Increase In Photoluminescence Intensity Research Articles

Carbon dots encapsulated in (YGd)2O3:Eu3+ nanophosphors for thermal sensing, advanced forensic and information security applications

The outstanding optical characteristics of carbon dots (CDs) make them an extremely promising class of multifunctional nanomaterials based on carbon. The incorporation of hydrothermally prepared Aloe vera carbon dots (AVCDs) into europium doped yttrium gadolinium ((YGd)2O3:Eu3+) mixed oxide nanophosphors ((YGO):Eu3+ NPs) synthesized through the solution combustion (SC) method. The resulting (YGO):Eu3+@AVCDs nanocomposite (NCs) demonstrates a broad excitation band, with the intense peak at ∼395 nm, aligning with the emission wavelength (350–420 nm) of n-UV LED chips. Notably, the (YGO):Eu3+@AVCDs (5 wt %) NCs exhibits a 4 fold increase in photoluminescence (PL) intensity compared to (YGO):7Eu3+, attributed to the fluorescence resonance energy transfer (FRET) between AVCDs and Eu3+ ions. Remarkably, even at an elevated temperature of 423 K, the thermal stability of (YGO):Eu3+@AVCDs (5 wt %) remains exceptional, retaining 88.31 % of its initial luminescence intensity. The internal quantum efficiency (IQE) is measured at a notable 74.16 %, while the optimized composite achieves a remarkable color purity of 99.59 %. Latent fingerprints (LFPs) are effectively developed on different surfaces using the optimized NCs via a simple powder dusting technique, and these fingerprints (FPs) revealed under 365 nm UV light. The study also examines various pore parameter namely size, shape, number, position, type, and inter-distance. Moreover, a transparent anti-counterfeiting (AC) ink is fabricated using optimized NCs providing effective AC features through its red emission under 365 nm UV light. This study not only offers solutions for overcoming the self-quenching effect of CDs but also underscores the potential applications in white light emitting diodes (w-LEDs), latent fingerprints, lip prints (LPs), and anti-counterfeiting.

Decolorization, spectral broadening, and luminescence enhancement in Tb:Y2O3 transparent ceramics through vacuum thermal reduction.

Tb3+ is extensively employed in magneto-optical devices and luminescent materials owing to its distinctive physical properties. However, under certain conditions, trivalent Tb3+ readily undergoes oxidation to tetravalent Tb4+, significantly reducing the performance of devices containing Tb3+. In this Letter, we report a technique called dual-annealing (DA) post-treatment, which effectively solves Tb oxidation issues by utilizing the reducibility of the vacuum environment. High-quality Tb:Y2O3 transparent ceramics were prepared with in-line transmittance of ∼80% at 800 nm. Subsequently, the prepared ceramics were subjected to DA treatment. The optical, photoluminescence, radioluminescence, and x-ray imaging properties of DA samples were comprehensively compared with those of conventionally single-annealed (SA) samples. The coloration of Tb:Y2O3 transparent ceramics due to Tb4+ absorption was eliminated by DA. Notably, the DA sample showed a 3.28-fold increase in photoluminescence intensity and a 2.73-fold increase in radioluminescence intensity compared with the traditional SA sample. DA post-treatment enables Tb: Y2O3 transparent ceramics to achieve x-ray imaging capabilities. This Letter presents a simple, efficient, and universally applicable post-treatment technique expected to replace conventional hydrogen annealing in numerous scenarios.

Regulating Surface Defects to Achieve More Positive Light Soaking Effect in Perovskite Solar Cells.

