Application In Light-emitting Diodes Research Articles

Single-crystalline GaN microdisk arrays grown on graphene for flexible micro-LED application

We report the growth of single-crystalline GaN microdisk arrays on graphene and their application in flexible light-emitting diodes (LEDs). Graphene layers were directly grown on c-sapphire substrates using chemical vapor deposition and employed as substrates for GaN growth. Position-controlled GaN microdisks were laterally overgrown on the graphene layers with a micro-patterned SiO2 mask using metal–organic vapor-phase epitaxy. The as-grown GaN microdisks exhibited excellent single crystallinity with a uniform in-plane orientation. Furthermore, we fabricated flexible micro-LEDs by achieving heteroepitaxial growth of n-GaN, In x Ga1−x N/GaN multiple quantum wells, and p-GaN layers on graphene-coated sapphire substrates. The GaN micro-LED arrays were successfully transferred onto bendable substrates and displayed strong blue light emission under room illumination, demonstrating their potential for integration into flexible optoelectronic devices.

Thienothiophene-based organic light-emitting diode: synthesis, photophysical properties and application.

A donor-π-acceptor (D-π-A)-type pull-push compound, DMB-TT-TPA (8), comprising triphenylamine as donor and dimesitylboron as acceptor linked through a thieno[3,2-b]thiophene (TT) π-conjugated linker bearing a 4-MeOPh group, was designed, synthesized, and fabricated as an emitter via a solution process for an organic light-emitting diode (OLED) application. DMB-TT-TPA (8) exhibited absorption and emission maxima of 411 and 520 nm, respectively, with a mega Stokes shift of 109 nm and fluorescence quantum yields both in the solid state (41%) and in solution (86%). The optical properties were supported by computational chemistry using density functional theory for optimized geometry and absorption. A solution-processed OLED was fabricated using low turn-on voltage, which had performances with maximum power, current, and external quantum efficiencies of 6.70 lm/W, 10.6 cd/A, and 4.61%, respectively.

Theoretical study on the influence of substitution position on the luminescence properties and charge transfer characteristics of thermally activated delayed fluorescent molecules

Thermally active delayed fluorescence (TADF) molecules have potentially applications in organic light-emitting diodes (OLEDs) and biomedical sensing. Although TADF emitters have witnessed a rapid development, it remains challenging to study the relationship between molecular structures and luminescence properties as well as carrier mobility transfer properties in theory. In this work, the photophysical properties and luminescence mechanisms of isomers TPA-APQDCN-C (donors at para-position) and TPA-APQDCN-Y (donors at ortho-position) were studied based on density functional theory (DFT) and thermal vibration correlation function (TVCF) method. The results showed that both TPA-APQDCN-C with para-substituted donor and TPA-APQDCN-Y with ortho-substituted donors exhibit red emission in toluene and crystal state. Furthermore, compared to ortho-substituted donors, para-substituted donors promote a redshift in emission wavelength. In addition, the fluorescence efficiencies of TPA-APQDCN-C is obviously higher than that of TPA-APQDCN-Y due to its larger radiative rate and less non-radiative decay rate. Besides, para-substitution (TPA-APQDCN-C) leads to the smaller energy gap between S1 and T1 and the larger spin–orbit coupling (SOC) constant, which is beneficial for increasing the reverse crossing intersystem (RISC) rates. In addition, the carrier mobilities are studied based on the kinetic Monte Carlo simulations. The calculations show that TPA-APQDCN-C are more beneficial for the transfer of holes compared to TPA-APQDCN-Y. This study reveals TPA-APQDCN-C with donors at para-position has a better TADF properties and hole transfer ability, which holds guiding significance for the design of TADF devices with high luminescence efficiency and rapid hole transfer.

Synthesis and study of luminescence properties of a deep red-emitting phosphor K2 LiAlF6 :Mn4+ for plant cultivation.

