White Luminescence Research Articles

The Role of Ce3+ Co-doping in the Luminescent Enhancement of Bi3+ Emission and Bi3+→Bi2+ Conversion in LiLaP4O12 Host

This work investigates the luminescent versatility of the LiLa(1-x-y)BixCeyP4O12 system as a scintillator material capable of displaying emission in a range from the blue to the red region depending on the Ce3+ concentration. The LiLaP4O12 host has been proven to be useful as a scintillator material when doped with some rare earths and with bismuth ions. However, the process of bismuth valence change induced by X-rays, when inserted in the LiLaP4O12 matrix, is not known to date, as well as whether this can be controlled and used to enhance the luminescence emission. To determine the mechanism of interaction between the Ce3+ and Bi3+ ions in the LiLaP4O12 host, doped and co-doped samples were synthesized and investigated. Identification of crystalline phase was carried out with X-Ray Powder Diffraction. The luminescent properties were studied via photoluminescence emission and excitation using synchrotron radiation. Scintillator features were studied through radioluminescence emission spectrum. The results indicate that Ce3+ transfers either energy or electrons to Bi3+ when excited with UV (5.2 eV) or X-rays, respectively. In the first case, the overall white luminescence is improved, while in the latter, enhanced red luminescence from Bi2+ was observed, indicating the valence change of Bi ions, assisted by Ce co-dopant. A luminescent mechanism, based on the vacuum-referred binding energy model applied to the experimental data, was proposed to explain the Bi2+ emission, deepening the understanding of the Bi emission mechanism and opening the possibility of tailoring the Bi2+/Bi3+ proportion varying the Ce-co-doping concentration.

Heterostructure of Hydrogen‐Bonded Organic Frameworks for White Light Emission and Information Encryption

AbstractTwo dumbbell‐shaped building blocks (TMB and TMBT), featuring methyl benzoate groups as hydrogen bond units, are selected to construct heterostructures of HOFs, aiming to achieve multiple functions including white luminescence, stimulus‐response behavior, as well as application in information encryption. TMB molecules are self‐assembled to form a flexible HOF (X‐HOF‐8) in p‐xylene, containing solvent channels and blue fluorescence. Upon removal of guests, it can transform into a nonporous crystal with gray fluorescence. In contrast, TMBT forms a guest‐free HOF (X‐HOF‐9) displaying orange fluorescence. They could form bulk heterojunction (BHJ) HOFs with energy transfer from TMB to TMBT, exhibiting composition‐dependent fluorescent color. Notably, white emission can be achieved in BHJ HOFs and can be converted to gray fluorescence upon guest removal; subsequently, white fluorescence is restored upon re‐capturing guests. Furthermore, rod‐like triblock heterojunction (THJ) HOFs can also be constructed, which exhibit regulatory behavior in response to gaining or losing guests. The unique luminescent characteristics and stimulus responsiveness of these HOFs make them an excellent platform for applications in anticounterfeit. This represents the pioneering achievement of white light emission in a BHJ HOF, as well as the groundbreaking realization of a THJ HOF with remarkable exciting response characteristics.

White afterglow achieved in Eu2+, Ce3+, Dy3+co-doped LiSr4(BO3)3 phosphor

In prior study by our team, orange-yellow afterglow was observed in Eu2+ and Dy3+ co-doped LiSr4(BO3 )3 phosphor due to the emission from Eu2+ center. In this study, further incorporation of Ce3+into the phosphor lead to the observation of white afterglow due to the mixed result of blue light from Ce3+ and orange-yellow light from Eu2+ centers. Upon ultraviolet excitation, the phosphor displays a spectrum characterized from blue emission of Ce3+ at 462nm and orange-yellow emission of Eu2+ at 632nm. Fine-tuning the concentration of Ce3+ enabled the realization of white luminescence in LiSr4(BO3)3: Eu2+, Ce3+ and Dy3+phosphor with chromaticity coordinates of (0.3979, 0.2939). The photoluminescence intensities of the samples could be modulated by incorporating varying amounts of Ce3+ ions, with a critical quenching concentration identified with 0.16 Ce3+. White afterglow is also observed after the removal of the light illumination due to the existence of suitable electron traps with optimal trap depth created by the co-doped Dy3+. The underlying mechanism proposes that the white afterglow is generated by the mixed lights of blue and orange-yellow that are created by the recombination of heat-released electrons from the trap centers with pre-existing holes in the Ce and Eu emission sites.

