Intense White Emission Research Articles

Pressure-triggered intense natural white emission via controllable distortions of antimony chloride dimers

Zero-dimensional (0D) hybrid metal halides (HMHs), featured with unique self-trapped exciton (STE) emissions, are emerging photoluminescence (PL) materials for photoelectronic applications. Compared with metal-halogen monomers, dimeric units in 0D HMHs possess more structural flexibility and less spatial confinement of excitons, creating new opportunities for PL engineering. Herein, high pressure is employed on 0D (C3H12N2)2Sb2Cl10 to controllably distort inter- and intra-octahedral structures within [Sb2Cl10]4− dimers. Intense natural white emission is achieved with dramatically increased photoluminescence quantum yield from less than ≈1% to 74.2 %. The high-pressure emission of (C3H12N2)2Sb2Cl10 is proven to originate from the STE recombination from triplet states with varied emission equilibrium, as well as the promoted excitonic trapping with restrained nonradiative recombination. This work offers valuable insights into the structure effects on STE emission and the transition mechanisms of metal-halogen dimers, which are crucial for developing novel metal halides for illumination.

High-contrast multicolour photoswitching based on dithienylethene Schiff base with a hydrazinylquinoline moiety

A new asymmetrical photochromic diarylethene DTE-HQo composed of a 2-hydrazinoquinoline moiety as the binding unit for ions and dithenylethene as a photoswitching trigger was reported. DTE-HQo displayed favourable photochromism upon irradiation with UV/vis light. Its fluorescent behaviour could be efficiently modulated by light, Zn2+, Cd2+ and HSO4−. The binding of Zn2+ induced a strong fluorescence peak at 510 nm in DTE-HQo due to the formation of a 1:2 complex [Zn2+ + 2DTE-HQo], resulting in a notable colour change from dark to intense white emission. Triggered by Cd2+, DTE-HQo formed a 1:1 complex [Cd2+ + DTE-HQo], leading to an enhanced emission intensity by 21-fold with an emission peak red-shifted from 461 nm to 514 nm. Unexpectedly, [Zn2+ + 2DTE-HQo] underwent hydrolysis when stimulated with water, generating a yellow-emitting complex [Zn2+ + DTE-HQo]. This color change easily distinguishes it from Cd2+ complex. Additionally, DTE-HQo showed high selectivity towards HSO4− and exhibited distinct “turn-on” fluorescence with a colour change from dark to bright blue upon stimulation. Moreover, the strong emission complexes of DTE-HQo with Zn2+, Cd2+ and HSO4− could be effectively quenched during the photocyclization process. Therefore, DTE-HQo can serve as an unimolecular multicolour photoswitching chemosensor, offering potential applications as a multifunctional probe for detecting Zn2+, Cd2+ and HSO4−.

Highly bright full-color emission from dye-doped silica nanoparticles with prevention of dye self-quenching

Although fluorescent dye-doped silica nanoparticles (SiOx NPs) have been widely studied for a broad range of optical probes and devices, it is still challenging to fabricate highly bright dye-doped SiOx NPs because the luminescence quantum yields of dye-doped SiOx NPs are often lower than those of the dye alone. Herein, we report highly bright full-color emissions from dye-doped SiOx NPs that prevent dye self-quenching. Green and red fluorescence-emitting dye-doped silica nanoparticles (G-SiOx and R-SiOx NPs) were synthesized from 3-(aminopropyl) triethoxysilane (APTES) and fluorescence dyes (fluorescein, Rhodamine B). The quantum yields (QY) of G-SiOx and R-SiOx NPs were 80.9% and 25.5%, respectively; doping these dyes into the SiOx NPs did not decrease the QY values of the dyes. The combination of bule luminescent SiOx NPs (QY = 32.3%) with G-and R-SiOx NPs displayed an intense pure white (x = 0.33, y = 0.33) fluorescence emission.

Photoluminescence of SiO2:Eu and SiON:Eu films: Color selection through activating emissions from SiOx, Eu3+, and Eu2+

