Blue Emission Band Research Articles

Gd(III)/Dy(III)-based coordination polymers for luminescent and magnetic properties

Two isostructural lanthanide-based coordination polymers, namely, {[Gd2(H2dhtp)3(DMF)2(H2O)4]·2DMF·H2On (1) and {[Dy2(H2dhtp)3(DMF)2(H2O)4]·2DMF·H2O}n (2) (H4dhtp = 2,5-dihydroxyterephthalic acid, DMF = N, N-dimethylformamide) were synthesized and structurally characterized by single-crystal X-ray diffraction, IR, powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and elemental analysis. Compounds 1 and 2 exhibited 3D networks and isostructures, except for the distinction of the metal ion. Magnetic measurements indicated that complex 1 exhibited the dominating contribution at low temperature of zero-field splitting for Gd(III) materials, and the complex 2 shown the depopulation of the excited excited state for Dy(III) material. The solid luminescent properties of H4dhtp, 1, and 2 displayed a blue emission band, while the solution state luminescent properties all demonstrated a green emission band. The combination of luminescence sensing and magnetism in single-phase coordination polymers may offer great potential applications in smart multitasking devices.

Study of the lighting characteristics of Uniel retrofit LED lamps

The paper considers the photometric characteristics of LED retrofit lamps produced by the Russian-Chinese company Uniel: Uniel LED-G45-6W/4000K, Uniel LED-A60-8W/6500K, and Uniel LED-A60-9W/4000K, designed to replace traditional incandescent bulbs. During the research, comprehensive measurements of photometric parameters (luminous flux, power consumption, color temperature, color rendering index, ripple factor, power factor) have been carried out and the luminous efficacy has been calculated. The results of the measurements have been presented in relation to the supply voltage. Based on the data obtained, an analysis is carried out of the compliance of the initial measured characteristics of the lamps with the values declared by the manufacturer. The analysis of the emission spectra leads to the conclusion that the Uniel LED-A60-8W/6500K lamps are equipped with white light-emitting diodes, the spectrum of which consists of a blue emission band from the semiconductor crystal with a maximum at ~450 nm and a phosphor band with a maximum at ~560 nm, which converts some of the blue emission from the crystal into long-wavelength spectrum. The emission spectra of the Uniel LED-G45-6W/4000K and Uniel LED-A60-9W/4000K lamps, in addition to the blue emission band from the semiconductor crystal with a maximum at ~450 nm, contain emissions from two phosphors, the bands of which have maxima at ~560 nm (green) and ~630 nm (red), which results in a lower color temperature of the LEDs. The paper also provides a detailed analysis of the light power distribution curves, thermal operating conditions, and structural features of the lamps. The research results lead to the conclusion that it is advisable to recommend Uniel LED-G45-6W/4000K and Uniel LED-A60-9W/4000K lamps for use as light sources to replace traditional incandescent lamps because their photometric characteristics comply with the declared parameters and permissible deviations specified in the regulatory standards.

Manganese and iron-doped yttrium borate as an excellent multifunctional inorganic material

Manganese and iron-doped π-YBO3 have been synthesized using a modified epoxide-mediated gel method. The PXRD pattern evaluated the formation of the desired phase and the structural changes. EDS spectra determined the elemental analysis of undoped and doped samples. Raman spectra observed the stretching and bending modes of B-O bonds. The direct band gaps for doped samples were 1.47 and 2.07 eV, respectively, lower than the band gap value of 5.81 eV for π-YBO3. The green and blue indigo emission bands were observed in the photoluminescence spectra. Doped samples showed good magnetic properties as they are antiferromagnetic and ferromagnetic at low temperature (T = 5 K) M-H plot and SQUID measurement. An indigenously built Sawyer-Tower circuit is used to measure ferroelectric hysteresis. Photodegradation studies of RhB were conducted under UV-visible irradiation.

