed that ·O2– and h+ were primary active species for TC/RhB degradation. Eventually, the probable catalytic mechanism was put forward and detailly analysed. The present work provides perspectives of rational design on NiTiO3-based catalysts with superior photocatalytic performance for energy regeneration and environmental remediation.

Electrical crosstalk analysis in a pinned photodiode CMOS image sensor array.

In this paper, a complete investigation and 2D simulation of electrical crosstalk in a setup with three neighboring pinned photodiode complementary metal-oxide-semiconductor (CMOS) image sensor pixels are performed. Electrical crosstalk characterization as a function of pixel size and epitaxial layer doping concentration is presented. The simulation results in constant epitaxial layer doping concentration show that the ratio of external quantum efficiency to electrical crosstalk is linear with respect to pixel size. In the pixel size of 3.7 µm, the turning point in the correlation trend between external quantum efficiency and electrical crosstalk from a small pixel size to a large one occurs. In addition, the simulation results show the optimal values of external quantum efficiency and electrical crosstalk occurs at 1×1014 (cm-3) in a constant pixel size. Moreover, the ratio of external quantum efficiency to the electrical crosstalk decreases linearly with respect to the epitaxial layer doping considering above 1×1014 (cm-3).

Ageing mediated silicon suboxide interlayer growth in porous silicon: p-Si heterostructured metal-semiconductor-metal device for enhanced UV-visible photodetection

Present work reports development of silicon oxide within metal-semiconductor-metal Schottky contact photodiode from Al: porous silicon (PS):p-Si heterojunction mediated by ageing to investigate its effect on its light sensing property. Oxide layer formation is achieved by auto-ageing. Formation of silicon suboxide (SiOx, x≤2) layers on PS:p-Si surface in aged heterostructure is confirmed from elemental energy dispersive X-ray analyses. X-ray diffraction patterns of as-prepared and aged heterostructure show broadening of strong (400) reflection peak compared to that of bare p-Si one due to nanocrystallite formation. PS crystallite size is found to be ∼45 nm. Raman spectra of as-prepared and aged heterostructure for an excitation wavelength of 633 nm show intense, broad and asymmetric peak at 519 cm−1 along with c-Si related peak at 522 cm−1. Photoluminescence spectra of as-prepared heterostructure shows red shift of ∼15 nm of the strong characteristic emission peak from 590 to 605 nm for increasing excitation wavelengths in the range of 275–400 nm. Aged heterostructure for fixed excitation wavelength of 275 nm shows strong characteristic emission peak at 590 nm along with weak emission peaks at 470 and 500 nm related to defect levels present in SiOx layers developed on PS surface. Ideality factor and Schottky barrier height for the aged device show enhancement of 12.4 and 0.15 eV respectively over the as-prepared one. The enhancement in maximum photo to dark current ratio of the aged device is 4.8, whereas maximum values of responsivity and external quantum efficiency improves up to 0.47 AW−1 and 145 % respectively for illumination wavelength of 400 nm for bias of -3 V. In contrast, however, the response and recovery times remain unchanged at 0.16 and 0.24 s respectively. These results suggest application potential of the device in the optoelectronic field particularly as an efficient ultraviolet-visible photo-detector.

Deep-Red Perovskite Light-Emitting Diodes Based on One-Step-Formed γ-CsPbI3 Cuboid Crystallites.

Inorganic CsPbI3 perovskite with high chemical stability is attractive for efficient deep-red perovskite light-emitting diodes (PeLEDs) with high color purity. Compared to PeLEDs based on ex-situ-synthesized CsPbI3 nanocrystals/quantum dots suffering from low conductivity and efficiency droop under high current densities, in situ deposited 3D CsPbI3 films from precursor solutions can maintain high conductivity but show high trap density. Here, it is demonstrated that introducing diammonium iodide can increase the size of colloids in the precursor solution, retard the phase-transition rate, and passivate trap states of the in-situ-formed cuboid crystallites. The PeLED based on the one-step-formed 3D CsPbI3 cuboid crystallite films shows a peak external quantum efficiency (EQE) value up to 15.03% because of the high conductivity and reduced trap states. Furthermore, this one-step method also has a wide processing window, which is attractive for flow-line production of large-area PeLED modules. The fabrication of a 9 cm2 PeLED that exhibits a peak EQE of 10.30% is successfully demonstrated.

Quantum efficiency, intrinsic emittance, and response time measurements of a titanium nitride photocathode

The photoemission properties of photocathodes affect the ultimate performance of electron accelerator based facilities and the cost. Several major properties of titanium nitride (TiN) irradiated by ultraviolet femtosecond laser pulses were studied. Specifically, the quantum efficiency and intrinsic emittance were measured, and the response time was estimated indirectly. For photon energies higher than the work function, quantum efficiency values of $7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}--5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ were obtained. The measured intrinsic emittance was $0.54\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ for the typical wavelength of 266 nm (4.66 eV). When the photon energy was lower than the work function, two-photon photoemission appeared, and the intrinsic emittance increased with the laser intensity. At photon energies of higher than and slightly lower than the work function, the intrinsic emittance ranged from 0.28 to $0.60\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ and tended toward a minimum constant of $0.28\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{mm}$ if only single-photon photoemission was considered. The response time of TiN was proven to be close to that of gold by comparing the transverse expansion of electron beams under space charge force for the irradiated photon energy higher than the work function. The autocorrelation measurement of the photoemission of TiN and gold were performed, and a comparison of these results indicated that the two-photon photoemission of TiN excited by a photon energy slightly lower than the work function was prompt.

