Yellow Emission Band Research Articles

Cool white light emitting Dy3+ activated KNaCa2(PO4)2 phosphor for outdoor lighting and optical thermometric applications

Dy3+ incorporated KNaCa2(PO4)2 phosphor (KNCP) with doping concentrations ranging from 0.005 to 0.7 mol were synthesised via high-temperature solid state reaction route. The morphological characteristics were examined using FESEM images and found agglomerated structure in micrometers with an average particle size of 4.037 µm. Photoluminescence emission spectra under 350 nm excitation reveal nearly equal intense blue and yellow emission bands owing to 4F9/2→6H15/2 and 4F9/2→6H13/2 Dy3+ transitions, respectively. The concentration-dependent emission properties were examined and the optimum concentration was found to be 0.03 mol. The synthesized phosphor exhibits a quantum yield of 69.06 % at the optimal Dy³⁺ doping concentration. The time-correlated emission characteristics were analysed from the TRES plot. Furthermore, the emission bands at 479 nm (4F9/2→6H15/2) and 572 nm (4F9/2→6H13/2) under 350 nm excitation follow bi-exponential decay having an average lifetime in the range of 0.90–0.37 ms. The prepared phosphors exhibit an intense cool white light regardless of doping concentration and delay time. Optical thermometric properties of KNCP Dy phosphor were investigated by fluorescence intensity ratio (FIR) technique and exhibit relative thermal sensitivity of 2.57 and 0.7 %K−1 in the temperature range of 90 −230 K and 250–500 K respectively. The excellent quantum yield, sub-millisecond lifetime, cool colour temperature, and higher temperature sensitivities make them ideal for outdoor lighting and optical thermometric applications.

Effect of samarium oxide addition on the structural, thermal, and optical properties and photoluminescence of lithium borate glass

The samples were prepared in compliance with the form 33 Li2O–66 B2O3—(1-x) AgF—x Sm2O3, where x = 0, 0.25, 0.5, and 0.75. Powdered samples were converted to a glassy state via melting and quenching. The glassiness of the prepared samples was examined using X-ray diffraction (XRD) and Differential Thermal Analysis (DTA). From the absorption spectra of the prepared glass samples, the band gap in the optical spectrum changed slightly in the range of 3.45, whereas the Urbach energy decreased from 0.32 to 0.267 eV. The fluctuations of the optical band gap and Urbach energy can be attributed to variations in the glass structure. Sm3 + emitted intense reddish-orange light under blue and UV light excitation. There are six excitation bands in the Sm3+ excitation spectrum situated in the blue and UV regions, peaking at 361.7, 374, 400, 417, 462, and 475 nm, which are attributed to the transitions from 6H5/2 to 4D3/2, 6P7/2, 6P3/2, 6P5/2, 4I13/2, and 4I11/2 respectively. The transition from 6H5/2 to 6P3/2 had the highest intensity and was associated with a peak at 400 nm. The bright yellow, reddish-orange, and red emission bands of the Sm3+ ions in the oxide glasses are related to the 4G5/2 → 6H5/2, 4G5/2 → 6H7/2, and 4G5/2 → 6H9/2 emission transitions, respectively.

Influence of annealing temperature and laser irradiation on the structural, optical, and photoluminescence characteristics of Ni2O3/SnO2 nanocomposites for perspective applications