Study of blue-light emission properties of WO3:Eu microstructures

Structural, surface morphological, optical absorption and emission properties of 0–5% Eu doped WO3 samples are studied. The samples are synthesised by acidic precipitation method. The structural analysis reveals that the sample has ‘room-temperature monoclinic’ structure. The average crystallite size of the undoped sample is ∼58.57 nm and it decreases to 34.72 nm after doping of Eu at 5%. The undoped sample has hexagonal disc-like grain structures with average diameter of ∼0.84 μm. All the samples show a sharp absorption edge above 350 nm. The transmittance of the samples increases above 400 nm and reaches its maximum at ∼490 nm. The extinction coefficient of the undoped sample is minimum at 390 nm and it has a relatively smaller value than that of the doped samples. The optical bandgap of the undoped sample is found to be 3.56 eV and it decreases to 3.28 eV with the increase of concentration of Eu to 5%. Analyses of PL spectra show that the undoped sample under 355 nm UV excitation produces a broad blue emission band with five maxima at ∼403, 414, 435, 473 and 495 nm due to band-to-band transitions and transitions involving intrinsic defects. A blue emission band centred at ∼435 nm is increased by two-fold after doping of Eu at 1%. In addition, a secondary emission band is found at ∼505 nm due to formation of an aggregate defect (F2 centre). When the doping concentration is increased to 5%, another secondary band is observed at 610 nm due to interstitial Eu3+ centre. The enhancement of the blue emission band is attributed to formation of oxygen vacancies due to substitution of W6+ ions by Eu3+ ions. The enhanced blue light in the sample doped with 1% of Eu has potential application in WLED as well as other light emitting applications.

Full-visible-spectrum LED lighting by using a near-UV-excitable broadband blue-emitting Ca2LuHf2GaAl2O12:Ce3+ garnet phosphor

Highly efficient broadband blue-emitting phosphors are urgently needed for full-visible-spectrum white light-emitting diodes (WLEDs). Herein, we report a new highly luminescent garnet-type Ca2LuHf2GaAl2O12:Ce3+ (abbreviated as: CLHGAO:Ce3+) blue phosphor enabling full-visible-spectrum LED lighting. These CLHGAO:Ce3+ phosphors doped with different Ce3+ concentrations have been prepared by using a high-temperature solid-state reaction approach, and their phase purity, crystal structure, luminescent properties, CIE color coordinates, and quantum efficiency have been systematically studied. Importantly, CLHGAO:Ce3+ blue phosphors show a broadband excitation spectrum in the 300–450 nm spectral range peaking around 398 nm, matching well with the emission wavelengths of commercial near-ultraviolet LED chips (380–420 nm). Upon 398 nm excitation, the optimal CLHGAO:2%Ce3+ phosphor sample generates a bright broad blue emission band (emission peak: 472 nm; bandwidth: 84 nm) with high internal quantum efficiency of 79.2% and external quantum efficiency of 55.3%. Notably, the emission intensity of CLHGAO:2%Ce3+ phosphor is about 1.87 times higher compared to the commercial BaMgAl10O17:Eu2+ blue phosphor (emission peak: 451 nm; bandwidth: 53 nm). Finally, a white LED device is fabricated with a 395 nm near-UV LED chip with CLHGAO:2%Ce3+ blue phosphor and commercial (Ba,Sr)2SiO4:Eu2+ green phosphor as well as commercial CaAlSiN3:Eu2+ red phosphor, and the device demonstrates bright warm-white emission with an ultrahigh color rendering index (Ra = 95.1, R9 = 97.8, R12 = 88.4) and low correlated color temperature of 3540 K. These results show that as-developed blue-emitting CLHGAO:Ce3+ garnet phosphors with superior photoluminescence properties can potentially be used in phosphor-converted full-visible-spectrum WLEDs.

Temperature-Dependent Color-Tunable Afterglow in Zirconium-Doped CsCdCl3 Perovskite for Advanced Anti-Counterfeiting and Thermal Distribution Detection.

Persistent luminescence (PersL) materials exhibit thermal-favored optical behavior, enabling their unique applications in security night vision signage, in vivo bioimaging, and optical anti-counterfeiting. Therefore, developing efficient and color-tunable PersL materials is significantly crucial in promoting advanced practical use. In this study, hexagonal Zr4+ -doped CsCdCl3 perovskite is synthesized via a hydrothermal reaction with a tunable photoluminescent (PL) behavior through heterovalent substitution. Moreover, the incorporation of Zr4+ ions result in an extra blue emission band, originating from the enhanced excitonic recombination in D3d octahedrons. Furthermore, the afterglow performances of the samples are dramatically improved, along with the noticeable temperature-dependent PersL as well as the thermo-luminescence with tunable color output. Detailed analysis reveals that the unique temperature-dependent PersL and thermo-luminescence color change are attributed to the presence of multiple luminous centers and abundant traps. Overall, this work facilitates the development of optical intelligence platforms and novel thermal distribution probes with the as-developed halides perovskite for its superior explored PersL characteristic.