Crystal chemistry and photoluminescent investigation of novel white light emanating Dy3+ doped Ca9Bi(VO4)7 nanophosphor for ultraviolet based white LEDs

A novel series of white light emitting Ca 9 Bi (1− x ) Dy x (VO 4 ) 7 nanophosphor has been prepared via urea-assisted solution combustion method for the very first time. Structural aspects of the synthesized nanophosphors are investigated by means of X-ray diffraction patterns. The Rietveld refinement performed on host Ca 9 Bi(VO 4 ) 7 and optimal luminescent composition Ca 9 Bi 0.80 Dy 0.20 (VO 4 ) 7 authenticate crystallization in trigonal lattice and space group as R 3 c (161). The emission spectra exhibit peaks due to 4 F 9/2 → 6 H 11/2, 13/2, 15/2 characteristic transitions of Dy 3+ ions on excitation at 389 nm wavelength in ultraviolet region. The band gap for Ca 9 Bi(VO 4 ) 7 has been estimated to be 3.27 eV. The dipole-dipole type interactions are responsible for concentration quenching phenomena in trivalent dysprosium doped Ca 9 Bi(VO 4 ) 7 post 20 mol% composition of dopant ions. The intrinsic lifetime value (0.418 ms) and non-radiative rate (132.27 s −1 ) are determined by employing Auzel's model. The chromaticity coordinates ( x = 0.288, y = 0.338), correlated color temperature (7760 K) and quantum efficiency value (95%) indicate towards a cool and efficient white light emanating Ca 9 Bi 0.80 Dy 0.20 (VO 4 ) 7 nanophosphor. The crystal and optical properties of the prepared nanophosphor vividly define its potential usage as ultraviolet triggered white light emitting source for lighting applications.

7,7-Dimethyl-9-(10-phenylanthracen-9-yl)-7H-Benzo[b] Fluoreno[3,4-d]Thiophene Derivatives for Blue Fluorescent Organic Light-Emitting Diodes.

In this study, we designed and synthesized two blue fluorescence materials using 7,7-dimethyl-9-(10-phenylanthracen-9-yl)-7H-benzo[b]fluoreno[3,4-d]thiophene substituted anthracene derivatives. To characterize their electroluminescent properties, we fabricated the OLED devices using these two emitting materials. Particularly, a device using 7,7-dimethyl-9-(10-phenylanthracen-9-yl)-7Hbenzo[ b]fluoreno[3,4-d]thiophene showed maximum values of luminous efficiency, power efficiency, and external quantum efficiency of 2.42 cd/A, 1.48 lm/W, 3.08% at 20 mA/cm2, respectively with CIE (x, y) coordinates of (0.15, 0.09) at 8.0 V.

Mechanochromic and thermally activated delayed fluorescence dyes obtained from D–A–D′ type, consisted of xanthen and carbazole derivatives as an emitter layer in organic light emitting diodes

In this study, we designed, engineered and investigated two new thermally activated delayed fluorescence (TADF) dyes obtained from D–A–D′ type, consisted of 2-(9H-carbazol-9-yl)-3-(3-methoxy-9H-carbazol-9-yl)-9H-xanthen and 2-(3,6-di-tert-butyl-9H-carbazol-9-yl)-3-(3-methoxy -9H-carbazol-9-yl)-9H-xanthen. In these dyes, xanthen derivative and carbazole derivatives have played important roles as an acceptor and two unsymmetrical donor units. In addition, the photophysical properties of these dyes were evaluated by the UV–VIS absorption, photoluminescence spectroscopy and photoluminescence decay lifetime analysis in solution, initial dye, non-doped and doped solid state (neat–film) at different temperatures and under the vacuum-ambient. Substitution's strong effect of the donor units was impressive; where, the dyes' ionization potential values were achieved as 5.53 and 5.62 eV. The charge mobility measurements of dyes were carried out using two different methods of spacecharge–limited current (SCLC) and time of the flight (TOF). Appropriate extracted results proved dyes' promising application as an emitter layer in organic light emitting diodes (OLEDs), through the photophysical properties, aggregation induced emission enhancement (AIEE) phenomenon, and high intensity of emission spectrum spanning the large part of visible area and good thermal stability. The solution process and physical evaporation deposition (PVD) procedure were tandemly performed in order to coat the layers and fabricate non-doped and doped OLEDs. The low turned on voltage' values of OLEDs were recorded in the range of 4.08 to 5.31 V. Furthermore, the maximum values of brightness, current, power and external quantum efficiency were achieved as 72565 cd/m2, 37.32 cd/A, 20.99 lm/W and 13.41%, respectively.