Intense White Light Emission Research Articles

Intense white-light emission of amorphous lead chloride trimers at high pressure.

Developing efficient, single-phase white-light phosphors remains a formidable challenge in optoelectronics. Herein, high pressure initially induces trimeric contraction and distortion in (C9NH20)9(ZnCl4)2[Pb3Cl11], regulating the transition equilibrium of self-trapped excitons (STEs) with varied emission colors. Then, considerable structural distortion and destruction lead to intense white-light emission of an amorphous phase. A narrowed bandgap with promoted excitation efficiency, as well as strengthened electron-phonon coupling effect with increased binding energy of STEs, together result in the significant emission enhancement. This work provides valuable insights into white-light luminescent materials and offers new strategies for designing white-light-emitting devices.

Study on structural luminescence characteristics of a new Dy3+ activated white luminescent phosphor

A series of Y1-xGa1.5Al1.5(BO3)4: xDy3+ were prepared by a high-temperature solid-phase method. Rietveld refinement characterized the phase purity of the samples obtained, suggesting that the prepared phosphors were high-purity material phases. After synthesizing high purity phase, the luminescence mechanism is revealed, under 348 nm excitation in Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the samples have two characteristic peaks at 480 nm and 572 nm and the burst mechanism is dipole-dipole mechanism. The mechanism of luminescence and quenching is analyzed by analyzing the band structure, and the relationship between the band gap and thermal stability is explained. The prepared phosphor has a quantum efficiency of 51.22 % and exhibits intense white light emission. The thermal stability of the samples was characterized, and the phosphor could still achieve 88.20 % thermal stability at 423 K. Finally, the chromaticity coordinates of the Y1-xGa1.5Al1.5(BO3)4: xDy3+ phosphors all fall in the white-light region, with the color coordinates around (0.33, 0.33). By combining with the 365 nm chip and Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor, the W-led device with Ra = 68.3 and CCT = 6670 K was synthesized. Therefore, the Y0.97Ga1.5Al1.5(BO3)4: 0.03Dy3+ phosphor prepared in this experiment has some application value in the field of solid-state lighting.

Deciphering the Role of Gamma Ray Induced Radicals in the Thermoluminescence Process of a Neutral to Cool Daylight Emitting Sr1–xB4O7–Dyx Phosphor through Electron Paramagnetic Resonance (EPR) Spectroscopy

A number of researchers have reported on the thermoluminescence (TSL) properties of many borates activated with rare earths and transition metal ions. However, there are not many reports that pinpoint the role and chemical nature of the gamma induced radicals. Further, there are even fewer reports highlighting the multifunctional characteristics of a single TSL phosphor. In this work, we showcase SrB4O7 doped with Dy3+ for the dual role of white light emitting as well as a TSL dosimetric material. We did the PL/TSL/EPR (electron paramagnetic resonance) correlation studies in order to identify the active luminescent centers, the trap parameters and the chemical nature of the radicals responsible for the phenomena. By doing a systematic study on a series of Dy3+ (1–10 mol %) doped samples, we optimized the composition. Colorimetric studies on the optimized sample revealed that it had intense near white light emission with 38.1% color purity when excited by UV-C light (247 nm). The same sample also showed a linear gamma dose response up to 1600 Gy (J/kg). A detailed EPR investigation confirmed the role of a borate based radical in the observed TSL process. We believe that the material can be a good candidate for real life application as a multifunctional material.

Tuning the Red Emission to Instigate Intrinsic White-Light Emission in Single-Phase Phosphor with Excellent Color Rendering Index.