Electrochemical exfoliation of phosphorus doped carbon dots with dual-emission originating from carbon core and surface states

Carbon dots have attracted significant attention due to their versatile and excellent photoelectric properties; however, the origins and underlying mechanism remain a subject of debate especially for dual-emission CDs. Here, novel dual-emission CDs have been exfoliated from graphite rods via an electrochemical method in a dihydrogen phosphate electrolyte. The CDs possess a very narrow blue emission band in the short wavelength region and a broad cyan emission band in the long wavelength range, which are attributed to carbon core state and surface state from phosphorus atom doping, respectively. Interestingly, the former shows excitation-dependent behavior, but the latter is excitation-independent. Thus, as the excitation wavelength increases, the blue emission band is gradually closing to the cyan one and coalesce into a broad peak at the excitation wavelength of 420 nm. The variations of both emission intuitively illustrate the role transition between a core state and the doped surface state at different excitation wavelengths, which offer a real sample for the study of transition between emissive states. Our findings provide novel and fundamental insights on the fluorescence mechanism of CDs with dual-emission.

Understanding the effect of Mn2+ on Yb3+/Er3+ co-doped NaYF4 upconversion and obtaining the optimal combination of these tridoping

In this work, we investigated in detail the upconversion properties of several types of nanoparticles, including NaYF4:5%Yb3+/30%Mn2+, NaYF4:40%Mn2+/x%Yb3+ (x% = 1, 5, 10, 20, 30, and 40), NaYF4:2%Er3+/x%Mn2+ (x% = 20, 30, 40, 50, 60, and 70), NaYF4:40%Mn2+/x%Er3+ (x% = 1, 2, 5, and 10), and NaYF4:40%Mn2+/1%Yb3+/x%Er3+ (x% = 0, 2, 5, and 10). We studied their upconversion emission under 980 nm excitation in both pulsed and continuous wave modes at different synthesis temperatures. The nanoparticles were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), and photoluminescence (PL) spectroscopy. The doping of Yb3+ and Mn2+ ions resulted in the nanoparticles assuming cubic and hexagonal crystal structures. The emission intensity increased (106.4 (a.u.*103) to 334.4(a.u.*103)) with increasing synthesis temperature from 120 to 140 °C, while a sharp decrease was observed when the synthesis temperature was increased to 200 °C. The gradual decrease in peak intensity with increasing Mn2+ concentration from 20 to 70% was attributed to energy transfer from Mn2+ to Yb3+. In NaYF4:Mn2+/Yb3+/Er3+ UCNPs, increasing the Er3+ concentration from 0 to 10% led to the disappearance of the blue, orange, and green emission bands. The intense upconversion luminescence pattern with high spatial resolution indicates excellent potential for applications in displays, biological sensors, photodetectors, and solar energy converters.

A Study on the Inclusion of Higher Dopant Proportion on ZrO<sub>2 </sub>Thin Film Deposited by Spray Pyrolysis Method

In this present work, Pristine and 10 at.% of In-doped ZrO2thin films were deposited by spray pyrolysis technique at optimized substrate temperature [Ts=450°C]. The greater the proportion of Indium ion dopant, significantly influences the structural, optical, morphological, and electrical properties of deposit thin films. The deposited thin films were characterized with XRD, UV-Vis, PL, HR-TEM with EDAX, and I-V characterization Studies. The crystallinity of Zirconium dioxide thin film was improved and size of crystals were decreased by Indium ion substitution. Optical study revealed that the film's optical transmittance enhanced from 80.3 percent to 86.5% as a result of the dopant. The energy bandgap increased at 4.93eV - 4.57eV, systematically. HR-TEM studies show the homogeneous particle distribution and denser surface texture at 22nm and 19nm of average particle agglomerations. The study of PL emission shows an increase in intensity on the blue emission band with enriched crystalline quality. The conductivity of the ZrO2 was higher affected by Indium ion may result in increased conductivity, with low resistivity property.

Mechanistic Insight into the Defect-Engineered White Light Emission from the Single-Phase Orthovanadate Phosphor Synthesized by a Facile Rapid Microwave-Assisted Synthesis.