The dynamic defect tolerance under light soaking is a crucial aspect of halide perovskites. However, the underlying physics of light soaking remains elusive and is subject to debate, exhibiting both positive and negative effects. In this investigation, we demonstrated that surface defects in perovskite films significantly impact the performance and stability of perovskite solar cells, closely correlated with light soaking behaviors. Removing the top surface layer through adhesive tape, the surface defect density noticeably decreases, leading to enhanced photoluminescence (PL) efficiency, prolonged carrier lifetime, and higher conductivity. Consequently, the power conversion efficiency (PCE) of solar cells improves from 17.70% to 20.5%. Furthermore, we confirmed a positive correlation between surface defects and the light soaking effect. Perovskite films with low surface defects surprisingly exhibit a 3-fold increase in PL intensity and an 85% increase in carrier lifetime under 500 s of continuous illumination at an intensity of 100 mW/cm2. Beyond the conventional strategy of suppressing defect trapping, we propose increasing the capability of dynamic defect tolerance as an effective strategy to enhance the optoelectronic properties and performance of perovskite solar cells.

Optically addressable spin defects coupled to bound states in the continuum metasurfaces

Van der Waals (vdW) materials, including hexagonal boron nitride (hBN), are layered crystalline solids with appealing properties for investigating light-matter interactions at the nanoscale. hBN has emerged as a versatile building block for nanophotonic structures, and the recent identification of native optically addressable spin defects has opened up exciting possibilities in quantum technologies. However, these defects exhibit relatively low quantum efficiencies and a broad emission spectrum, limiting potential applications. Optical metasurfaces present a novel approach to boost light emission efficiency, offering remarkable control over light-matter coupling at the sub-wavelength regime. Here, we propose and realise a monolithic scalable integration between intrinsic spin defects in hBN metasurfaces and high quality (Q) factor resonances, exceeding 102, leveraging quasi-bound states in the continuum (qBICs). Coupling between defect ensembles and qBIC resonances delivers a 25-fold increase in photoluminescence intensity, accompanied by spectral narrowing to below 4 nm linewidth and increased narrowband spin-readout efficiency. Our findings demonstrate a new class of metasurfaces for spin-defect-based technologies and pave the way towards vdW-based nanophotonic devices with enhanced efficiency and sensitivity for quantum applications in imaging, sensing, and light emission.

Low-energy-consumption rapid synthesis of carbon dots at room temperature from combusted food waste with versatile analytical applications

In this study, we developed a low-energy-consumption green method for synthesising carbon dots (CD) at room temperature using watermelon rind as the carbon source through a cutting process based on NaCl crystals. The synthesis process was rapid (<5 min) and facile. The synthesised CD were characterised using photoluminescence (PL) spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The results revealed that the synthesised dots exhibited robust adsorption, a spherical shape and a uniform size distribution. The PL intensity of the quantum dots decrease due to the temperature rising, metal ions and ponceau 4R added. In contrast with PH, PL intensity increase, so these CD can serve as multifunctional sensing materials. Overall, this study presents an environmentally friendly method for the rapid synthesis of CD that are suitable for temperature, pH, metal ion and food sensing applications.

In situ doping effect in monolayer MoS2 via laser irradiation

Abstract Two-dimensional (2D) semiconducting materials with a single atomic layer display exceptional structural symmetry and band structures, making them the most promising candidates for investigating the spin-valley coupling effect and fabricating novel optoelectronic devices. Their atomic thinness also makes it easy to adjust their excitonic optical response through plasma treatment or thermal annealing. In this study, we present a simple technique for modifying the optical properties of monolayer MoS2 by briefly exposing it to laser irradiation in ambient conditions. Initially, this exposure resulted in a nearly twofold increase in photoluminescence (PL) intensity, with the neutral exciton intensity increasing while the trion exciton intensity decreased. We propose that oxygen-related functional groups, such as O2 and H2O from the surrounding air, adsorb onto MoS2 and extract extra electrons, which enhances exciton emission while reducing trion emission. In a subsequent stage, both exciton intensities decreased as all extra electrons were depleted. Additionally, any structural distortions or potential damage were found to decrease the PL intensity, and these changes were linked to alterations in the Raman spectra.

Metal-Dictated Reactivity of Z-Type Ligands to Passivate Surface Defects on CdSe Nanocrystals.