There is ever-growing interest to develop intrinsic white light emitting single-phase phosphors that have high CRI, devoid of bluish tinge, ease of synthesis and are scalable. Herein, manipulating vacuum pressure to instigate white light emission in Cu2+ -doped-ZnS phosphors is reported. The detailed X-ray diffraction and electron microscopy confirm the cubic phase of Cu2+ -doped-ZnS phosphor having agglomerated particles (∼130-150 nm). The incorporation of Cu2+ in the ZnS lattice is substantiated by the anti-Stokes shift of Raman peaks and shifting of XRD peaks to higher 2θ values. Upon increasing Cu2+ doping concentration, the resulted decrease in the FWHM of XRD peaks implies shrinkage of the ZnS lattice. Interestingly, by tailoring the excitation wavelength, the stoichiometry of dopant ion, and defect states by varying the vacuum pressure, the optimized ZSC-3 (3% Cu2+ -doped-ZnS) displays the origin of clear blue, green and red emission bands, consequently giving rise to white light emission (CIE values: 0.345:0398). The PLQY and average lifetime calculated for ZSC-3 are 5.98% and 1.5 ms, respectively. Such intense white light emission prompted to fabricate a prototype using a 310 nm UV LED. It exhibits high CRI (97) and warm CCT (4538 K), meeting highly desired values for a white light-emitting phosphor for different lighting and electroluminescence applications.

Coupling Intracompound Charge Transfer and Cluster‐Centered Excited States in Cu(I) Halide Hybrids for Efficient White Light Emission

Abstract0D hybrid organic–inorganic metal halides have attracted significant interest due to their unique optoelectronic properties, but attainment of efficient and stable white light emission (WLE) in such compounds remains a challenge. Here, efficient WLE via a molecular design that couples intracompound charge transfer and cluster‐centered excited states in 0D halide hybrids is demonstrated. Two Cu(I) halide hybrids, K(18‐crown‐6)Cu2Br3 and Na4(18‐crown‐6)5In2Cu4Br14·8H2O, are synthesized wherein luminescent [Cu4Br6]2− clusters are isolated from each other and surrounded by 18‐crown‐6 coordinated alkali metal cations. In the case of K(18‐crown‐6)Cu2Br3, [Cu4Br6]2− clusters are only partially isolated, leading to strong orange emission with a photoluminescence quantum yield (PLQY) of 53% under UV excitation. Strikingly, to a larger extent of isolation as that, in Na4(18‐crown‐6)5In2Cu4Br14·8H2O as a result of the incorporation of nonemissive [InBr4]− clusters, intense white light emission with a PLQY of 97% is achieved. The dual cluster‐centered states, coupled with a mixed metal‐to‐ligand and halide‐to‐ligand charge transfer state, are responsible for this bright white luminescence. This work provides new design principles for expanding the materials library for single‐component, solid‐state WLE.

Laser-Induced Generation of Hydrogen in Water by Using Graphene Target.

A new method of hydrogen generation from water, by irradiation with CW infrared laser diode of graphene scaffold immersed in solution, is reported. Hydrogen production was extremely efficient upon admixing NaCl into water. The efficiency of hydrogen production increased exponentially with laser power. It was shown that hydrogen production was highly efficient when the intense white light emission induced by laser irradiation of graphene foam was occurring. The mechanism of laser-induced dissociation of water is discussed. It was found that hydrogen production was extremely high, at about 80%, and assisted by a small emission of O2, CO and CO2 gases.

Determination of spectroscopic parameters and thermoluminescence studies of Dy3+-activated Ba2ZnSi2O7 phosphor

The presented study deals with white light emission from Dy3+-activated Ba2ZnSi2O7 phosphors with a variable concentration of the dopant (0.1–2.5 mol.%). Ba2ZnSi2O7:Dy3+ phosphors are prepared using the modified solid-state synthesis method. The structural analysis of phosphors was conducted using the powder X-ray diffraction analysis (XRD), and refined parameters were calculated using the match software. Morphology and particle size were analysed using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Intense white light emission with the Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (0.30, 0.33) was achieved for an optimal doping concentration of 1.5 mol.%. Highest emission intensity was obtained for the 487, 544 and 594-nm emission, indicating its potential applicability in the fields of lighting and displays. Thermoluminescence (TL) glow curves are composite in nature and a broad band, found at 300°C, was deconvoluted by the computerized glow curve deconvolution program to calculate its kinetic parameters. The glow curve intensity increases upon increasing the UV exposure time. This study is useful in detecting trap parameters and TL dosimeters.