Light is the most important component in plant growth and development. This study synthesised a novel Mn4+ -doped K2 LiAlF6 red-emitting phosphor using the coprecipitation method. We observed that on addition of dopant Mn4+ ions to the host K2 LiAlF6 , its phase changed from rhombohedral to cubic due to the change in the lattice position of the atoms. When the atoms are excited at 468 nm, the K2 LiAlF6 :Mn4+ phosphor exhibited a red emission band ranging from 630 to 700 nm, centred at 638 nm, which matched well with the absorption spectra of phytochrome PR. The critical quenching content of Mn4+ ions was ~3mol%. The critical distance between Mn4+ ions was determined to be 19.724 Å, and non-radiative energy transfer among the nearest-neighbour Mn4+ ions was the mechanism used for the concentration quenching effect. The Commission International de l'Eclairage (CIE) chromaticity coordinates of the K2 LiAlF6 :0.03 Mn4+ sample were (x = 0.7162, y = 0.2837). The luminescence mean decay time was calculated to be 8.29 ms. These results demonstrated the promising prospect of K2 LiAlF6 :Mn4+ as a red-emitting phosphor for application in red light-emitting diodes for plant cultivation.

Phase distribution management for high-efficiency and bright blue perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) perovskite materials have attracted significant attention for application in light-emitting diodes (PeLEDs) due to their unique optical characteristics and extraordinary performance. The inherent multi-quantum well structure will generate a strong quantum confinement effect which is beneficial for the blue emission. However, the efficiency and stability of the quasi-2D blue PeLEDs lag behind their red and green counterparts, which prevents the further commercial application of the PeLEDs. The performance of quasi-2D blue PeLEDs was limited on account of the inefficient phase distribution management, which causes an inefficient energy transfer and severe non-radiative recombination. Herein, we employ guanidine thiocyanate (GASCN) as the pre-deposited film at the bottom of the perovskite film to manage the phase distribution of the PBA2Csn−1PbnBr3n+1 quasi-2D perovskite film (where n is the number of [PbBr6]4- sheets, and PBA is phenylbutylammonium). The pre-deposited GASCN can not only inhibit the small n-phase (i.e., n = 1: PBA2PbBr4, and n = 2: PBA2CsPb2Br7) but also avoid the undesired emission redshift from the over-growth of the large n-phase as well as passivate defects of the quasi-2D perovskite film, which accelerates energy transfer efficiently, strengthens the carrier transport, and enhances the luminous efficiency. As a result, the optimized device demonstrated the highest external quantum efficiency (EQE) of 16.40% and a maximum luminance of 8290 cd m−2. This strategy provides a new pathway to accurately manage phase distribution of quasi-2D perovskite achieving the high efficiency in blue PeLEDs.

Efficient Visible-Light-Activated Ultra-Long Room-Temperature Phosphorescence Triggered by Multi-Esterification.

The development of ultra-long room-temperature phosphorescence (UL-RTP) in processable amorphous organic materials is highly desirable for applications in flexible displays, anti-counterfeiting, and bio-imaging. However, achieving efficient UL-RTP from amorphous materials remains a challenging task, especially with activation by visible light and a bright afterglow. Here we report a general and rational molecular-design strategy to enable efficient visible-light-excited UL-RTP by multi-esterification of a rigid large-plane phosphorescence core. Notably, multi-esterification minimizes the aggregation-induced quenching and accomplishes a 'four birds with one stone' possibility in the generation and radiation process of UL-RTP: i) shifting the excitation from ultraviolet light to blue-light through enhancing the transition dipole moment of low-lying singlet-states, ii) facilitating the intersystem crossing process through the incorporation of lone-pair electrons, iii) boosting the decay process of long-lived triplet excitons resulting from a significantly increased transition dipole moment, and iv) reducing the intrinsic triplet nonradiative decay by substitution of high-frequency vibrating hydrogen atoms. All these factors synergistically contribute to the most efficient and stable visible-light-stimulated UL-RTP (lifetime up to 2.01 s and efficiency up to 35.4 % upon excitation at 450 nm) in flexible films using multi-esterified coronene, which allows high-tech applications in single-component time-delayed white light-emitting diodes and information technology based on flashlight-activated afterglow encryption.