A Single‐Component Sb/Ho: Cs2Na0.9Ag0.1(In/Bi)Cl6 White Phosphor with a Record Color Rendering Index of 97.4

AbstractThe study on phosphors‐converted white light‐emitting diodes (pc‐WLEDs) using lead‐free double perovskites (DPs) as single‐component white phosphors is widely concerned. However, the photoluminescence quantum yields (PLQY) of white luminescence and color rendering index (CRI) of WLED are not satisfactory. Herein, a new Sb/Ho: Cs2Na0.9Ag0.1(In/Bi)Cl6 single‐component white phosphor with the highest PLQY of 93% and a record CRI of 97.4 is reported. Experimental data and theoretical calculations evidence that in addition to broadband yellow emission of the self‐trapped exciton (STE) recombination, the material also exhibits blue emission from Sb3+: 3P1→1S0 transition and red one assigned to Ho3+: 5F5→5I8 transition. Steady‐state and time‐resolved PL spectra verify the existence of two energy transfer channels from both Sb3+ and STE to Ho3+ dopants. As a demo, Sb/Ho: Cs2Na0.9Ag0.1(In/Bi) Cl6‐based WLED is constructed, showing excellent comprehensive optical performance with specially improved saturation red index R9 and blue one R12. This work provides a novel single‐component rare‐earth doped DP white phosphor for high CRI full‐spectrum solid‐state lighting.

Luminescence and spectroscopic studies on Dy3+-Eu3+ doped SiO2-B2O3-ZnO-La2O3-BaO glass for WLED

A series of SiO2-B2O3-ZnO-La2O3-BaO (SBZLBa) glasses doped with Dy3+ and Eu3+ were synthesized using the melt-quenching technique. Their optical characteristics and potential applications in W-LED devices were investigated. The structural effects resulting from doping the glass with Dy3+ and Eu3+ ions were elucidated through infrared spectroscopy and an examination of the physical properties. The variations in emission intensity within the fluorescence spectrum validated the sensitizing effect of Dy3+ on Eu3+ within the glass matrix. By manipulating the transitions of both Dy3+ and Eu3+, the excitation wavelength was altered, enabling the realization of cool white, neutral white, and warm white luminescence, thus accommodating the diverse requirements for white light emission in lighting applications. After incorporating 1.0 mol% of Dy2O3 and 0.8 mol% of Eu2O3, respectively, the glass exhibited CIE coordinates of (0.3332, 0.3535), positioning it within the white light spectrum and in close proximity to the ideal white light coordinates of (0.33, 0.33). The SBZLBa-Dy2O3–0.8Eu2O3 glass exhibited a quantum yield of 5.98 %. It has been demonstrated through acid and alkali resistance tests that this glass possesses excellent chemical stability. Additionally, temperature-dependent emission spectra have revealed that the luminous intensity of the glass maintains over 85 % of its room temperature value at 185 °C, with Eα determined to be 0.2387 eV.

Fabricating of turquoise/white luminescent azo-Schiff bases bearing benzimidazole and imidazole rings

New azo dyes (1a-b) were prepared by the azo coupling reaction of 2-nitro-1,4-phenylenediamine with 5-chlorosalicylaldehyde and 5-chloro-2-hydroxyaniline. Corresponding Schiff base derivatives (2a-b) bearing conjugated benzimidazole and imidazole moieties were obtained via the condensation reaction of these dyes with 2-aminobenzimidazole and 4-imidazolecarboxaldehyde. Their structures were characterized by elemental analysis, FT–IR, 1H/13C NMR, LC-MS and UV–Vis spectroscopic techniques. Chromic (solvato-, acido-, thermo-) and photoluminescence behaviour of compounds 2a and 2b were evaluated depending on their donor–π–acceptor molecular system and intramolecular proton tautomerism. The absorption and emission spectra of 2a and 2b were recorded in DMSO, DMF and CHCl3. 2a emitted turquoise luminescence in DMSO and DMF, and white luminescence in CHCl3, while 2b emitted strong turquoise luminescence in only CHCl3.