Manipulation of parity and polarization through structural distortion in light-emitting halide double perovskites

Halide perovskite materials recently attracted wide attention for light-emitting applications. The intense white light emission and excited state lifetimes greater than 1 μs are the hallmarks of a good light-emitting material. Here, we provide a clear design strategy to achieve both of these aforementioned properties in a single material via the introduction of octahedral asymmetry in halide double perovskites Cs2AgMCl6 through iso-trivalent substitution at the M site. In the substituted Cs2AgMCl6, the presence of mixed M3+ sites distorts the [AgCl6]5- octahedra, affecting the parity of the valence and conduction band edges and thereby altering the optical transitions. The distortion also creates a local polarization that leads to an effective photogenerated carrier separation. Considering perovskite series with three M3+ cations, namely Bi3+, In3+ and Sb3+, the mixed trivalent cationic compounds with specific ratios of In3+ and Bi3+ show white light emission with intensity nearly 150 times larger than that of the parent compounds, and are characterised by excited state lifetimes nearing 1 μs. Using single crystal X-ray diffraction, far-infrared absorption, steady-state and time-resolved photoluminescence, bias-dependent photoluminescence, P-E loop traces and density-functional theory calculations, we hence demonstrate the role of octahedral distortion in enhancing white light emission and excited state lifetimes of halide double perovskites.

Laser induced hydrogen emission from ethanol with dispersed graphene particles

Efficient hydrogen emission from ethanol with disperse graphene foam particles by using a continuous wave infrared laser diode is reported. The products of ethanol dissociation - hydrogen, methane and carbon oxide were measured using mass spectrometry. It was found that the most efficient generation of hydrogen was observed when graphene particles were irradiated by a focused laser beam proceeded at the surface of ethanol solution. The process was assisted by intense white light emission resulting from the laser induced multiphoton ionization of graphene combined with the simultaneous emission of hot electrons. The hot electron emission enables the efficient dissociation of ethanol molecules located close to the solution surface with graphene foam particles.

N–SrTiO3/p-GaN heterojunctions: A white light-emitting diode with a broad luminescence spectrum

We report a white light-emitting diode (LED) based on the n-SrTiO3 (n-STO)/p-GaN heterojunction. The n-STO/p-GaN heterojunction LED shows the good rectification characteristics in the current−voltage measurements and an intense white light emission with a broad luminescence spectrum in electroluminescence (EL) measurements. There are two strong and broad emission bands at the regions from blue to red (450–650 nm, center located at ~525 nm) and from ultraviolet to blue (350–450 nm, center located at ~410 nm), which are respectively derived from the p-type GaN and n-type STO layers. The photoluminescence (PL) spectra indicate that the n-STO film has an emission band from ultraviolet (UV) to blue which is associated with the near band-edge emission and defect-related radiative recombination, and the p-GaN layer has an emission band from blue to red. Our results suggest that n-STO/p-GaN heterojunction is an alternate and effective heterostructure to achieve LEDs with high intense white light emission.

Synthesis, structure, and photoluminesence of the chloridoaluminates [BMIm][Sn(AlCl4)3], [BMPyr][Sn(AlCl4)3], and [BMIm][Pb(AlCl4)3