In this study, a new approach methodology is employed to modify the structural, optical, and photoluminescence properties of Ni2O3/SnO2(NO/TO) nanocomposites. The effects of temperature and laser irradiation on a specific system were analyzed and described using XRD, XPS, and TEM. The diffraction patterns indicate the presence of two distinct phases within the NO/TO system. The XPS results reveal a robust underlying interaction between Ni2O3 and SnO2, exhibited by the observed shifts in the peak positions of Ni 2p, Sn 3d, and O 1 s. The TEM images demonstrate the formation of hexagonal and half-hexagonal forms with varying orientations, as well as the emergence of elongated tetragonal shapes, upon increasing the temperature to 900 °C. the notable enhancement in light absorption, with the absorption bands spanning a wide range in the UV–vis spectra, specifically from approximately 300 nm to around 800 nm in the near-infrared (NIR) region. The broad range of PL emission bands identified by this mixture of nanoparticles, expanding from the UV to the near and intermediate IR regions, demonstrated that NO/TO nanocpomposites are considerably defective. The NO/TO nanocomposites exhibit efficient multi-color band emissions at ambient conditions, rendering them promising contenders for deployment in optoelectronic nanodevices, including blue, yellow, and white band emission light-emitting diodes and NIR luminescence bioimaging.

Large‐Scale Room‐Temperature Synthesis of the First Sb3+‐Doped Organic Ge(IV)‐Based Metal Halides with Efficient Yellow Emission for Solid‐State Lighting and Latent Fingerprint Detection

Organic–inorganic hybrid Ge(II)‐based metal halides have garnered significant interest due to their intriguing photophysical properties and environmentally friendly characteristics. However, challenges such as poor stability, low emission intensity, and a complex synthesis process have hindered their widespread application. In addressing these issues, a breakthrough in the large‐scale production of Sb3+‐doped Ge(IV)‐based metal halide (C13H14N3)2GeCl6 phosphors at room temperature through a straightforward solution method is presented. The synthesized compound exhibits a remarkable bright broad yellow emission band at 590 nm, boasting a photoluminescence quantum efficiency of 99.53 ± 0.06% the highest among Ge(IV)‐based metal halides. Notably, the introduction of Sb3+ induces the formation of Jahn–Teller‐like self‐trapped excitons in [SbCl6]3− species, attributable to lattice distortion and strong electron–phonon coupling. Consequently, Sb3+‐doped (C13H14N3)2GeCl6 demonstrates a large Stokes shift (221 nm) and a prolonged decay lifetime (3.06 μs). Furthermore, the Sb3+‐doped compound exhibits commendable chemical‐ and photostability, prompting exploration in applications such as white light‐emitting diodes and latent fingerprint detection. This work not only provides a practical approach for designing economically viable, environmentally friendly, and highly efficient emission phosphors but also paves the way for novel directions in their expanded application.

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.

Broadband emission characteristics and WLED application of self-activated YMZn3AlO7 (M=Ca, Sr, Ba) phosphors

In this study, a non-activated ion-doped full-spectrum emission phosphor for white light-emitting diode (WLED) lighting is proposed using oxygen defect engineering. The YMZn3AlO7 (M = Ca, Sr, Ba) phosphors with "114″ structure were prepared via a high-temperature solid-state reaction. Under excitation with 373 nm ultraviolet (UV) light, YSrZn3AlO7 in YMZn3AlO7 (M = Ca, Sr, Ba) exhibited the highest emission intensity and formed a wide yellow emission band centred at 563 nm. The full width at half maximum of the YSrZn3AlO7 phosphor was 172.6 nm. A theoretical model based on the designed oxygen vacancies was proposed to determine the self-activated luminescence mechanism. Density functional theory calculations revealed that oxygen vacancies lead to the generation of new energy levels. Electron paramagnetic resonance experiments further confirmed that the luminescence originated from oxygen vacancies. Eventually, a warm WLED device ((x, y) = (0.4057, 0.4359)) with a correlated color temperature of 3814 K and a relative color rendering index of 83 was successfully prepared using the YSrZn3AlO7 phosphor and a 365 nm UV LED chip. These results suggest that YSrZn3AlO7 is a promising WLED phosphor and provide new insights into the application of self-activated phosphors in WLED.