Effect of Mn2+ Doping on the Photoluminescence of Hybrid One-Dimensional Lead Halide Post-Perovskites.

Although organic-inorganic hybrid one-dimensional (1D) lead halide postperovskites (LHPPs) have been reported to show white luminescence and tunable photoluminescence quantum yield (PLQY), their structure-property relationships are not fully understood. Here, we used Mn2+ to test the doping effect on the luminescence of two 1D-LHPPs compounds, namely, {TETA[Pb2Br6]}n 1 and {TETA[Pb2Cl6]}n 2, where TETA = triethylenetetrammonium. We found the pristine compounds show yellowish (551 nm) and bluish (447 nm) emission for 1 and 2, respectively, nanosecond excitation lifetimes (4.17 ns for 1 and 2.29 ns for 2) and low PLQYs (4.65 and 3.57% for 1 and 2, respectively). By fine-doping the Mn2+ ions to ca. 8% the PLQYs for 1 and 2 are maximized to 24 and 25% for 1 and 2, respectively. Upon the increasing Mn2+ dopant, the emission wavelengths can also vary gradually from 551 to 615 nm and from 447 to 660 nm for 1 and 2, respectively, covering almost the whole visible-light range, and the excitation lifetimes are enhanced to microseconds (0.77 μs for 1 and 0.39 μs for 2), owing to the more spin-forbidden d-d transition (4T1-6A1) component from the Mn2+ ions present in the photoluminescence spectra. Moreover, these Mn2+-doped 1D-LHPPs demonstrate high structural and optical stability in humid and high-temperature environments. Hence, such doped materials can be fabricated into a UV-pumped white light-emitting diode, rendering the potential application for solid-state lighting and display systems.

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.

Surfactant-Assisted Förster Resonance Energy Transfer from a Quantum Dot Complex for Highly Stable White Light Emission.

Herein we report the fabrication of a surfactant modified quantum dot complex (S-QDC, having λem = 485 nm) nanocomposite (composed of cetyltrimethylammonium bromide surfactants and a zinc-quinolate complex attached ZnS quantum dot), the donor capability of S-QDC in Förster resonance energy transfer (FRET) with an acceptor organic molecule (λem = 573 nm), and finally their utilization in the FRET-based white light emission having features near to mid-day sunlight. The Förster distance, energy transfer efficiency, donor-acceptor distance, number of binding sites, and binding constant are evaluated to be 3.48 nm, 85.74%, 2.58 nm, 0.94, and 1.87 × 104 M-1, respectively, for the current electrostatically driven FRET pair. The solid polymer coated FRET pair composite emits white light having chromaticity color coordinates of (0.33, 0.33) and correlated color temperature of 5350 K and also shows long-term atmospheric white luminescence stability up to 30 days, photostability, and thermal stability with preservation of their pristine morphology.

Simultaneous modification of emission spectrum and trap distribution for achieving self-trapped excitons-based white afterglow

The incommensurable differences between the feeding and actual doping ratios of luminescent dopants and excessive reliance on rare-earth ions become two key problems in halide perovskite-based afterglow materials, restricting the production cost and further application. Here, we prepare a series of novel lead- and rare-earth-free halide afterglow phosphors Cs2(Na0.9Ag0.1In)1-xZrxCl6 under an ambient condition, in which the Zr dopants modify the lattice thus tailoring the emission spectrum and trap distribution, simultaneously. The focused Cs2(Na0.9Ag0.1In)0.6Zr0.4Cl6 with mainly size distribution of ∼ 0.6–1.8 μm exhibits ∼ 350–850 nm ultrabroad white luminescence under ultra-violet excitation, and the introduced traps endow the white emission with a long-persistence of over 5 h after pre-irradiation. The absorption bands of self-trapped excitons (STEs) are observed in the steady-state absorption spectra during the afterglow process, suggesting the general accepted picosecond-scaled lifetimes of STEs have been successfully prolonged to hour-scale, which provide a potential opportunity for investigating the specific behavior of STEs.