A study on the impact of [BO33−], [PO43−] and [SO42−] ions in normal cubic structures via structural and photoluminescence properties of Y2O3:Eu3+ phosphors

A series of Y2O3-AG: Eu3+ (where AG = Anionic Groups [PO43−, SO42− and BO33−]) nanophosphors were synthesized via a chemical combustion method and their structural and photoluminescence properties were investigated. The crystal structure and the surface morphology studies were analysed through the X-Ray powder diffraction (XRPD), Field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The XRD results showed that undoped Y2O3 phosphors crystalized in a cubic crystal structure, while the Y2O3-AG phosphors transformed from the pure Y2O3 cubic structures, except for SO42− based phosphor materials. The SEM micrographs showed that the particles were formed in the micrometer range with different sizes and shapes. The FTIR spectra revealed the presence of various structural groups in the Y2O3, Y2O3-AG: Eu3+ phosphors. Moreover, the optical diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) properties were investigated. Using the DRS data, the optical band gap energy values were obtained from the Kubelka-Munk function theory. Upon 395 nm excitation, the Y2O3-AG: Eu3+ phosphors emitted red light at 615 nm wavelength. Among all the samples, the Y2O3-BO3: Eu3+ produced the highest intensity of red-light emission. The International Commission on Illumination color coordinates indicated that these phosphors are potential candidates for producing enhanced red color components in white light-emitting diode (W-LEDs) applications.

Realization of Broadband Near-Infrared Emission with High Thermal Stability in YGa3(BO3)4: Cr3+ Borate Phosphor.

As a key material for phosphor-converted light-emitting diodes (pc-LEDs) applications, broadband near-infrared (NIR) phosphors currently face poor thermal stability issues. In this work, we synthesized a broadband near-infrared phosphor YGa3(BO3)4: Cr3+ (YGBO: Cr3+) with a high thermal stability. The YGBO: Cr3+ sample exhibits a broadband near-infrared emission centered at 770 nm with a full width at half-maximum (fwhm) of 2130 cm-1 under blue light excitation. Benefiting from the borate host crystal's strong structural rigidity, wide optical band gap, and weak electron-phonon coupling strength, YGBO: Cr3+ demonstrates strong luminescence thermal stability, and the corresponding luminescence intensity can maintain 80% at 150 °C compared to room temperature. Furthermore, we fabricated a pc-LED device using a blue light chip and YGBO: Cr3+ phosphor, and confirmed its application potential as a near-infrared light source in the spectral analysis of fruit freshness.

Highly Monochromatic Ultraviolet LED Based on the SnO2 Microwire Heterojunction Beyond Dipole-Forbidden Band-Gap Transition.

SnO2 has been extensively applied in the fields of optoelectronic devices because of its large band gap, high exciton binding energy, and outstanding optical/electrical properties. However, its applications in ultraviolet light-emitting diodes (LEDs) are still hindered by the dipole-forbidden rule. Herein, the dipole-forbidden rule can be conquered by synthesizing Sb-incorporated SnO2 microwires (SnO2:Sb MWs), which are examined by ultraviolet photoluminescence emitting at 363.2 nm and a line width of 11.3 nm. Subsequently, a highly monochromatic ultraviolet light-emitting diode (LED) based on a SnO2:Sb MW heterojunction was constructed with a p-GaN film serving as the hole supplier. In the LED, the presence of a MgO intermediate layer can modulate carrier transport and recombination path, thus achieving band-edge optical transition in the SnO2:Sb MW. As the LED is modified using Ag nanowires, electrical properties, especially for the hole injection efficiency, were dramatically boosted, contributing significantly to the device high brightness. The LED emits at 365.9 nm and a line width of 12.4 nm. Therefore, we have realized a high-brightness and narrow-band ultraviolet LED with the shortest peak wavelength never seen in previously reported SnO2 LEDs. This work will promote the potential applications of low-dimensional SnO2 optoelectronic devices and provide an effective exemplification to overcome the dipole-forbidden rule in metal-oxide materials with "forbidden" energy gaps.