Role of defects in tailoring optical, electronic, and luminescent properties of Cu-doped ZnO films

We present a detailed characterization study on copper-doped ZnO films to correlate the films' electronic and optical properties with the existing native defects in the lattice. In addition, we describe the variation in the concentration of these defects with Cu dopant and temperature. The results of XRD confirmed the single-phase würtzite-structure of the synthesized films. The SEM images showed a homogeneous and dense grain morphology with a granular form and a signature for a hexagonal-like shape. The EDX, XPS, and UV–Vis spectra showed the proper doping of Cu ions into the lattice. The XPS analysis indicated mixed electronic states of both Cu2+ and Cu1+ and showed a clear increase in the Cu2+ intensity relative to Cu1+, with Cu dopant. The transmittance spectra exhibited an average value above 80% in all doped films in the visible and infrared regions. The overall results indicated a clear link between the films’ optical and electronic responses and the level of the intrinsic defects in the lattice. By increasing the Cu dopant, we find a slight reduction in the energy bandgap (Eg). This is correlated with a clear reduction in the blue emission luminescence band associated with the VZn and in the yellow emission band associated with the Oi. On the other hand, we observed a clear enhancement in the green emission band originating from the VO, and in the emission band related to possible transitions from Zni levels to Oi levels. The slight reduction in the Eg signals a weak sp-d hybridization between the ZnO conduction band electrons and the Cu2+ ions, which is mediated by the intrinsic defects. With reducing the temperature, the photoluminescence temperature profiles indicated a slight increase in the Eg values and a negligible effect on the distribution of the native defects.

Rhodamine Derivative-Linked Silica-Coated Upconverting Nanophosphor (NaYF4: Yb3+/Er3+@SiO2-RBDA) for Ratiometric, Ultrasensitive Chemosensing of Pb2+ Ions

Lead (Pb2+) ions are considered as one of the primary environmental pollutants and have a profound effect on human health. In this work, we have developed a hybrid organic–inorganic optical nanochemosensor for selective and ultrasensitive detection of Pb2+ ions based on energy transfer (ET), involving a Pb2+ sensitive rhodamine-derived named (E)-4-(((3′,6′-bis(diethylamino)-3-oxospiro[isoindoline-1,9′-xanthen]-2-yl)imino)methyl)benzaldehyde represented as RBDA, covalently linked with silica coated upconverting nanophosphors (UCNPs). The UCNPs emit visible light after being excited by NIR light, activating the Pb2+ coordinated RBDA (fluorescent probe). When Pb2+ ions were added, a yellow emission band at about 588 nm formed in upconverting photoluminescence spectra, whereas the strength of green emission at about 542 nm reduced upon excitation of 980 nm laser, indicating the energy transfer from UCNP to RBDA-Pb2+ complex. The concentration of Pb2+ ions directly affects how well the probe reabsorbs the green emission of the nanophosphor, thus enabling the ratiometric chemosensing. With a detection limit of 20 nM in aqueous, the resulting ET-based nochemosensor can also preferentially detect Pb2+ despite the presence of other ions. Owing to the minimal autofluorescence and the great penetration depth of NIR light and special optical features of UCNPs, this is a promising approach for sensitive and in-depth detection of Pb2+ ions in a complex ecological and biological specimen.

Correlation between structural and optical properties of Dy[formula omitted] doped BaGd[formula omitted]O[formula omitted] phosphors intended for solid-state lighting applications