Cooperative sensitization upconversion of ex-situ sol-gel synthesized ZnO-SiO2: Nd3+/Yb3+ dense glass ceramic material under 980nm laser pumping

Herein, we use a modified ex-situ sol-gel synthesis route to prepare Zinc-Silicate (ZnO-SiO2:Nd3+/Yb3+) dense glass ceramic material. The Judd-Ofelt parameters were estimated from absorption spectra of the ZnO-SiO2:Nd3+/Yb3+ material. Upconversion luminescence (UCL) in the material was achieved due to the sensitization of Yb3+ ions through 980 nm diode laser excitation along with CIE 1931 chromaticity diagram to analyze the white light emission. PL confocal microscopy was used to confirm the spatially resolved PL of the material. Thus, the as-synthesized material demonstrates its viability by producing white luminescence across its surface when excited by a 980 nm diode laser, which could find potential applications in various photonic applications. TEM-EDS mapping of material was performed to visualize elemental doping of the material. The structural characterization of the material was studied with X-ray diffraction (XRD) analysis and FTIR spectroscopy to report invariance of ZnO-SiO2 host. The thorough removal of hydroxyl impurity (-OH) and the pyrolysis of zinc alkoxides were confirmed through thermogravimetric (TG) and differential scanning calorimetry (DSC) analysis.

Effect of annealing temperature on Eu2+ and Eu3+ ratios in AlN:Eu thin films

Eu-doped aluminum nitride (AlN:Eu) thin films were fabricated and characterized in a way of white light generation. AlN exhibits blue luminescence originating from defect levels. Furthermore, Eu2+ demonstrates green luminescence, while Eu3+ emits red light. Consequently, white luminescence is anticipated in Eu-doped AIN thin films. The concept is to control the ratio of Eu2+/Eu3+ in the thin film to vary the emission colors. We aimed to manipulate the Eu valence ratio in AIN:Eu thin films by changing the annealing temperature and examining the resultant luminescence characteristics. Our findings revealed an increase in defect-related luminescence in AIN samples annealed at higher temperatures, along with a rise in the Eu2+ fraction. We explore these outcomes in relation to the structural models surrounding Al and Eu ions, as elaborated in the main text.

Multicolor regulation of trivalent lanthanide ions-codoped boggildite-type phosphor toward superb warm white luminescence for white light-emitting diodes

Mineral-inspired single-component phosphors with multicolor-emitting feature are desirable for illumination-grade solid-state lighting applications. However, it remains challenging in phosphors to directly achieve the warm white-light modulation via the intrinsic f–f transitions from trivalent lanthanide cations. Herein, substantially regulatable multicolor luminescence is realized in the single-component boggildite-type (Na2Sr2Al2(PO4)F9) phosphors. The warm white-emitting phosphor Na2Sr2Al2(PO4)F9:0.07 Tb3+, 0.05Eu3+ was firstly obtained, and it possesses multiple emission bands distributing in the entire visible spectral region and exhibits desirable thermal stability (86.2%@423 K of the integrated fluorescence intensity at 298 K) and high internal quantum efficiency (83.8%), overwhelming other currently representative single-component white-emitting phosphors. Multicolor emission evolution in large color gamut covering the warm white region was reached via fine regulating Tb3+/Eu3+ dopant ratio in Na2Sr2Al2(PO4)F9:0.07 Tb3+, zEu3+ (z = 0–0.10) phosphors contingent on their energy transfer between Tb3+ and Eu3+, theoretically verified by the Kushida–Malta model. A fabricated white light-emitting diode prototype coated with the composition-optimized Na2Sr2Al2(PO4)F9:0.07 Tb3+, 0.05Eu3+ phosphor finally provided ideal warm white light output with color rendering index and correlated color temperature of 88.7 and 3384 K, as well as favorable luminous efficacy of 62.4 lm/W, demonstrating its significant potential for industrial applications in illumination-grade warm white light-emitting diode devices. Guided by the known mineral-type structural prototypes, the present study demonstrates a unique approach to realizing the unexpected warm white emission in novel mineral-type phosphor system by only doping trivalent lanthanide ions to achieve the excellent luminescence performance for solid-state lighting applications.