Structural diversity and photoluminescence enhancement of indium-based hybrid metal halides

Low-dimensional organic-inorganic metal halides have attracted increasing attention for their diverse structure and excellent photoelectric properties. Here, we report two zero-dimensional indium-based halides, (C3H12N2)3In2Cl12·2 H2O ([C3H12N2]2+ is N-methylethylenediamine cation) with space group of P-1 and (C3H12N2)2InCl7 with space group of P21/c. Upon UV excitation, 1 %Sb doped (C3H12N2)3In2Cl12·2 H2O exhibits luminescence centering at 588 nm with a full width at half-maximum of 149 nm (0.527 eV), as well as a large Stokes shift of 262 nm (1.69 eV) with photoluminescence quantum yields as high as 56 %. The broad emission originates from the electron transitions of the Sb3+ 5s2 lone pair. 1 %Sb doped (C3H12N2)3In2Cl12·2 H2O exhibits more intense, broader emission and larger Stokes shift than that of 1 %Sb doped (C3H12N2)2InCl7 which is due to that the crystalline water increases the hydrogen bonding and leading to more distorted [SbCl6]3- octahedra. This work unveiled the relationship between structure and photoluminescence properties, and provide new types of organic-inorganic metal halides for potential application in light-emitting diodes.

Versatile properties of BaGd2ZnO5:Ho3+ nanomaterial: Compatible towards solid state lightening, anti-counterfeiting and biomedical applications

For the first time, BaGd2ZnO5:Ho3+ (1–11 mol %) nanophosphor (BGZO:Ho3+ NPs) is prepared using combustion synthesis by utilizing glycine as fuel. Phase purity is evaluated using Rietveld refinement and X-ray diffraction. Through crystallographic analysis, the orthorhombic symmetry type with Pbnm (62) space group has been determined. The size of the non-uniformly aggregated particles examined by morphological analysis ranges from 37 to 53 nm. Asignificant photoluminescence (PL) emission observed at 551 nm (green colour) for the 5S2+5F4→5I8 transition. Due to non-radiative energy transfer via cross-relaxation, concentration quenching is observed beyond 9 mol %. Thechromaticity coordinates of BGZO:9Ho3+ NPs is(x = 0.2870, y = 0.7016) suggested that it would be suitable for green emission in white light emitting diode applications. In this case, a flexible light-emitting polydimethylsiloxane (PDMS) material serves as the framework for an anti-counterfeiting (AC) technique. Thrombosis is considered as a major threat to the society as it leads to death and disability. Despite, several risk factors oxidative stress has been considered as the key contributor of thrombosis. The most promising NPs were subsequently investigated for their ability to reduce oxidative stress and thrombosis. It is perceived that NPs demonstrated antioxidant properties by scavenging DPPH (2, 2-diphenyl-1-picrylhydrazyl). In addition, the phosphor inhibited platelet aggregation induced by Adenosine di-phosphate (ADP). The overall results clearly indicated that BGZO:Ho3+ NPs opens up a new avenue in forensic applications.