Photoluminescence (PL) from Eu-doped SiO2 (SiON) thin films sputter-deposited in O2, H2O vapor, or a mixture of O2 and N2 gases was characterized by excitation at a wavelength of 325 nm. The SiO2 films deposited at 500 °C with O2 contained small amount of α-quartz nanocrystals. The primary condition for either or both of the Eu3+ and Eu2+ emissions to appear was Eu content between 1 and 3 at.%, and 2.5 at.% gave the maximum emission intensity of Eu3+. The PL spectra showed only the Eu3+ emission when the films were deposited at room temperature (RT) and subsequently post annealed in an O2 atmosphere. Changing the annealing atmosphere from O2 to a vacuum and annealing at temperatures above 600 °C resulted in an intense broad violet emission signal peaking at 390 nm along with the Eu3+ emission signal. This violet emission originated from reduced SiOx species. When deposited at RT, similar temperature-dependent emission properties were obtained regardless of the reactive gas (H2O vapor or a mixture of O2 and N2). Complete transformation of Eu3+ into Eu2+ occurred when deposition was carried out at temperatures between 400 and 500 °C; a blue emission at around 467 nm was predominant from the SiO2:Eu2+ films. Deposition in the O2 and N2 gas mixture at elevated temperatures produced SiON:Eu2+ films, from which an intense white emission band peaking at 525 nm and ranging between 400 and 650 nm was observed.

Crystal phase modified blue upconversion on Tm3+/Yb3+:BCZT ceramic phosphor benefits multifunctionality in white-light applications.

Rare earth (RE) doped perovskite oxide hosts especially titanates, are promising phosphor materials in terms of white-light emission owing to their extraordinary properties such as an exceptional hosting environment for RE-ions and a switchable crystal phase near the phase boundary. Here, we report a new strategy of crystal phase modification to enhance the blue upconversion (UC) efficiency to such an extent that the combinational mixing of blue and green/red-emitting phosphor gives intense white emission. The Lead free (Ba0.85Ca0.15)(Zr,Ti)O3 ceramics were synthesised at different sintering temperatures by incorporation of Tm3+/Yb3+ ions as dopants. The UC quantum efficiency of the Tm3+/Yb3+:BCZT sample sintered at 1300 °C was recorded at different excitation power densities. It was observed that the crystal phase transformation from tetragonal to rhombohedral symmetry in the sample near the phase boundary plays a cruicial role in improving the quantum efficiency. White-light emission applications were demonstrated by preparing biphasic samples with powder mixing of a BCZT:Tm3+/Yb3+ (blue-emitting) + BCZT:Er3+/Yb3+ (green/red-emitting) phosphor, and their composition were optimised at a mixed ratio. Thereafter, photometric characterization (CIE chromaticity, colour purity and corelated colour temperatures) was performed, and it indicated the suitability of the current biphasic samples in direct white-light (cooler) applications on an industrial scale. Crystal phase modified blue emission efficiency enhancement is a key feature of this work, which helps to generate approximately pure white-light with ideal chromacity (∼0.333, 0.343) emission when Tm3+/Yb3+:BCZT is mixed with a green emitting BCZT:Er3+/Yb3+ phosphor.

Photoluminescent Properties of Hydroxyapatite and Hydroxyapatite/Multi-Walled Carbon Nanotube Composites

Hydroxyapatite (HAp) and hydroxyapatite/multi-walled carbon nanotube (MWCNT) composites were obtained by the co-precipitation method, followed by ultrasound-assisted and microwave radiation and thermal treatment at 250 °C. X-ray diffraction (XRD) confirmed the presence of a hexagonal phase in all the samples, while Fourier-transform infrared (FTIR) spectroscopy elucidated the interaction between HAp and MWCNTs. The photoluminescent technique revealed that HAp and the composite with non-functionalized MWCNTs present a blue luminescence, while the composite with functionalized MWCNTs, under UV-vis radiation shows an intense white emission. These findings allowed presentation of a proposal for the use of HAp and HAp with functionalized MWCNTs as potential materials for optoelectronic and medical applications.

White light emission from Sm-doped YAG ceramic controlled by the excitation wavelengths

This work reports, for first time, on optically-driven white light emission from samarium-doped yttrium aluminum garnet ceramic, Sm-doped YAG. Nanocrystalline Sm-doped YAG sample has been prepared via co-precipitation method then transformed to bulk ceramic by sintering process using Spark Plasma Sintering (SPS) technique. X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) are used to characterize the crystal structure of the nanocrystals. The micro-grains of the obtained ceramic have been demonstrated by scanning electron microscope (SEM). Photoluminescence (PL) and cathodoluminescence (CL) spectroscopies have been performed on the ceramic sample. It is found that the PL spectral features are strongly dependent on the excitation wavelength. Remarkable PL spectral overlapping between bluish-green band and reddish-orange lines related to host defects/impurities and Sm ions, respectively, has been obtained. In addition, controlling the relative PL spectral contributions from the host-related emission and Sm ions has been achieved by changing the excitation wavelengths. This led to manipulate the emission color coordinates as investigated by chromaticity diagram. Moreover, under certain excitation wavelengths, an intense white emission is observed with a naked eye. The origin of the white emission has been discussed in light of specific PL spectral overlapping from the host and Sm ion contributions. This work emphasizes on the role played by the host defects/impurities in the optical properties of ceramic materials that can be exploited in several lighting applications.