Direct white light luminescence from Ho3+/Pr3+ co-doped fluoride fiber with blue diode pumping

White light luminescence induced by a blue diode laser was investigated in a double-clad Ho3+/Pr3+ co-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber. The pump laser at 442 nm can simultaneously excite Ho3+ and Pr3+ ions, resulting in synergistic luminescence. The emission spectra include multiple visible bands in the blue, green, orange, red, and deep-red spectral regions, which correspond to the 4f-4f electronic transitions of Ho3+ and Pr3+ ions. The relative intensity of emission bands is dependent on the pump power, and the CIE 1931 chromaticity diagram illustrates the dependence of color tunability on the pump power. Under laser excitation at 442 nm, the CIE coordinates are within the white light range, and the CCT values are between 6900 and 8700 K. The results indicate that double-clad Ho3+/Pr3+ co-doped ZBLAN fibers that are directly blue diode-pumped have the potential to be used in high-power white light fiber lasers.

Structural and optical properties of silicon oxycarbide thin films using silane based precursors via sol-gel process

Silicon oxycarbide (SiCxOy) is a candidate material for white luminescence. This work investigates the formation of SiCxOy thin film coating by sol-gel route using various silanes namely, methyltrimethoxy silane (MTMS) with or without using tetraethyl orthosilicate, vinyltrimethoxysilane and polydimethyl siloxane, followed by calcination at 1000 °C/1 h under Ar atmosphere. The structural and optical properties of the developed films were studied by X-ray diffractomete (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), electron paramagnetic resonance (EPR) spectroscopy and Photoluminescence (PL). XRD plot shows amorphous nature of silicon oxycarbide (SiCxOy) while FTIR reveals Si-C band at 795 cm−1 and Si-O-Si band at 1085 cm−1 confirming the presence of SiCxOy. XPS analysis of MTMS derived coating revealed stoichiometry of SiC0.3O2.25 which is comparable to SiCxOy (0.2<x<0.6, y<1.6). EPR spectra analysis shows presence of Si-dangling bond which could be the probable cause of luminescence center in SiCxOy as observed from PL study. FESEM shows uniform coating of thickness ∼200 nm. PL spectra shows blue and green emission peaks at ∼ 403–452 and ∼ 483–560 nm, respectively.

Utilizing weakly donor-acceptor ternary π-conjugated architecture to achieve single-component white luminescence and stimulus-responsive room-temperature phosphorescence.

Purely organic room-temperature phosphorescence (RTP) has garnered substantial attention for its delayed emission, environmental sensitivity, and potential diverse applications. However, the quest for high-performance RTP materials has always been a challenge. In this study, we introduce novel weakly donor-acceptor (D-A) ternary π-conjugated architecture to construct an efficient RTP system. The strategy utilizes synergistic effects of the analogous El-Sayed rule, halogen-free heavy-atom effect, reduction of the singlet-triplet energy gap, and manipulation of flexible molecular conformation. A remarkable enhancement in the phosphorescence-to-fluorescence ratio was achieved, elevating from 0.4 in carbazole to 35.2 in DBTDBTCZ. Furthermore, the RTP system demonstrates single-component white luminescence, yielding warm and cool white colors. Intriguingly, we unveil the novel position-dependent heavy-atom effects, discerningly promoting intersystem crossing or phosphorescence decay. Benefiting from efficient RTP, multifunctional applications of real-time humidity monitoring, oxygen sensing, anti-counterfeiting labeling, and white lighting are demonstrated.