[BMIm][Sn(AlCl4)3] (1) ([BMIm]: 1-butyl-3-methylimidazolium), [BMPyr][Sn(AlCl4)3] (2) ([BMPyr]: 1-butyl-1-methyl-pyrrolidinium), and [BMIm][Pb(AlCl4)3] (3) are obtained by reaction of SnCl2/PbCl2 in [BMIm]Cl/[BMPyr]Cl/AlCl3-based ionic liquids. The colourless crystals of the title compounds contain infinite 1∞[M(AlCl4)3]n- chains (M: Sn, Pb) that are separated by the voluminous [BMIm]+/[BMPyr]+ cations. The central Sn2+/Pb2+ is coordinated by chlorine in the form of distorted squared anti-prismatic polyhedra. Each Cl atom, in turn, is part of an [AlCl4]- tetrahedron that interlinks Sn2+/Pb2+ to the chain-like building unit. In addition to the novel structural arrangement, all title compounds surprisingly show intense white-light emission. Although Sn2+ and Pb2+ are well-known as dopants in conventional phosphors, efficient luminescence via s-p-transitions of compounds containing Sn2+/Pb2+ in molar quantities and as regular lattice constituents is rare. The emission of [BMIm][Sn(AlCl4)3] and [BMPyr][Sn(AlCl4)3] is very efficient with quantum yields of 51 and 76%, which belong to the highest values known for s-p-based luminescence of Sn2+.

Crystal structure and photoluminescence investigations of Y3Al5O12:Dy3+ nanocrystalline phosphors for WLEDs

Dy3+-doped Y3Al5O12 (YAG) nanophosphors have been effectively synthesized via facile solution technique at 600 °C using urea as a fuel and calcined at 950 and 1050 °C for further analysis. Powder X-ray diffraction (PXRD), Fourier transformation infrared (FTIR), transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and photoluminescence (PL) studies were employed to confirm the synthesis, structural and luminescence properties of the phosphors. PXRD patterns of Y3Al5O12 and Y3Al5O12:Dy3+ corresponds to JCPDS card No. 73–1370 having cubic unit cell and Ia3̅d space group, which were also confirmed by Rietveld refinement analysis. TEM images display the homogeneously disseminated nanocrystals with smooth morphology and particle size in 50–85 nm range. Energy dispersive X-Ray analysis (EDAX) proposed the pure synthesis of materials with presence of only elements integrated within host lattice. The photoluminescence emission (PL) spectra of YAG:Dy3+ nanophosphors exhibit strong emission owing to 4F9/2→6F15/2 (480 nm) and 4F9/2→6F13/2 (577 nm) under 352 nm excitation. Critical distance confirmed that the energy transfer occurs via multipolar interaction mechanism. CIE chromaticity diagram displays the intense white light emission for the phosphors. These investigations suggest the potential applications of YAG:Dy3+ nanocrystals in white light emitting diodes (WLEDs).

Flexibly transparent luminescent organic-inorganic-polymer composite films: Intense full-color emissions at a single excitation wavelength

A versatile method utilizing organic-inorganic-polymer composite materials has been developed for the fabrication of both white-converting films and flexibly transparent full-color luminescent films. In this study, a single organic UV-harvester, salicylate (sal), was intercalated into the gallery of Eu3+-doped layered terbium hydroxide (LTbH:Eu), Tb3+-doped layered yttrium hydroxide (LYH:Tb), and layered yttrium hydroxide (LYH), to create three primary color emitting hybrids, sal-LTbH:Eu, sal-LYH:Tb, and sal-LYH. By adopting an identical organic sensitizer, its S0 → S1 (π, π*) transition was able to produce characteristically intense 5D0 → 7FJ Eu3+ red-emissions, as well as 5D4 → 7FJ green-emissions of Tb3+, through energy transfer to host matrices without a change in excitation wavelength. Despite a considerable energy difference between the 5D0 resonance energy level of Eu3+ and the lowest triplet state of salicylate, the energy transfer of Tb3+ to Eu3+ in the LTbH:Eu matrix resulted in the intense red-emission observed for Eu3+. In contrast, when the salicylate was included into the interlayer gallery of LYH (containing no activator ions), its typical blue-emission was found preserved at the same excitation wavelength. Moreover, these salicylate-intercalated hybrids, prepared by a facile aqueous solution route at room temperature, were well dispersed in water to form luminescent colloidal solutions. By mixing individual hybrid colloids at certain specific ratios, an intense white-light and full-color emission was successfully achieved at a low excitation energy (λ = 365 nm) using a commercial UV-lamp. Polyvinyl alcohol (PVA) was also employed to produce flexibly transparent luminescent composite films via simple casting of desired hybrid-dispersed solutions. Full-color generation and white-light converting behavior was demonstrated using the as-synthesized organic-inorganic-polymer composite films.