Highly crystalline and single phase BaGd2−xDyxO4 (0.00 ≤x≤ 0.16) phosphors, with an average crystallite size around 126 nm, have been synthesised using solid-state reaction technique. The structural and optical properties of these phosphors have been studied in detail to establish an unambiguous correlation between these properties. High-angle annular dark field (HAADF) images have confirmed that the constituent elements are homogeneously distributed in the particles, and their elemental composition has been established using X-ray photoelectron spectroscopy (XPS). The tuning of optical band gap with x has been achieved, which is a rare achievement in these phosphors. Also, the optimum concentration of Dy3+ ions has been found to be 0.8 mol%, which is the lowest among the Dy3+ doped BaGd2O4 phosphors reported so far. This concentration quenching effect has been discussed on the basis of a combination of decay curve analysis, calculation of average critical distance between the Dy3+ ions and integrated intensities of photoluminescence (PL) emission bands. The average crystallite size and optical band gap has also been found to decrease after x = 0.016, from which their correlation with concentration quenching effect has been investigated. The asymmetry ratio between the integrated intensities of yellow and blue PL emission bands has been observed to be greater than 2 throughout x, which confirmed the preferential lattice site for Dy3+ ions in these phosphors with present synthesis conditions. The variation of asymmetry ratio and Gd3+-dominated IR-active lattice vibrations with x, and Vegard’s law pertaining to the volume of a unit cell confirms that the local bonding environment in the lattice of these phosphors gets modified at x = 0.016. The photometric parameters for these phosphors reveal their suitability for fabrication of warm light orange LEDs on appropriate UV chips.

One-Step, In Situ Hydrothermal Fabrication of Cobalt-Doped ZnO/CdS Nanosheets for Optoelectronic Applications

An in-situ hydrothermal process was used to create Co-doped ZnO/CdS nanosheets in order to examine the effects of the divalent impurity (Co) ions on the structural, morphological, optical, and magnetic characteristics of the test material. For both ZnO and CdS, XRD verified the development of a hexagonal wurtzite structure. SEM, TEM, and HR-TEM studies produced sheet-like morphology. Elemental mapping and XPS examination verified the presence of essential elements (S, Cd, O, Co, and Zn). Co-doping dramatically increased the nanosheets’ ability to absorb light in the visible area. Comparing the bandgap energy to pure ZnO and ZnO/CdS nanocomposites, the bandgap energy (2.59 eV) was well-regulated. The PL spectrum at 577 nm showed a prominent yellow emission band that was attributed to the 4A2g(F) → 4T1g(F) transition. Improvement in the room temperature ferromagnetic properties was observed due to doping of Co2+ ions. Warm white light harvesting was confirmed by the estimated CCT value (3540 K). The test material appears to be suitable for the creation of next-generation optoelectronic devices.

Crystalline native defects in ZnO analyzed by photoluminescence applying Maxwell-Boltzmann statistics in the visible region

Zinc oxide (ZnO (s) ) is prepared by Chemical Bath Deposition. This manuscript continues with previous research examining the Photoluminiecence at UV-Vis-region. According to emission bands situated at Vis-region by means of Photoluminescence, green (GE) and yellow emission (YE) bands are discussed, which are associated with native intrinsic crystalline defects. The Photoluminescence dependence with the trap density and the surface recombination velocity in the light of the Maxwell-Boltzmann theoretical model (MBM) results associated with the electronic transitions related to the native intrinsic defects situated at9 Vis-region are investigated. The trap density (cm -1 ) of nanocrystals located at range ~8.9-9.9 An approximate a theoretical-experimental kinetic model is presented, considering that the coordination complex ion is a key parameter in the crystal growth of ZnO (s) nanocrystals. The optimized geometry of [Zn(NH 3 ) 4 ] 2+ molecule was obtained with the DFT method using the functional of H-GGA B3LYP.

Photoluminescence and energy transfer studies on Tm3+/Dy3+/Eu3+doped borosilicate glasses for color tunability and warm white light generation

Potassium Zinc Alumino Borosilicate (KZABS) glasses doped with Dy3+, Tm3+ and Eu3+ have been prepared by a quench melting technique. The glasses show characteristic blue (1D2 → 3F4) and yellow (4F9/2 → 6H13/2) emission bands under 362 nm excitation. To produce warm white light, a red component was required in luminescence for which Eu3+ ions were added to the KZABS glass. A red emission (5D0 → 7F2) was seen under 362 nm excitation along with the blue and yellow bands. Photoluminescence (PL) studies show energy transfer from Tm3+ and Dy3+ ions to Eu3+ ions. The average lifetimes of the tri-doped glasses for all emission wavelengths decrease with increasing concentration of Eu3+ions. CIE chromaticity study also proves that tri-doped KZABS glasses can generate warm white light. Thus, we propose to use KZABS: Tm3+/Dy3+/Eu3+ glasses for warm white light generation in solid-state lighting (SSL) and white light emitting diode (w-LED) applications.