Accessing semiconductor nanocrystals free from surface defects is an outstanding challenge in the design of materials with targeted properties. Despite the established importance of Z-type ligand surface passivation to eliminate defects, the optical and electronic properties of nanocrystals vary depending on the nanocrystal composition and Z-type ligand identity. In this work, a series of Cd-, Zn-, and Pb-based non-native Z-type ligands with the formula MX2 (X = undecylenate or chloride) were employed to elucidate Z-type ligand characteristics that result in surface passivation of undercoordinated surface ions to eliminate trap states from CdSe nanocrystals. First, CdSe nanocrystals were reacted with N,N,N',N'-tetramethylethylene-1,2-diamine (TMEDA) to remove native Cd(oleate)2 Z-type ligands from the surface, resulting in undercoordinated surface chalcogen ions. After subsequent reaction with M(UDA)2, ligands bound to the surface were quantified by NMR spectroscopy, and in parallel, the impact of Z-type ligands on the nanocrystal optical properties was monitored using photoluminescence spectroscopy. We find that Cd- and Zn-based Z-type ligands exhibit similar reactivity with the nanocrystal surface via NMR spectroscopy, yet Cd(UDA)2 passivation results in an 800% PL increase while Zn(UDA)2 passivation yields a 13% increase in photoluminescence intensity. Nanocrystals reacted with Pb-based Z-type ligands have lower surface coverage, as quantified by NMR spectroscopy, and lead to only a marginal increase of nanocrystal photoluminescence intensity (60%). These data indicate that the metal identity of the Z-type ligand has a profound impact on the reactivity and resulting electronic structure of the postsynthetically modified nanocrystal. This work provides a framework for achieving defect-free CdSe nanocrystals.

Spinel Phase Engineering Boosted Visible-Light Photocatalytic Activity in Co1-xSrxCr2O4.

We synthesized Sr-doped spinel CoCr2O4 using the solution combustion method and characterized the structure, morphology, chemical state, and photocatalytic properties through different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrochemical impedance spectroscopy (EIS). 30-50 nm cuboid CoCr2O4 nanocrystals with Sr doping levels ranging from 0 to 0.6% were obtained; the increasing Sr doping deformed the coordination number of Co and Cr, transitioning to octahedral and tetrahedral units, inducing the phase transition from spinel to inverse spinel at 0.6% Sr content. This modification enhanced optical absorption, reduced the energy band gap, increased photoluminescence intensity, and maintained a high-spin state with oxygen vacancies. 0.6% Sr-doped CoCr2O4 demonstrated the highest photocatalytic efficiency at 93%. The XRD structure and photocatalytic activity remained at 87% over 7 cycles after 14 h. Employing degradation pathways and Mott-Schottky curves elucidated the enhancement mechanism.

Ordered hierarchical superlattice amplifies coated-CeO2 nanoparticles luminescence

Achieving a controlled preparation of nanoparticle superstructures with spatially periodic arrangement, also called superlattices, is one of the most intriguing and open questions in soft matter science. The interest in such regular superlattices originates from the potentialities in tailoring the physicochemical properties of the individual constituent nanoparticles, eventually leading to emerging behaviors and/or functionalities that are not exhibited by the initial building blocks. Despite progress, it is currently difficult to obtain such ordered structures; the influence of parameters, such as size, softness, interaction potentials, and entropy, are neither fully understood yet and not sufficiently studied for 3D systems. In this work, we describe the synthesis and characterization of spatially ordered hierarchical structures of coated cerium oxide nanoparticles in water suspension prepared by a bottom-up approach. Covering the CeO2 surface with amphiphilic molecules having chains of appropriate length makes it possible to form ordered structures in which the particles occupy well-defined positions. In the present case superlattice arrangement is accompanied by an improvement in photoluminescence (PL) efficiency, as an increase in PL intensity of the superlattice structure of up to 400 % compared with that of randomly dispersed nanoparticles was observed. To the best of our knowledge, this is one of the first works in the literature in which the coexistence of 3D structures in solution, such as face-centered cubic (FCC) and Frank-Kasper (FK) phases, of semiconductor nanoparticles have been related to their optical properties.