The synthesis of single-phase barium orthovanadate phosphors by a one-pot microwave-assisted hydrothermal approach has been reported, wherein the homogeneous thermal zone generated at the molecular level by microwave radiation gives rise to tunable distortion in the tetrahedral VO4-3 and oxygen vacancies, eventually enabling intrinsic white light emission with CIE of 0.31,0.38, high photoluminescence internal quantum efficiency of 35%, and external quantum efficiency of 28% whereas phosphor synthesized by the hydrothermal route exhibits only bluish-green emission (PLQE: 0.5%). The Rietveld refinement confirms the formation of a single trigonal phase having dissimilar V-O bond lengths and bond angles, implying the formation of a distorted phosphor under optimized conditions, and corroborates with Raman and Fourier transform infrared analyses. The X-ray photoelectron spectroscopy and electron paramagnetic resonance analysis reveal that the origin of white light emission is due to short- and long-range defects, in particular the oxygen vacancies, which eventually form an intermediate energy level in the forbidden region between the valence and conduction bands. Lifetime spectra show triexponential fitting, corresponding to two charge transfer blue and green emission bands (3T2, 3T1 to 1A1) and one oxygen vacancy-related red emission at RT. Furthermore, these phosphors are thermally stable, as no change in the structure or emission characteristics are observed. A prototype fabricated using a 365 nm chip exhibits white-light-emission CIE of 0.353,0.392, correlated color temperature of 4867 K, color rendering index of 85, and high luminous efficacy of 102 lm/W at 140 mA operating current, portentous for practical applications.

Probing analysis of Cu-doping on the structural, optical, morphological and magnetic properties of hematite nanoparticles and their antibacterial activity

The present study describes the synthesis of pure and Cu doped α-Fe2O3nanoparticles (with various concentrations of Copper 1, 3, 6, and 9 wt%) by conventional chemical precipitation technique and examines their structural, morphological, optical, magnetic, and antibacterial capabilities. The XRD pattern of pure and Cu-doped α-Fe2O3 nanoparticles exhibit rhombohedral structure and the estimated crystalline sizes were ranged from 39 to 58 nm. It is discovered that the estimated density dislocations linked to the agglomeration/cluster formations diminish when interstitial vacancies are filled with copper. The obtained bandgap from Tauc’s plot, 2.07 eV of pure α-Fe2O3 is found to less than Cu doped α-Fe2O3 nanoparticles (2.9–3.4 eV), due to the structural changes and the tailing of localised states into deep bandgap energy levels. The intense blue emission bands (410–490 nm) arised due to the movement of trapped electrons from the donor level to the valance band and broad green emission bands (522–560 nm) are due to deep level CuO defect to the Fe2O3. The fundamental stretching of Fe-O vibrations and the presence of Cu in prepared samples were identified in FTIR and Raman spectra. SEM micrograph shows the uniform distribution of spherical nanoparticles with size ranged from 39 to 61 nm, which is in good accord with XRD studies. Further, the magnetic characteristics of the pure and Cu-doped α-Fe2O3 samples were assessed using a vibrating sample magnetometer (VSM); the ensuing hysteresis loop of the Cu-doped α-Fe2O3 displays weaker ferromagnetic behaviour. In the present investigations, the disc diffusion technique has been used to examine the antibacterial activity. Thus, the results of antibacterial activities demonstrated that at concentrations of 200 and 500 μg/ml of pure and Cu-doped α-Fe2O3 NPs, the highest zone of inhibition was found against gram (+ve) positive bacteria and was followed by the gram (–ve) negative bacteria’s.

Tunable emission, energy transfer and cation substitution in the Li2Sr2Al(PO4)3:Dy3+, Eu3+, Na+ phosphor for WLEDs application