Multiple Energy Transfer in Luminescence-Tunable Single-Phased Phosphor NaGdTiO4: Tm3+, Dy3+, Sm3.

Advances in solid-state white-light-emitting diodes (WLEDs) necessitate the urgent development of highly efficient single-phase phosphors with tunable photoluminescence properties. Herein, the Tm3+, Dy3+, and Sm3+ ions are incorporated into the orthorhombic NaGdTiO4 (NGT) phosphors, resulting in phosphors that fulfill the aforementioned requirement. The emission spectrum of Tm3+ ions overlaps well with the adsorption spectra of both Dy3+ and Sm3+ ions. Under the excitation at 358 nm, the single-phase NaGdTiO4: Tm3+, Dy3+, Sm3+ phosphor exhibits tunable emission peaks in the blue, yellow, and red regions simultaneously, resulting in an intense white-light emission. The coexisting energy transfer behaviors from Tm3+ to Dy3+ and Sm3+ ions and the energy transfer from Dy3+ to Sm3+ ions are demonstrated to be responsible for this phenomenon. The phosphors with multiple energy transfers enable the development of single-phase white-light-emitting phosphors for phosphor-converted WLEDs.

Current Driven Light Emission of Sodium Silica Gels

The intense white light emission of sodium silica gels under AC excitation was investigated. Its spectrum consisted of two sharp narrow sodium yellow lines centered at 588 nm and 590 nm and broadband emission with a maximum at around 600 nm. Temperature of the light-emitting sample has been measured to be relatively low about 150 °C. It was observed that white light electroluminescence intensity increased exponentially with the applied current. The origin of current stimulated white lighting of sodium silica gel is discussed in terms of avalanche ionization.

Fluorinated Spacers Regulate the Emission and Bandgap of Two-Dimensional Single-Layered Lead Bromide Perovskites by Hydrogen Bonding.

In this work, four kinds of two-dimensional single-layered F-substituted ethylammonium lead halide perovskites (LHPs, (FxCH3-xCH2NH3)2PbBr4, x = 0, 1, 2, and 3) are successfully synthesized. The introduction of terminal F atoms promotes the formation of an inter- and intramolecular hydrogen bonding network, which has a great impact on the configuration of F-substituted EA, the interlayer spacing, and distortion of inorganic layers. Among these four as-prepared samples, (FCH2CH2NH3)2PbBr4 shows the smallest bandgap (∼2.72 eV) and best photoconductivity because of the interlayer electronic coupling. Owing to the strong coupling between excitons and lattice, intense white light emission (quantum yield: 12%) is observed for (F2CHCH2NH3)2PbBr4. Benefiting from the hydrophobic nature of F-C bonds, (CF3CH2NH3)2PbBr4 presents a greatly improved stability toward moisture. These findings reveal that constructing inter- and intramolecular interaction can serve as an effective approach for tuning the broadband emission and the interlayer conductivity of single-layered LHPs.

Bright white-light emission and multicolor outputs in time domain from a core-shell structured microcrystal

Intense white-light color emission of lanthanide-doped core-shell structured particles at microscale level was presented under 980 nm excitation. The prepared NaYF4:Yb/Er@ NaYF4:Yb/Tm microcrystals not only can effectively prevent the deleterious cross-relaxation that occurs between the Er3+ and Tm3+ due to the location of the activator ions within different layers, but also possess a high luminescence efficiency due to dimensions of the micro-scale structure. The core-shell structured microcrystals presented satisfactory capacity for color control in the white region. The results show great potential in attaining white light-emitting diodes within the field emission display on specific device applications. Furthermore, the core-shell microcrystals emit white-light that presents obvious and distinct lifetimes of green, red, and blue emissions, which could achieve multicolor emissions by setting a suitable delay time. This feature demonstrates that the core-shell structured microrods offer practical use as security ink to prevent forgery, such as in identifying currency.