Structural and luminescence performance of the Eu3+ doped alkaline combined metal oxide-based sodium phosphate phosphors; NaMPO4 (M = Mg, Ba, and Ca) for LED applications

The present research module is about the synthesis of Eu3+ ions-doped NaMPO4(M = Mg, Ba, and Ca) phosphate phosphors by the solution combustion synthesis method. The phase formation and chemical structures of alkaline combined metal oxide-based sodium phosphate phosphors are characterised by X-ray powder diffraction (XRD) and FT-IR measurements. Optimized crystal geometries were generated by employing VESTA software. The crystallite size was calculated from the full width at half maximum (FWHM) of the diffraction peak using the Scherrer formula. G-Fourier transformation software (G-FT) was adopted for generating electron density mapping of NaMgPO4 phosphors, 2D mapping, and 3D chicken plots showing crystal sites occupied by the compound’s constituent elements. The particle size distribution was confirmed by XRD diffraction, and SEM analysis found approximately 12 μm. UV–visible and photoluminescence spectroscopy uncover the optical traits of the prepared phosphor. Photo-emissions of Eu3+doped alkaline combined metal oxide-based sodium phosphate phosphors were monitored at possible excitation wavelengths. The orange-red peak observed at 592 nm and 598 nm occurs due to 5D0-7F1 electric dipole transitions. The peak observed at 618 nm corresponds to the forbidden f-f transitions 5D0-7F2. It is worth mentioning that absorption bands originating from the corresponding 5D0-7F2 transition widen the band region; hence, the stark effect becomes complicated. A low-intensity peak of 688 nm was observed in the NaCaPO4 phosphors, attributed to the 5D0-7F3 transition. Chromaticity coordinates and energy level transitions may determine the colour emission materials. The CIE coordinates of NaMPO4:Eu3+phosphors exhibit reddish emission and find application in light-emitting diodes (LEDs) and illuminating displays.

Cascading Energy Transfer for Highly Efficient Deep-Red OLED Emission with Cyclometalated [3+2+1] Iridium Complexes.

The promising cyclometalated iridium (III) complexes have been proved to possess great potential in vacuum-deposited organic light-emitting diodes (OLEDs) applications for full-color displays and white solid-state lighting sources. Herein, based on the unique bidentate ligand of dibenzo[a,c]phenazine (dbpz) group with strong conjugated effect of aromatic rings for red emission, four novel [3+2+1] coordinated iridium (III) emissive materials have been rationally designed and synthesized. The monodentate ligands of -CN and -OCN have been effectively employed to tune the deep-red emission of 628-675nm with high photoluminescence quantum yields up to 98%. Moreover, all devices displayed deep-red color coordinates ranging from (0.675, 0.325) to (0.716, 0.284), which is close to the standard-red color coordinates of (0.708, 0.292), as recommended by International Telecommunication Union Radiocommunication (ITU-R) BT.2020. The device based on nBuIr(dbpz)CN with an exciplex cohost has exhibited maximum external quantum efficiencies of 20.7% and good stability. With nBuIr(dbpz)CN as an effective sensitizer, the nBuIr(dbpz)OCN based phosphorescent OLED devices have successfully demonstrated cascading energy transfer processes, contributing to pure red emission with maximum luminance as high as 6471cd m-2. Therefore, this work has been successfully demonstrated rational molecular design strategy of [3+2+1] iridium complexes to obtain highly efficient deep-red electrophosphorescent emission.

Facile synthesis of anthracene-based derivatives via a magnetically retrievable Fe3O4@SiO2 immobilized selenoether functionalised NHC-Pd(II) heterogenous catalyst: Photophysical, electrochemical and DFT studies of novel 9,10-anthracene based derivatives