The current investigation deals with the synthesis and characterization of the singly, double and triple ions (Dy3+, Eu3+, Na+) co-doped Li2Sr2Al(PO4)3 phosphors. The entire series of suggested phosphors has been successfully synthesized using a straightforward combustion method and their XRD and Rietveld refinement pattern confirms the phase formation and successful synthesis of material. The morphological behaviour, elemental composition, vibrational features, thermal stability and luminescence properties were carried out by SEM-EDAX analysis, FT-IR, TG-DTA and photoluminescence techniques. The single Dy3+ doped Li2Sr2Al(PO4)3 phosphors exhibits blue and yellow emission band around at 482 nm and 572 nm monitored at 350 nm, 365 nm, 388 nm excitation. While, Eu3+ doped Li2Sr2Al(PO4)3 phosphors exhibits orange and red emission band around at 592 nm and 615 nm under 395 nm and 466 nm excitation. According to Froster and Dexter theory, the PL excitation spectrum Dy3+ doped Li2Sr2Al(PO4)3 phosphor and Eu3+ doped Li2Sr2Al(PO4)3 phosphor are overlapped to each other. Consequently, an investigation was conducted to study the transfer of energy between Dy3+ and Eu3+. In addition, to improvement in emission intensity and color tunning host cation (Li+) replaced with another cation (Na+) and their impact was studied. The photometric characterization like CRI Chromaticity coordinate, CRI and CCT values are also estimated using color calculator. The host cation substitution revealed that performance of Dy3+/Eu3+ doped Li2Sr2Al(PO4)3 phosphors were improved with doping of Na+ ions. The overall study and their estimated results suggested that Dy3+, Eu3+, Na+ ions doped Li2Sr2Al(PO4)3 phosphors have huge ability for WLEDs application and their future investigation.

ZnO nanocomposites containing Cd are synthesized with high photodegradation potential for wastewater treatment

The zinc oxide (ZnO) nanoparticle on a two - electron oxygen reduction reaction is a particularly promising candidate for in-situ application. Herein, we prepared the Cd doped ZnO nanocomposites through a simple hydrothermal method. The X-ray diffraction (XRD) analysis has been carried out to confirm the structure and size of the nanomaterial. The optical absorption and energy gap of the prepared nanoparticles have been identified by UV–vis-NIR studies. Photoluminescence (PL) studies on the synthesized nanomaterials confirm the characteristic existence of blue and green emission bands. Fourier transform infrared (FTIR) spectroscopy has been studied on the ZnO nanoparticles to analyze the -OH and CO-O vibrations. The structural and surface morphology analysis was inferred by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) microanalysis. Cd doped ZnO nanocomposites are environmentally friendly and can be utilized to quickly remove contaminants from wastewater. The findings from the adsorption equilibrium fit the Brunauer-Emmett-Teller (BET) model very well, showing multi-layer adsorption. The photodegradation studies on Cd doped ZnO nanocomposites were carried out, which is an advanced oxidation process widely used for methylene blue removal. Therefore, the higher photocatalytic performance revealed that Cd doped ZnO nanocomposites could be a promising photocatalyst for environmental remediation applications.

Impact of varying Li+ concentration on the upconversion emission and temperature sensing characteristics of YVO4: Tm3+/Yb3+ phosphor

A series of Li+ codoped YVO4: Tm3+/Yb3+ phosphors were prepared by Pechini sol–gel reaction technique. Structural study of the material confirms the crystal structure of the prepared samples and also gives information about the crystallite size and phase purity with the variation of Li+ ion concentrations. Emission peaks around ∼ 476, and ∼ 799 nm corresponds to the 1G4→3H6, and 3H4→3H6 transitions, which could be seen under irradiation of NIR (980 nm) laser light. Li+ (10 mol%) codoped sample shows maximum upconversion. Li+ doping significantly increases the up-conversion emission intensities by more than 5 times for emission peaks around 476 nm and 799 nm.The possible explanation for the increase in UC (Upconversion) emission intensity is attributed to both improved crystallinity and crystal field modification around Tm3+ ions. The variation of UC emission spectra with respect to pump power was observed to investigate the underlying UC luminescent mechanism in YVO4: Tm3+/Yb3+ codoped with Li+ (10 mol%). The multiphoton involvement is observed in the power-dependent study of upconverted blue and NIR emission bands. Widely used fluorescence intensity ratio (FIR) technique was used to evaluate the temperature sensing capability of the optimized Li+ codoped phosphor. The FIR study of Stark components 3F2, and 3H4 levels indicates that this material is an efficient material for temperature sensing. The optimized sample, doped with Li+, exhibits relative sensitivity of 0.78% K−1 at a temperature of 548 K. This material have utility in both light-emitting diodes and as a temperature-sensing probe.