Infrared laser stimulated broadband white emission of transparent Cr:YAG ceramics obtained by solid state reaction sintering

In the present work, the Light Induced White Emission (LIWE) was investigated as one of the sources of laser loss in transparent Cr:YAG ceramics. We have found that transparent Cr:YAG ceramics is capable of generating bright LIWE at excitation powers above a certain threshold. Intensity of LIWE strongly depends on the excitation power and ambient pressure. The host temperature estimated from Cr3+ luminescence was found to be below 600 °C, while the most intense white emission was found between 50 and 400 °C. The mechanism of the laser induced white emission was discussed in terms of Intervalence Charge Transfer (IVCT) in chromium mixed valence pair.

Shape controllable ultrasound assisted fabrication of CaZrO3:Dy3+ hierarchical structures for display, dosimetry and advanced forensic applications

Herein, we report hierarchical arrow-like structures of CaZrO3:Dy3+ (1−11 mol %) are prepared by sonochemical route using bio template as a surfactant. High purity and crystallinity of the product was obtained in sonochemical route when compared to conventional methods. Morphological results showed arrow-like structures which are highly reliant on many experimental parameters such as, sonication time, bio-template concentration, sonication power, pH and surfactant to water ratio. The photoluminescence emission spectra consist of sharp peaks at ∼481 nm (blue), 575 nm (yellow) and 665 nm (red), which ascribed to 4F9/2→6H15/2, 4F9/2→6H13/2 and 4F9/2→6H11/2 transitions of Dy3+ ions, respectively. The decrement in the photoluminescence emission intensity after 7 mol % of Dy3+ ion concentration was clearly noticed, which may due to concentration quenching. The photometric properties of the prepared samples showed intense white emission with high color purity. Thermoluminescence glow curves of CaZrO3:Dy3+ (7 mol %) showed broad and intense peak at ∼143 °C at a warming rate of 2 °C s−1. Thermoluminescence profile reveals the linear dependence with dose, least fading and highly reproducible. The optimized powders are employed to image the latent fingerprints with higher resolution on various porous, non-porous and semi-porous surfaces. The aforementioned results clearly indicate that the optimized hierarchical structures are effectively used in radiation dosimetry, display devices and advanced forensic applications.

White electroluminescence from SiNx thin films by a PECVD equipment using dichlorosilane precursor and study of emission mechanism

ABSTRACT In the present work SiNx thin films, grown by PECVD technique using dichlorosilane, were used in electroluminescent device (EL) structure. Series of experiments were carried out by varying the flow of H2 and SiH2Cl2, and after all the depositions and subsequent result analysis, a set of conditions were identified as M1, M2, M3, and M4 according to the physical thickness of the samples, their PL emission color and intensity of the emission. M3 and M4 conditions were identified as of key interest because of their intense whiteemission. After the photoluminescence (PL) analysis, EL was carried out, and a device structure was fabricated for the study. Role of quantum confinement effect was found for the white emission from the calculated nanocrystals from 2.5 to 5 nm. These results could be an important step for the establishment of optoelectronic devices such as silicon LEDs in the near future.

Screening Approach for the Discovery of New Hybrid Perovskites with Efficient Photoemission

AbstractOwing to quantum confinement, low‐dimensional hybrid perovskite materials have recently shown a great potential for applications in optoelectronics. Such compounds can exhibit broad‐ or narrow‐band light emission, low‐temperature solution processability, high thermal stability, and relatively high photoluminescence quantum yields (PLQY). However, the search for efficient phosphors with a specific set of characteristics remains difficult because the family of hybrid perovskites consists in an extremely large chemical system (i.e., different halides, metals, and organic molecules), and optical properties are not predictable prior to material synthesis and characterization. Here, is proposed a simple approach to screen a significant amount of new hybrid lead halide perovskites. The synthetic method by fast crystallization at low temperature enables the rapid identification of the materials exhibiting the targeted photoluminescence properties. This approach is tested for the discovery of hybrid lead halide perovskites with efficient white‐light emission. Among 100 newly synthesized compounds, 5 exhibit intense white emission, and the in‐depth characterization of a selected candidate shows high color rendering index (CRI) = 78 and a PLQY of 9%, which is equivalent to the record reported for hybrid perovskites. This compound exhibits a new structure type for warm white‐light emitting hybrid perovskites with chains of corner‐sharing PbX6.