Improving photoluminescence properties and reducing recombination of CsPbBr3 perovskite through lithium doping.

This study investigates the impact of lithium doping on the structural and photophysical properties of spin-coated CsPbBr3 perovskite thin films. The deposited films display a pristine structure, preferentially growing along the (220) direction, and exhibit high-quality green photoluminescence at around 530 nm. The doping leads to an improvement in the optical properties of the films, as evidenced by a stronger photoluminescence (PL) intensity compared to undoped CsPbBr3, particularly at temperatures below 200 K. The increase in PL intensity suggests a decrease in defects and surface passivation. Additionally, the decrease in the power-law exponent β from 1.6 to 1.0 indicates a reduction in non-radiative recombination, likely due to trap states filling with free electrons induced by the doping. Overall, doping with lithium reduces non-radiative recombination, fills trap states, and reduces band tail/activation energy, leading to improved optoelectronic properties of the films. This investigation provides insights into the photophysical properties of the Li-CsPbBr3 absorber layer and the recombination mechanism, and helps to unravel new methods for the development of high-stability, high-performance perovskite thin-film solar cells and optoelectronic devices.

Deep-red photoluminescent mechanoresponsive polymers with dynamic CuI-arylamide mechanophores.

We demonstrate the use of copper arylamide complexes as efficient photoluminescent mechanophores to design deep-red/near-IR emissive polymers showing reversible changes in photoluminescence intensity in the red/near-IR region in response to mechanical stretching. The mechanoresponse was repeatable over 30 cycles, showing a measurable increase of photoluminescence intensity even at a small applied stress of ca. 0.01 MPa. We demonstrate the potential of using conformationally dynamic copper amide complexes as sensitive and reversible mechanophores for near-IR imaging; systematic control over the emission range was achieved using amide modification.

Controlling photoluminescence of silicon quantum dots using pristine-nanostates formation

This study investigates the effective control of photoluminescence (PL) of silicon nanocrystals (Si–NCs) embedded in a SiO2 matrix, with a specific focus on tuning the luminescent wavelength profile and intensity for silicon-based optoelectronic applications. By manipulating the composition ratio (x) of SiOx, the well-known simultaneous changes in PL peak position and intensity were observed after annealing. To preserve the desired wavelength characteristics and enhance the luminesce intensity, we propose a novel approach to generate pristine nanostates (PNs) for Si-NC formation using proton irradiation (PI). The application of proton irradiation was found to be successful in significantly increasing PL intensity while strongly suppressing the peak position shifts. Through extensive spectroscopic analysis including PL, X-ray photoelectron spectroscopy, and absorption spectroscopy, we investigate specific defect states in the SiOx matrix, and identified as PNs. We interpret that these PNs consist of self-trapped exciton, E′ center, non-bridging oxygen hole center, and oxygen-deficiency center states. In the as-grown sample, the PNs promote appropriate phase separation and play a significant role in stabilizing the structure during the subsequent annealing processes. This study elucidates the Si-NC formation mechanism by enhancing O-diffusion-induced phase separation, a process accelerated in SiOx with controlled PNs. The proposed PI-induced PNs offer a novel pathway for developing Si-based optoelectronic devices with desired characteristics in the operating wavelength range. These findings open up promising possibilities for advanced silicon-based optoelectronic applications.