Spectroscopic and temperature sensing properties of Sm3+ in self-activated CsLu(WO4)2 phosphors

In this research, a series of Sm3+ doped CsLu(WO4)2 phosphors was prepared via high temperature solid phase technique to design new red phosphors and optical thermometric materials. Their structures, morphology, band gap and luminescence properties were characterized by X-ray diffraction, scanning electron microscopy, diffuse reflection and luminescence spectra, respectively. Under UV excitation, CsLu(WO4)2 gives rise to a blue broad emission band between 350 and 700 nm, which stems from the 3T1u → 1A1g transition of WO66− groups. When Sm3+ is introduced into CsLu(WO4)2, energy transfer between WO66− groups and Sm3+ ions takes place in CsLu(WO4)2:Sm3+ phosphors, and color-tunable luminescence from blue to red is realized by controlling the Sm3+ doping concentration. The energy transfer efficiency between WO66− groups and Sm3+ ions was analyzed, and the energy transfer mechanism was determined to be dipole–dipole interactions. According to the temperature-dependent luminescence spectra, WO66− groups and Sm3+ ions exhibit large discrepancy in thermal quenching rates, and thus the temperature sensing properties of CsLu(WO4)2:Sm3+ in the temperature range of 283–403 K were analyzed. Based on the framework of fluorescence intensity ratio theory, the basic optical thermometry parameters including absolute and relative sensitivity of CsLu(WO4)2:Sm3+ were calculated and the results show that it has great potential for application in optical thermometry.

Blue/NIR-emitting Phosphor Based on Sr2CeO4: Tm3+, Yb3+ Obtained by Combustion Synthesis

In this study, pure Sr2CeO4 (SCO) and codoped Sr2CeO4:Tm3+, Yb3+ (SCO:Tm, Yb) of powder phosphors were synthesized by a combustion technique. The concentration of Tm3+ was fixed at 0.5 mol %, while the Yb3+ doping concentration was varied from 0 to 7.0 mol %. The crystalline structure, morphology and luminescence properties were studied using X-ray diffraction (XRD), scanning electron microscope (SEM) and photoluminescence spectroscopy, respectively. The XRD analysis shows the crystalline orthorhombic phase for all synthesized samples of SCO and SCO: Tm, Yb. The SEM results show that the doped sample with 5.0 mol % Yb3+ has the lowest grain particle size of 1.92 mm. The SCO:Tm, Yb phosphors produce mainly blue and near infrared emission bands centered at 481 nm and 813 nm (under 980 nm, excitation) which corresponds respectively to 1G4→3H6 and 3H4→3H6 transitions of Tm3+. In addition, the international commission on illumination CIE coordinates were calculated for all samples taking the range of 400 – 700 nm obtaining for the 5.0 mol % Tm3+ doped sample the coordinates: (x,y) = (0.0833, 0.1671) which match with pure blue color. Due to the strong blue and near infrared emissions, the SCO:Tm, Yb phosphors could be good candidates for use in biomarkers or lighting applications.

High-Efficiency Ce3+ Activated Orthorhombic Lanthanide Silicate Blue Phosphors for Plant Growth Lighting.

Plant growth can be controlled and freed from natural environmental interference through indoor plant cultivation. Artificial light sources with better quality are required to promote indoor plant growth. In this study, we used a simple high-temperature solid-state reaction to synthesize high-efficiency Ce3+-activated NaGdSiO4 (NGSO) phosphors. X-ray diffraction and Rietveld refinement were performed to determine the detailed crystal structure of the NGSO:Ce3+ phosphors. The morphology of NGSO:Ce3+ and the elemental state of Ce3+ were measured and analyzed. Under near-ultraviolet (n-UV) light excitation, the Ce3+-activated NGSO phosphors exhibit a broad emission band from 375 to 500 nm, and their emission peaks are at approximately 401 nm. This asymmetrical blue emission band is caused by the spin-allowed 5d → 4f transition of Ce3+ and overlaps well with the blue absorption region of carotenoids and chlorophyll. The temperature-dependent luminescence spectra were utilized to assess the thermal stability of NGSO:Ce3+. The external quantum efficiency (EQE) was measured to be 60.91%, and the internal quantum efficiency (IQE) was measured to be 73.39%. A blue LED device assembled from the NGSO:Ce3+ phosphor has demonstrated the application potential in accelerating plant growth.