A series of anthracene-based derivatives, which are promising candidates for Organic light-emitting diode (OLEDs) applications, have been synthesized through the Suzuki Miyuara cross-coupling reaction of dibromo anthracene and phenylboronic acids derivatives. A magnetically separable heterogeneous catalyst Fe3O4@SiO2@NHC^SePh-Pd(II) was used, and the coupling reaction was investigated under aerobic conditions using water as a green solvent. A very mild approach for the arylation of the 9,10-dibromo anthracene molecules was adopted to harvest a series of highly conjugated anthracene derivatives. The catalyst was reused for up to seven catalytic cycles without much loss in catalytic efficiency. The 55% transformation in the seventh catalytic cycle indicates the catalyst's robustness and high catalytic potential. Necessary photophysical studies were conducted for selected synthesized anthracene-based derivatives, which includes the absorption, emission and cyclic voltammetric studies. Moreover, the thermogravimetric analysis (TGA) was also conducted to check the thermal stability of the compounds. Finally, a Density Functional Theory (DFT) study was conducted, and it revealed that comparing two anthracene derivatives, the Highest occupied molecular orbital (HOMO) and Least unoccupied molecular orbital (LUMO) energy levels, as well as the HOMO-LUMO gap (HLG), differ, with 9-([1,1′-biphenyl]-4-yl)-10-(4-fluorophenyl) anthracene exhibiting a relatively large HLG. The HOMO is localised along the molecule's main axis, while the LUMO is more delocalised on atoms.

Non-concentration quenching phosphor Na2YbMg2(VO4)3: Eu3+ for WLEDs and optical thermometry applications

Red-emitting phosphors with high efficiency and good thermal stability is of great importance for white light-emitting diodes (WLEDs) application. Here, Eu3+ doped Na2YbMg2(VO4)3 red-emitting phosphors were successfully prepared by the sol-gel method. The crystal structures, luminescence properties, and thermal stability of the samples were investigated and discussed in detail. Surprisingly, no concentration quenching effect was observed even though the doping concentration of luminescent centers reach 100 %. The intense red emission under 355 nm excitation, high color purity (95.34 %), high quantum yield (75.2 %), and a high value of activation energy (0.293 eV) indicate that the phosphors have promising applications for WLEDs. Finally, the samples were prepared as red-light components for WLEDs. The correlated color temperature, and color rendering index of the WLEDs devices driven by 400 mA current were 4902 K, and 78.1, respectively. The temperature sensing properties based on the fluorescence intensity ratio (FIR) technique was discussed. The maximal absolute sensitivity of the sample is up to 5.08 % K−1 at 480 K. Hence, the as-prepared sample has potential applications in the lighting field and optical thermometry.

Mechanoluminescence and photoluminescence properties of Eu3+ -activated SrGa2 O4 phosphors.

Red-emitting Eu3+ activated SrGa2 O4 phosphors were synthesized using a conventional solid-state reaction method. The structural, optical, and luminescence properties were systematically investigated. The synthesized phosphors are single phase with a monoclinic structure. There are no significant changes in the phase and the crystal structure of the host matrix after incorporating Eu3+ ions. The undoped and Eu3+ doped SrGa2 O4 phosphors exhibited good mechanoluminescence (ML) emission without any irradiation with ultraviolet (UV) or gamma rays. Eu3+ -activated SrGa2 O4 phosphors have prominent red emission attributed to 5 D0 → 7 F2 forced electric dipole transition excited at 395 nm. The colour coordinates and purity of the SrGa2 O4 : 0.08 Eu3+ phosphor were calculated to be (0.6102, 0.3810) and 97.6%, respectively. The quantum efficiency is 12.68%, and was better than that of commercially available red phosphors. The ML and photoluminescence studies revealed that the synthesized phosphors can act as potential candidates for stress sensors, UV or near-UV light-emitting diodes (NUV LEDs) and components of phosphor-converted white light-emitting diode (pc-WLED) applications.

Synthesis, structural and optical properties of a novel double perovskite for LED applications