Powder synthesis and luminescence of a novel yellow-emitting Ba5Si11Al7N25: Eu2+ phosphor discovered by a single-particle-diagnosis approach for warm w-LEDs

White LEDs combined by blue LED chip and yellow YAG: Ce phosphor are the mainstream of the lighting industry. However, due to the lack of red light component, it is difficult to meet the requirements of warm white lighting. The novel needle-like Ba5Si11Al7N25:Eu2+ particle discovered by the single-particle-diagnosis method shows a broad yellow emission band centered at ∼570 nm and a FWHM of 98 nm. Compared with YAG: Ce phosphor, the novel Ba5Si11Al7N25:Eu2+ phosphor exhibits longer emission wavelength, indicating potential application in warm white LEDs. In this work, the phase-pure powder of Ba5Si11Al7N25:Eu2+ is obtained in a non-stoichiometric ratio by the double-crucible method, and it shows similar luminescent properties as the single particle. Upon excitation with violet light (400 nm), the maximum emission wavelength of the as-prepared Ba5(1-x)Si11Al7N25: 5xEu2+ phosphors shift from 558 nm to 591 nm with Eu2+ ions concentration increasing, and the full width at half-maximum (FWHM) increase from 87 nm to 100 nm. The broad emission band is attributed to three luminescent centers corresponding to three different Ba2+ ions sites Ba5Si11Al7N25:Eu2+ phosphor, which is demonstrated by time-resolved emission spectra and the decomposition of the emission spectrum at 4 K. The Ba5Si11Al7N25:Eu2+ phosphor shows a small thermal quenching with a quenching temperature as high as 700 K. The as-prepared phosphor can absorb both of UV and blue light effectively and exhibits similar quantum efficiency under the excitation of 400 nm (58.5 %) and 450 nm (54.5 %). The fabricated white LED lamp emitted a warm white light with CIE coordinates of (0.3838, 0.3252) and CCT = 3412 K, implying the potential applications in warm w-LEDs.

Structural and optical studies on Dy3+ doped Gd2Ti2O7 pyrochlore as white light emission

A series of Dy3+ trivalent ion embedded into the GTO pyrochlore (Gd2-xDyxTi2O7 (x = 0.5, 1.0, 1.5, 2.0, and 2.5 mol%)) have been synthesized through standard solid state reaction technique. The single phasic nature with Fd3m space group was determined through XRD, Raman spectroscopy, and photoluminescence spectroscopy. Rietveld refinement analysis results confirm that the substitution is not going to disturb the crystallographic structure as well unit cell dimensions. From Raman deconvoluted spectrums, it was found that all the vibrational bands show a very small blue shifting on Dy3+ substitution. The photoluminescent EM-spectra for all the samples were examined under the excitation wavelength 347 nm gives two high intense emission bands centered around 484 nm (blue) and 581 nm (yellow) due to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions respectively, and less intense band appeared at wavelength of 456 nm arising due to the 4I13/2 → 6H13/2 transition of Dy3+ ions. For the optimum Dy3+ concentration (2.0 mol%), the Y/B ratio is found to be 0.8753 which is close to unity hence combination of both yellow and blue emission bands emits white light as validated by CIE chromaticity coordinates calculated values are (x = 0.34959, y = 0.35381). Therefore, the results reveal that Dy3+ substituted GTO pyrochlore samples could be used as luminescent material for wLEDs application.