Anthracene-Resorcinol Derived Covalent Organic Framework as Flexible White Light Emitter.

The ordered modular structure of a covalent organic framework (COF) facilitates the selective incorporation of electronically active segments that can be tuned to function cooperatively. This designability inspires developing COF-based single-source white light emitters, required in next-generation solid-state lighting. Here, we present a new anthracene-resorcinol-based COF exhibiting white light emission. The keto-enol tautomers present in the COF give rise to dual emission, which can be tuned by the O-donor and N-donor solvents. Importantly, when suspended in a solid polymer matrix, this dual emission is retained as both tautomers coexist. A mere 0.32 wt % loading of the COF in poly(methyl methacrylate) (PMMA) gives a solvent-free film with intense white light emission (CIE coordinates (0.35, 0.36)). From steady-state and time-resolved studies, the mechanism of the white light emission has been unambiguously assigned to fluorescence, with the blue emission originating from the π-stacked columns of anthracene, and the mixture of red and green from the keto-enol tautomerized resorcinol units. The study introduces the COF as a new class of readily processable, single-source white light emitter.

Intense Upconverted White Light Emission from Tm3+ - Er3+ - Yb3+ Doped Zinc Tungsten Tellurite Glasses

The different amount of rare earth ions doped zinc tungsten tellurite glasses with the compositions (70-x-y-z)TeO 2 – 20ZnO – 10WO 3 – xEr 2 O 3 – yTm 2 O 3 – zYb 2 O 3 (x = 0.3, 0.5; y = 0.3, 0.5; z = 3) have been synthesized using melt quenching technique. Blue, green, red and infrared luminescence via energy transfer and frequency upconversion mechanisms in Tm 3+ /Er 3+ /Yb 3+ triply-doped zinc tungsten tellurite glasses were investigated under single 975 nm diode laser excitation. Intense blue (Tm 3+ : 1 D 2 → 3 F 4 , 1 G 4 → 3 H 6 ; 477 nm), green ( 2 H 11/2 , 4 S 3/2 → 4 I 15/2 ; 525 nm and 549 nm), red (Er 3+ : 4 F 9/2 → 4 I 15/2 , Tm 3+ : 1 G 4 → 3 F 4 ; 659 nm) and infrared (Tm 3+ : 1 G 4 → 3 H 5 , 3 H 4 → 3 H 6 ; 807 nm) emissions were observed simultaneously at room temperature. Intense white light emission from all samples was observed with CCT values higher than 6500 K and CRI values lower than 80. The CIE coordinates of the emitted white light were found to shift to yellowish-greenish region with increasing pumping power. The possible energy transfer and upconversion mechanisms are discussed and plausible explanations are made.

White light emission from Er2O3 nano-powder excited by infrared radiation

Phosphors of Er2O3 nano-crystalline powders were synthesized by the thermal decomposition method. The structural properties of the nano-powders were investigated with XRD and HRTEM measurements. The cubic phase with a = 10.540 Å was the only phase observed. The average crystalline sizes and the widths of the grain size distribution curves were determined to be 27.2, 18.7 and 9.7 nm, respectively. The spectroscopic properties of the Er2O3 nano-powder were studied by measuring the luminescence, decay and rise patterns under 808 and 975 nm diode laser excitations. A peculiar effect of the pressure was observed since an optically active ion (Er) is part of the complex and not a dopant. A broad band of the white light emission combined with blue, green and red up-conversion emission bands of Er3+ ions were observed at 0.03 mbar pressure under both excitation wavelengths. Only, an intense broad band white light emission was observed from these nanocrystals at atmospheric pressure. Rising patterns show that the white light intensity reaches its maximum value more rapidly under 975 nm excitation although it decays slower than that of 808 nm excitation. The color quality parameters such as the color coordinate (CRI), correlated color temperature and the color rendering index were found to vary with both the excitation wavelength and the ambient pressure indicating that these nanocrystals could be considered good white light emitting source under the infrared excitations.