Surface modification of ZnO nanowires using single walled carbon nanotubes for efficient UV–visible broadband photodetection

A UV–visible broadband photodetector (PD) based on single walled carbon nanotube (SWCNT)/Zinc oxide nanowire (ZnO NW) hybrid is being reported. This work focuses on designing a stable, fast, efficient and reliable hybrid broadband PD by surface modification of ZnO NWs using SWCNT. The study shows that spectral response of the hybrid heterostructure (HS) spans beyond the UV spectrum and into the visible region which is due to the integration of SWCNTs. Photoluminescence (PL) study reveals surface plasmon (SP) mediated resonance phenomenon resulting in an increase in PL intensity. High nanotube charge carrier mobility and conductivity allows the hybrid HS to attain high values of spectral responsivity (R λ = 187.77 A W−1), external quantum efficiency (EQE = 5.82 × 104%), specific detectivity (D* = 7.04 × 1011 Jones) and small noise equivalent power (NEP = 4.77 × 10−12 W) values for the SWCNT/ZnO NW hybrid HS. The device also gives quick rise (t rise = 0.43 s) and fall (t fall = 0.60 s) time values.

Investigation of Surface Nanoclusters and Paramagnetic Centers of ZnO/Por-Si Structures as the Basis of Sensory Properties

The detection of particles with uncompensated charge and the determination of the features of their interaction during the formation of nanocrystals on substrates with a developed surface are an interesting area of research. The porous surface formed via the electrochemical etching of silicon acquired fractal properties as a result of the deposition of zinc oxide layers. Microscopy methods using different resolutions revealed a hierarchical structure of the surface, where each of the three consecutive levels contains uniformly distributed formations. The deposition of 20 layers of ZnO maximizes the concentration of nanocrystals at the pore boundaries, while the deposition of 25 layers leads to the formation of a continuous layer. The increase in photoluminescence intensity with an increase in the number of deposited layers is due to the saturation of surface nanostructures with electrons through several mechanisms. Electron paramagnetic resonance (EPR) studies have shown that the main mechanism of radiation recombination is the capture of electrons on oxygen vacancies. The different nature of the EPR saturation of the signal of interconnected paramagnetic centers revealed the formation of zinc oxide particles at the boundaries of pores with different sizes. The results of these studies of surface-active structures effectively complement the knowledge about sensory materials.

What is TADF (thermally activated delayed fluorescence) compared to the mechanisms of FL (fluorescence), PH (phosphorescence), and TTA (triplet–triplet annihilation) based on a novel naphthalimide sulfonylphenyl derivative as a host?

One of the biggest challenges in the field of optoelectronics is to easily identify the mechanisms involved in light-emitting materials. There are several different mechanisms of emission, and the best known are fluorescence (FL), phosphorescence (PH), thermally activated delayed fluorescence (TADF), and triplet–triplet annihilation (TTA). In this study, simple ways to diagnose these mechanisms are presented with an example. N,N-di(benzenesulfonylphenyl)-N-(N-2-aminomethylpyridine-1,8-naphthalimide)amine is synthesized as a host compound due to its high HOMO-LUMO and ionization potential (IP) values and three emitters consisting of 50 wt% Bis (1phenylisoquinoline))(acetylacetonate)iridium(III) (Ir(piq)2(acac)), 10-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) and 1,1′-(2,5-Dimethyl-1,4-phenylene)dipyrene (DMPPP) were considered. Overall, the host compound, doped Ir(piq)2(acac) and doped DMPPP follow the mechanisms of FL, the combination of FL and PH, and the combination of FL and TTA, as the photoluminescence (PL) decay life time and the PL intensity increased with decreasing temperature. However, DMAC-TRZ doped with the host compound showed the TADF mechanism, as the PL decay lifetime and the PL intensity increase simultaneously with increasing temperature. In addition, the difference between the singlet excited state (S1) and the triplet excited state T1 (ΔEST) from the PL and PH spectra at 77 K for the spin-coated DMAC-TRZ-doped host show the lowest value in between the samples at 0.02 eV, and the reverse intersystem crossing (rISC) effect is activated. Moreover, the linear slopes of the power dependence analysis of the DMPPP-doped host were calculated to be 2.04 and 0.91, indicating that there are two components (photons) for this sample which is strong evidence for the TTA mechanism. Taking into account the synthesized host compound, (Ir(piq)2(acac):host), (DMAC-TRZ:host) and (DMPPP:host) as emitter layers, the organic light emitting diodes (OLEDs) were fabricated via solution processing, and the TADF OLED exhibited the highest efficiency among the other OLEDs.