Fluorescence properties of novel deep-red phosphor LiMg4SbO7:Mn4+ with excellent quantum efficiency and color purity for warm white LEDs.

Red fluorescent materials have important application value in the background light and LED lighting fields of displays. In this work, a novel type of rare earth free deep-red phosphor LiMg4SbO7:Mn4+ was prepared successfully, and its crystal structure, microstructure, fluorescence spectrum, quantum yield, thermal stability, fluorescence lifetime, color coordinates and color purity were studied in detail. The excitation spectra of LiMg4SbO7:Mn4+ phosphors are located at 200-600 nm, which can be matched with ultraviolet, near-ultraviolet, and blue-light chips. The exciting result is that the LiMg4SbO7:0.002Mn4+ phosphor exhibits astonishing quantum efficiency, thermal stability and color purity. Finally, the developed LiMg4SbO7:Mn4+ and the yellow phosphor Y3Al5O12:Ce3+ (YAG:Ce3+) were mixed and coated on a blue light chip (460 nm) to produce a w-LED, which exhibited warm white luminescence with color coordinates of (0.3575, 0.3809), correlated colour temperature (CCT) of 4687 K, and color rendering index (CRI) of 83.6. It is reasonable to consider that LiMg4SbO7:Mn4+ phosphors with excellent photoluminescence performance have great application value in LED lighting fields.

Green synthesis of Zinc Oxide nanoparticles, antibacterial studies and investigation as catalyst for the conversion of pumpkin oil into biodiesel

Zinc oxide nanoparticles were synthesized by employing solution combustion method using environmental friendly Cellophyllum innophyllum seed powder as fuel. Phase purity, crystallite size were determined from X-ray diffraction (XRD). Organic species attached to the surface of the nanoparticle were identified using Fourier transform infrared spectroscopy (FTIR). Morphological studies were performed using TEM and SEM. Bandgap increased with decreasing particle size as confirmed from the diffuse reflectance spectroscopy (DRS) white light luminescence capabilities of ZnO NPs were studied using photoluminescence spectroscopy. In vitro antibacterial activity studies and catalytic property for the conversion of pumpkin seed oil into biodiesel were performed.

The Growth Mechanism, Luminescence, and Lasing of Polyhedral ZnO Microcrystals with Whispering-Gallery Modes

This work studies the features of the formation of isometric polyhedral ZnO microcrystals that provide stimulated emission and whispering-gallery-mode (WGM) lasing in the near-UV range. For this purpose, the growth stages of such crystals in the process of gas-transport synthesis and the luminescent properties of the structures obtained at each stage were investigated. It was shown that the growth of laser microcrystals begins with the formation of microspheroids with thin ZnO shells. Such spheroids exhibit mainly white luminescence with a small contribution of near-UV emission. Increasing the synthesis duration results in thickening and faceting of the spheroid shells, as well as a decrease in the contribution of the yellow–red component to the luminescence spectrum. At the same time, ZnO microcrystallites nucleate and grow inside the spheroids, using as a material the remains of a liquid zinc drop and oxygen entering the spheroids through their shells. Such growth conditions allow them to take on an equilibrium polyhedral shape. Eventually, upon destruction of the spheroid shell, a polyhedral ZnO microcrystal supporting WGMs is observed.

Tunable Emission and Energy Transfer of the Novel KY1−x(MoO4)2−y(WO4)y:xLn3+ (Ln3+ = Dy3+, Eu3+, and Tm3+) Single-phase White Luminescence Phosphor for White LEDs

Tunable Emission and Energy Transfer of the Novel KY1−x(MoO4)2−y(WO4)y:xLn3+ (Ln3+ = Dy3+, Eu3+, and Tm3+) Single-phase White Luminescence Phosphor for White LEDs