Amidst growing concerns for environmental sustainability and green ecology, the utilization of Light Emitting Diodes (LEDs) for indoor plant cultivation has emerged as an influential area of research. Nonetheless, the growth of indoor plants is often constrained by inadequate lighting. Consequently, designing novel LEDs to create an appropriate light environment has emerged as a focal point in research. As a new type of photocatalytic material with excellent optical properties and light stability, double perovskite has broad application prospects in LEDs manufacturing. In this context, this article aims to synthesize a new Ca2Lu(Nb,Mn)O6 double perovskite and study its optical properties in LEDs lighting for indoor plant growth. A new Ca2Lu(Nb,Mn)O6 double perovskite were synthesized using the traditional high-temperature solid-phase method. The crystal structure and luminescence properties of the double perovskite were characterized in detail using powder X-ray diffraction (XRD), Rietveld refinement, excitation and emission spectra, decay lifetimes, quantum efficiency (QE), electron paramagnetic resonance (EPR) spectra, temperature-dependent emission spectra, and the Commission International de l’Eclairage (CIE) color coordinates. The photoelectric properties of Ca2Lu(Nb,Mn)O6 and Ca2LuNbO6 double perovskite have been explored through first-principles investigations. The absorption spectra from 270 to 600 nm indicates that it can be effectively excited by ultraviolet (UV) light. The emission spectra show a strong broad red emission peak at 684 nm. The luminescence mechanism has been studied using the Tanabe-Sugano diagram. In addition, the internal UV emission ratio β1, crystal field strength Dq, and Racah parameters B and C were evaluated. The thermal stability of the sample was studied through emission spectra at heating temperatures from 303 to 573 K. The results indicate that Ca2Lu(Nb,Mn)O6 double perovskite provides a new solution for indoor plant growth.

Luminescence properties of ZrO2: Dy3+ phosphor for solid-state lighting applications

Herein, we report Dy3+-activated ZrO2 phosphors synthesized via the sol-gel technique. The structural, morphological, and optical properties of the synthesized powder samples annealed at 900 °C were investigated. The monoclinic phase of the synthesized phosphor was confirmed by recording the X-ray powder diffraction (XRPD) pattern. Ultraviolet–visible analysis was performed for the reflectance and bandgap measurements of the phosphors. Field emission scanning electron microscope and X-ray energy dispersive spectroscopy analyses were used to study the morphology and elemental composition of the phosphors, respectively. The distribution of ions in the undoped and Dy3+-doped samples was confirmed using time-of-flight secondary ion mass spectroscopy. The photoluminescence (PL) behavior of the synthesized phosphors was investigated by recording the excitation and emission spectra. When the synthesized phosphors were exposed to UV light at 353 nm, we observed characteristic blue and yellow Dy3+ PL emissions, corresponding to the transition 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2, respectively. Additionally, we observed low-intensity red and brown-red emission peaks corresponding to 4F9/2 → 6H11/2 and 4F9/2 → 6H9/2. These observations indicate that the non-aqueous sol-gel route, coupled with the suitable post-synthesis heat treatment, resulted in the development of a monophase (monoclinic) zirconia. This makes it a strong candidate for phosphor applications due to its high room temperature stability and efficient characteristic features of the monoclinic phase. These findings strongly suggest that Dy3+-doped ZrO2 can serve as a superior phosphor material for white light-emitting diode applications.

Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.

Achieving nearly zero-thermal quenching luminescence of tellurate phosphor via substitution of alkaline earth metal

The luminescent thermostability of phosphor is a crucial factor for white light-emitting diode (w-LED) application. To improve the luminescent thermostability, the diverse modulation strategies were proposed. In this study, it was shown that cationic substitution can greatly enhance the luminescence thermostability in the Dy3+-activated BaLaLiTeO6 double perovskite phosphor. With the substitution of alkaline earth metal cations (Sr2+, Ca2+ and Mg2+) for Ba2+, the variations of the Dy3+ local symmetry and structural rigidity contribute to the improved emission intensity and thermostability, respectively. In particular, the MgLaLiTeO6:Dy3+ (MLLT:Dy3+) phosphor exhibits exceptional thermostability. When the temperature was increased up to 473 K, the luminescence intensity only loses 4.1 % of the initial level, and it is known as nearly zero-thermal quenching. Moreover, a w-LED device was assembled with the MLLT:Dy3+ phosphor as yellow component. The satisfactory electroluminescence performance was obtained. The results revealed that the phosphor is of great potential for the w-LED applications.