Controlled synthesis of GaN square shape nanorods: Their excellent electronic and optical properties for optoelectronics applications

High quality square shaped GaN nano-rods are successfully synthesized by a novel method of precursors pretreatment with aqueous NH3 via CVD method at 1300 °C. The pre-treatment effect significantly enhanced the conductivities, carrier concentrations and mobilities in GaN nanorods. GaN nanowires have also been synthesized at 1300 °C without treating precursors with aqueous NH3. Diameter of the nanorods and nanowires are measured in the range of 100-200 nm whereas length is in tenth of microns. Room temperature PL analysis of GaN nanowires displayed a high intensity near-band-edge emission at 370 nm with week blue emission. The GaN square nanorods exhibited the yellow band emission at 565 nm vanishing the weak blue emission along with the near-band-edge emission at 369 nm indicating their potential applications in optoelectronics. The carrier concentrations (Nd) are calculated to be 3.65–5.25 × 1016 cm−3 and 2.25∼5.88 × 1018 cm−3 for nanowires and nanorods respectively. The electron mobilities (μ) calculated for the GaN nanowires were in the range of 200∼300 cm2/Vs where as for the nanorods were 154∼625 cm2/Vs. The high quality GaN nanorods building blocks with high conductivities, career densities and mobilities will be a tremendous breakthrough in low voltage operating nano-devices.

Influence of the nature of defects in ZnO nanocrystals synthesized by chemical bath deposition on photocatalytic activity

We investigated the influence of various native defects in ZnO nanocrystals with homogeneous morphological properties on the structural, optical and photocatalytic characteristics of ZnO nanocrystals. In the photoluminescence spectrum of as-grown ZnO nanocrystals, a yellow emission band (YB) was observed, corresponding to interstitial oxygen (volume defect). When the ZnO nanocrystals were annealed at 200 °C, this YB disappeared and the NBE emission intensity increased. When ZnO nanocrystals were annealed at a temperature of 500°С, a green emission band appeared in the photoluminescence spectrum. This emission band belongs to oxygen vacancies, and this defect is located in the surface or subsurface of the nanostructure (surface defect). Studies have shown that the photocatalytic properties of ZnO nanocrystals depend on the nature of the native defects, and the increase in the concentration of defects and the appearance of surface defects lead to an increase in the photocatalytic activity of the sample.

Analysis of blue (BE), green (GE), yellow (YE), and red (RE) emission band in ZnO quantum dots

ZnO quantum dots (QDs) are prepared by the green technique of colloidal synthesis. Structural, morphological, and optical properties of ZnO (QDs) were investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Photoluminescence. They were prepared ZnO (QDs) in different crystalline growth temperature ranges ∼60–210 ± 4 °C. Using the Hall-effect, we can measure the concentration of carriers, electronic mobility, and resistivity. The morphology and grain size distribution of ZnO (QDs) were analyzed by SEM. Through XRD studies, the hexagonal phase is identified and the grain size was estimated from Scherer’s method, situated at a range of ∼4.2–6.3 nm. Optical properties were investigated by UV-Vis spectroscopy. In Transmittance ( %T) studies, ZnO (QDs) reached ∼80 %, as well as a relative maximum shift at a range of ∼402–378 nm (∼3.08–3.28 eV). The Normalized Absorbance shows different relative maxima at UV-Vis, associated with VB→CB electronic transition and electronic intra-transitions assigned to intrinsic native crystalline defects located at ∼500–700 nm (∼2.48–1.77 eV), shows that the absorption bands originating from the F0 centers prevail over those of F+0 centers of VO when the intrinsic native crystalline defect concentration is high. The Tauc model was used to determine the optical gap energy of ZnO (QDs) is located at ∼3.08–3.26 eV, an optical phenomenon associated with quantum confinement. Photoluminscence (PL). PL signals show emission bands with different intensities: blue (YB), green (GE), yellow (YE), and red (RE) bands, situated in the Vis-region, and commonly associated with color points produced by vacancies and interstices crystalline. Interface passivation layer deposited onto photo anodes has been proven to be an available way to suppress charge recombination and enhance the power conversion efficiency in quantum dot-sensitized solar cells.