Simultaneous enhancement of red luminescence and thermal stability of a novel red phosphor: A Li+-Eu3+ co-occupied site strategy in BaAl2Ge2O8 lattices

The rapid development of phosphor-converted white light emitting diodes (pc-WLEDs) requires new red phosphors with efficient and thermally stable luminescence for high-quality warm-white lighting. However, it is still a challenge to discover red phosphors with facile synthesis, high internal quantum efficiency (IQE), excellent thermal stability and high color purity. Herein, a novel red-emitting Eu3+ activated barium dialuminum digermanate (BaAl2Ge2O8, BAGO) phosphor showing strong red emission at 610 nm was prepared. The IQE is improved from 32.91% to 78.84% by employing a charge compensation strategy. The lithium-ion co-doped BAGO:Eu3+ phosphor exhibits a nearly twofold increase in integral photoluminescence (PL) intensity and the high color purity reaches 94.17%. Impressively, the PL intensity of the BAGO:Eu3+,Li+ phosphor drops by only 2.6% at 150 °C of that at room temperature. Finally, the pc-WLED using the red BAGO:Eu3+,Li+ phosphor exhibits white light with the chromaticity coordinate of (0.3515, 0.3495), a high color-rendering index of 92 and a low correlated color temperature of 4746 K. All these results manifest that BAGO:Eu3+,Li+ phosphor is a suitable red phosphor for near-ultraviolet (NUV) chip-based pc-WLEDs.

Nonclassical Mechanism of Metal-Enhanced Photoluminescence of Quantum Dots.

Metal-enhanced photoluminescence is able to provide a robust signal even from a single emitter and is promising in applications in biosensors and optoelectronic devices. However, its realization with semiconductor nanocrystals (e.g., quantum dots, QDs) is not always straightforward due to the hidden and not fully described interactions between plasmonic nanoparticles and an emitter. Here, we demonstrate nonclassical enhancement (i.e., not a conventional electromagnetic mechanism) of the QD photoluminescence at nonplasmonic conditions and correlate it with the charge exchange processes in the system, particularly with high efficiency of the hot-hole generation in gold nanoparticles and the possibility of their transfer to QDs. The hole injection returns a QD from a charged nonemitting state caused by hole trapping by surface and/or interfacial traps into an uncharged emitting state, which leads to an increased photoluminescence intensity. These results open new insights into metal-enhanced photoluminescence, showing the importance of the QD surface states in this process.

Synthesis, characterization and enhanced photoluminescence and temperature dependence of ZrO2:Dy3+ phosphors upon incorporation of K+ ions

This study reports the successful synthesis and comprehensive characterization of ZrO2:Dy3+ phosphors with the incorporation of K+ ions. The introduction of Dy3+ and K+ in the ZrO2 lattice as lanthanide activators demonstrates its potential as an efficient host material. The structural integrity of ZrO2 remains unaltered following the doping process. Fourier-transform infrared spectroscopy (FTIR) analysis confirms the presence of Zr-O and O-H stretching, along with H2O bending modes in the phosphor sample. The wide luminescence band seen at 460 nm is attributed to luminescence defects in the ZrO2 induced by oxygen, and the presence of water molecules. Photoluminescence (PL) spectra analysis reveals pronounced emission peaks at 491 and 578 nm, corresponding to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions, respectively, upon excitation at 349 nm. Optimizing the Dy3+ doping concentration to 0.4 wt% and achieving a critical distance of 31.82 Å resulted in efficient energy transfer. Notably, co-doping K+ as a charge compensator significantly enhances the luminescence intensity. Moreover, at lower temperatures, direct excitation of Dy3+ ions through our pump wavelength, coupled with exciton-mediated energy transfer, leads to a remarkable increase in PL intensity. Tailoring the doping concentrations effectively shifts the emission spectrum of the phosphor mixture, aligning with the standard white light illumination coordinates (0.333, 0.333). This property positions the material as a promising candidate for applications in white light-emitting diodes (WLEDs) and various high-quality lighting applications. The enhanced photoluminescence and temperature dependence observed in ZrO2:Dy3+ phosphors upon the incorporation of K+ ions pave the way for their potential utilization in advanced luminescent devices.