Structural, optical, and dielectric characteristics of pulsed laser deposited SnO2-TiO2 composite thin films

Pulsed laser deposition was used to fabricate the thin films of SnO2 and SnO2-TiO2 composites on FTO substrates and these films were characterized to understand the effect of TiO2 on the structural, optical, and electrical properties of SnO2. The Tauc plots confirm that the composite films have a higher band gap energy than SnO2. EDX spectra demonstrate that the thin films contain Ti, Sn, and O ions. The photoluminescence (PL) spectra indicate three blue emission bands at wavelengths of 410, 435, and 460 nm and these are due to the oxygen vacancies or interstitial oxygen ions and defect-related states. These films are n-type semiconductors as verified by the Hall Effect measurements. At the interface of the film, the frequency dependence of the dielectric at room temperature reveals that as the frequency increases, the dielectric constant and dielectric losses decrease. SnO2 film has a significantly higher a.c. conductivity than the SnO2-TiO2 composite films. The correlated barrier hopping (CBH) mechanism is responsible for the conduction behaviour and obeys Johncher’s power law (n < 1). The addition of TiO2 in SnO2 affects the structural, optical, dielectric, and ac conductivity of films at room temperature.

Trap engineering in ZnGa2O4:Tb3+ through Bi3+ doping for multi-modal luminescence and advanced anti-counterfeiting strategy

Optical information encryption based on luminescence materials have received much attention recently. However, the single luminescence mode of the luminescence materials greatly limits its anti-counterfeiting application with high safety level. Here, a series of luminescence materials of Tb3+ and Bi3+ co-doped ZnGa2O4 phosphors with great correspondence in photoluminescence (PL), persistent luminescence (PersL), and thermoluminescence (TL) modes was synthesized by the conventional solid-phase method for the application in multi-modal anti-counterfeiting fields. Under the excitation of 254 nm, ZnGa1.99O4:0.01 Tb3+, yBi3+ (y = 0.001,0.002) sample exhibited a broad blue emission band (the transition from [GaO6]) at 440 nm and the characteristic emission peaks of Tb3+ at 495 nm, 550 nm, 591 nm and 625 nm, corresponding to the transitions of 5D4-7Fn (n = 6, 5, 4, 3), respectively. Interestingly, the co-doping of Bi3+ ions improve the crystallinity and particle size of the phosphor, subsequently enhanced the PL intensity of Tb3+ to 6 times that of Tb3+ singly doped ZnGa2O4 phosphor. Further, the flexible films with multi-modal luminescence properties have been fabricated through the unique TL and PersL characteristics of ZnGa2O4: Tb3+, Bi3+ phosphors, including “Optical information storage film”, “snowflake and characters” and “QR code”. Moreover, a set of optical information encryption is obtained by combining ZnGa2O4:Tb3+, Bi3+ phosphor and red emitting phosphor. The results indicate that ZnGa2O4:Tb3+, Bi3+ phosphor with multi-modal stimulus response can be expected to be potentially used in the applications of optical information storage and anti-counterfeiting fields.

1,2,4-Triazole-Ligand-based Iridium(III) complex and its use in blue phosphorescent organic light-emitting diodes

Organic light-emitting diodes (OLEDs) play a key role in modern flexible displays. Although stable and efficient red- and green-emitting phosphors have been developed, the applications of blue emitters are limited due to their poor chemical and electrochemical stability, and thus, they require further development. Herein, we report the preparation and full characterization of IrTrz, a 3-methyl-5-phenyl-1H-1,2,4-triazole-ligand-based facial-homoleptic iridium complex. Single-crystal X-ray diffractometry results suggested that the complex is a facial isomer with C3 point symmetry. The complex exhibited a blue emission band centered at ∼450 nm in both solution and the film state at ambient temperature; moreover, it showed a very narrow full-width at half maximum value (55 nm) and a moderate photoluminescence quantum yield (33%). The complex showed high thermal stability, with 5%-weight-loss and glass-transition temperatures of 324 and 210 °C, respectively. Consecutive cyclic voltammetry measurements revealed outstanding electrochemical stability of the complex. Therefore, multilayer phosphorescent OLEDs that use IrTrz as the blue emitter were fabricated with two types of host material: (3,3′-di(9H-carbazol-9-yl)-1,1′-biphenyl (mCBP) and 9-(dibenzo[b,d]thiophen-4-yl)-9H-3,9′-bicarbazole (4DBTCz)). In particular, the 4DBTCz-based devices exhibited low turn-on voltages (∼5.0 V) and high external quantum efficiencies (>11%) with a Commission Internationale de l’Eclairage y-coordinate of 0.2. Moreover, the devices demonstrated stable operational lifetimes that exceeded 690 h (for mCBP) and 390 h (for 4DBTCz) at 100 cd/m2. Therefore, we believe that the 1,2,4-triazole-ligand-based Ir(III) complex is a promising blue-phosphorescent emitter material for applications in stable and efficient OLED devices.