Temperature Control of Yellow Photoluminescence from SiO2-Coated ZnO Nanocrystals.

In this study, we aimed to elucidate the effects of temperature on the photoluminescence from ZnO–SiO2 nanocomposite and to describe the preparation of SiO2-coated ZnO nanocrystals using a chemical precipitation method, as confirmed by Fourier transform infrared (FTIR) and powder X-ray diffraction analysis (XRD) techniques. Analyses using high-resolution transmission microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), and electrophoretic light scattering (ELS) techniques showed that the new nanocomposite has an average size of 70 nm and 90% silica. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and photoluminescence-excitation (PLE) measurements at different temperatures revealed two emission bands at 385 and 590 nm when the nanomaterials were excited at 325 nm. The UV and yellow emission bands were attributed to the radiative recombination and surface defects. The variable-temperature, time-resolved photoluminescence (VT-TRPL) measurements in the presence of SiO2 revealed the increase in the exciton lifetime values and the interplay of the thermally induced nonradiative recombination transfer of the excited-state population of the yellow emission via deep centers (DC). The results pave the way for more applications in photocatalysis and biomedical technology.

Facile one-pot preparation and luminescence mechanism of stable Bi3+-doped Cs2AgInCl6 double perovskite nanocrystals

Lead-free alloyed Cs2AgInCl6 nanocrystals (NCs) are currently considered as a new class of lead halide perovskite alternative due to their less toxicity and excellent intrinsic stability. However, their solution preparation process with oleylamine as ligands are easy to the formation of metallic Ag due to the reduction of Ag+, resulting in poor photoluminescence (PL) performance of NCs. Herein, a facile one-pot solution synthesis strategy was proposed to prepare stable Bi3+ doped Cs2AgInCl6 NCs via tri-n-octylphosphine (TOP) as co-ligands, and the emission mechanism was further investigated. The prepared Bi3+ doped Cs2AgInCl6 NCs show broad dual emission bands at around 410 nm and 565 nm, in which the violet emission band is ascribed to the surface defect states, while the yellow emission band of as-synthesized NCs is attributed to the 3P1→1S0 self-trapped excitons recombination of Bi3+ ions. Due to the introduction of BiCl6 states after doping with Bi3+ and well elimination of surface metallic silver by strongly coordinating of TOP, the PL quantum yield of as-synthesized NCs is obviously elevated from 1.25% to 5.10%. The prepared Bi3+ doped Cs2AgInCl6 NCs exhibit excellent storage stability and light stability, making it a promising single emitter fluorescence material for white light-emitting diode devices.

Study on energy transfer mechanism and optical properties of LiLaSiO4: Dy3+, Tb3+ phosphors with excellent thermal stability and color tunability

In this paper, a variety of color-tunable LiLaSiO4: xDy3+, yTb3+ phosphors were manufactured by high temperature solid phase method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and Photoluminescence (PL) were used to characterize the phase, luminescence properties and thermal stability of the samples. In LiLaSiO4: Dy3+ phosphors, the best doping concentration is x = 0.03, corresponding to the pale yellow emission band. In LiLaSiO4: Dy3+, yTb3+ (y = 0–0.06) phosphors, energy transfer can be verified and the energy transfer mechanism are discussed in detail. In addition, by adjusting the concentration ratio of Dy3+/Tb3+ in LiLaSiO4 phosphors, the color tuning from pale yellow to green was realized. Finally, we also study its thermal stability, the activation energy (ΔE) is −0.1483 eV. Current research shows that Dy3+, Tb3+ co-doped LiLaSiO4 phosphors have wide application potential in fluorescent display devices.