Tunable luminescence and energy transfer in Tb3+,Eu3+ co-doped Gd2Zr2O7 phosphors with high thermal stability for WLEDs

Red phosphors with good thermal stability, high color temperature and color purity are critical in high power warm white LED devices. Herein, a series of single and co-doped Tb3+,Eu3+ polychromatic phosphors with pyrochlore structure based on Gd2Zr2O7 have been prepared for the first time by a conventional solid phase reaction method. Compared to single doped Eu3+ phosphors, Tb3+,Eu3+ co-doped phosphors possess following advantages: improved UV absorption, increased photoluminescence intensity, extended luminescence range and improved thermal stability. At room temperature, the Gd2Zr2O7:Tb3+,Eu3+ phosphors exhibited a gradual shift from yellow-green emission at 544 nm to orange-red emission at 613 nm with increasing doping of Eu3+ ions. Energy transfer efficiency has been evaluated to be 71% by analyzing the fluorescence lifetime of Tb3+ ions. The concentration quenching mechanism under different conditions was analyzed in detail and it was concluded that the quenching of Tb3+ is caused by dipole-dipole interaction. In addition, the activation energy (ΔEa) of the Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphor was calculated to be as high as 0.2674 eV compared to other Tb3+, Eu3+ co-doped phosphors, demonstrating its high thermal stability. WLEDs devices based on Gd1.92Zr2O7:0.03Tb3+,0.05Eu3+ phosphors have been prepared, which have low correlated color temperature (CCT) (5283 K), high color rendering index Ra = 85.5 K) and CIE coordinates chromaticity coordinate (0.3371,0.3333). All of the results show that Gd2Zr2O7:Tb3+,Eu3+ phosphors provide a new avenue to develop high quality red emission and high thermal stability phosphors for WLEDs.

Simple Thermal Annealing‐Assisted Direct Synthesis and Optical Property Study of CuO Nanoparticles Incorporated Polyvinyl Alcohol Films

This article reports a simple thermal annealing‐assisted direct synthesis method to prepare copper oxide (CuO) nanoparticles incorporated in polyvinyl alcohol (PVA) films and a systematic study of their optical properties. CuO‐PVA nanocomposite films are prepared with a different weight percentage of CuO in the PVA matrix. Scanning electron microscopy (SEM), X‐ray diffraction (XRD), UV‐visible spectroscopy, and photoluminescence spectroscopy are employed to study the prepared films. XRD confirms the formation of crystalline CuO nanoparticles in PVA, while the SEM analysis shows uniformly distributed spherical nanoparticles in PVA. The findings show that thermal annealing at a mild temperature plays a crucial role in improving the crystallinity and optical properties of the nanocomposite film. In comparison to PVA, CuO‐PVA nanocomposite exhibits improved absorption with a new absorption band in the lower wavelength region. The nanocomposite samples excited with 300 nm show intense photoluminescence (PL) at 365 nm and an increase of PL intensity with CuO concentration in the PVA matrix. In contrast, samples excited with 425 nm show green emission at 550 nm in the visible region of the electromagnetic spectrum. The PL in CuO‐PVA nanocomposites can be originated due to the transitions associated with acceptor and donor defects in the material. The study opens up a new route to fabricate CuO‐PVA nanocomposites with superior optical properties.