Photo‐Thermo‐Refractive Glasses Doped with Silver Molecular Clusters as Luminescence Downshifting Material for Photovoltaic Applications

AbstractSilver nanostructures, including molecular clusters and plasmonic nanoparticles, attract much attention due to their unique optical properties and potential applications in various fields. Glasses doped with silver molecular clusters are known to possess bright luminescence under UV excitation, which opens up prospects of using the glasses as solar spectral converters to overcome poor spectral response for most of photovoltaic cells in the short‐wavelength region. In this study, silver molecular clusters are formed in photo‐thermo‐refractive glass matrix both by UV irradiation and by Na+↔Ag+ion exchange and optically characterized. Photo‐thermo‐refractive glasses doped with silver molecular clusters, independently on silver introduction method, are shown to demonstrate broad absorption in the UV, intense white emission under excitation at 360 nm, and high photoluminescence quantum yield that meet requirements for luminescence downshifting materials. Despite this, only photo‐thermo‐refractive glass with silver molecular clusters uniformly distributed in the glass volume enhances the output power of a silicon photovoltaic cell, thus showing the potential for future application of photo‐thermo‐refractive glasses in photovoltaics, particularly in case of further experiments.

Multifunctional Dy (III) doped di-calcium silicate array for boosting display and forensic applications

Latent fingerprints (LFPs) are the major physical evidences for the identification of individuals during crime spot investigation. Till date, numerous methods were followed to visualize LFPs. However, simple, accurate, and cost-effective method has wide scope in advanced forensic field. In our work, Ca2SiO4:Dy3+ nanopowders (NPs) were fabricated via solution combustion route. The optimized sample was employed for the visualization of overlapped LFPs by the cost effective powder dusting method. The obtained results reveals the complete three levels of ridge characteristics with high sensitivity, reproducibility, selectivity, and reliability on various complex surfaces. The photoluminescence (PL) spectra consist of intense peaks at ∼ 480 and 574 nm owing to 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 4f transitions of Dy3+ ions, respectively. The photometric properties confirm that the samples exhibit intense white emission with high color purity. Therefore, the prepared NPs could be a definitive choice as an advanced luminescent NPs for forensic, solid state lighting and portable FED devices.

A Novel Warm White Light Phosphor Ca2Al2SiO7:Dy3+ for White Light-Emitting Diodes

The white light emitting phosphor Ca2Al2SiO7:Dy3+ was synthesized by a conventional high-temperature solid-state method. X-ray diffraction and photoluminescence spectra were used to characterize the as-synthesized phosphor. Strong excitation peaks of Ca2Al2SiO7: Dy3+ were found around 350-370 nm, which matched well with the UV LED chip. Under 350 nm excitation, Ca2Al2SiO7: Dy3+ phosphor can exhibit an intense warm white emission by combining the two emission peaks locating at blue region (485 nm) and yellow region (575 nm), attributed to the characteristic F-4(9/2)-H-6(15/2) and F-4(9/2)-H-6(13/2) transition of Dy3+. The critical doping content of Dy3+ is 7%, and the intensity of the emission increased proportionally as the Dy3+ concentration increased until it was reached at 7%. When the doping concentration occurred from 7% to 9%, the luminescence intensity gradually reduced. Moreover, The CIE coordinates and the correlated color temperature (CCT) are also investigated in this work. The result shows that the optimum phosphor Ca1.93Al2SiO7:0.07Dy(3+) exhibits excellent color purity with chromaticity coordinates of (0.375, 0.391) and the CCT of 4231 K and could be considered as potential research value on white-LEDs.

Sol-gel-nitridation preparation and photoluminescence properties of Dy3+-doped M2Si5N8 (M=Ca, Sr, Ba) phosphors for white light emitting diodes

M2Si5N8:Dy3+(M=Ca, Sr, Ba) nitride phosphors with different Dy3+ ion concentrations were prepared via a novel sol-gel-nitridation method involving an annealing step at 1300 or 1400°C. The X-ray diffraction patterns indicate that the structure of these phosphors is in good agreement with the standard M2Si5N8 crystal structure. The photoluminescence spectra recorded for the prepared phosphors exhibited an intense white emission consisting of a blue emission peak (485nm) and a yellow emission peak (582nm), which are attributed to the characteristic 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of the Dy3+ ions, respectively. When using a different alkaline earth metal, the structure of the resulting M2Si5N8 phosphors changed and the luminescence was also affected. The chromaticity coordinates of the prepared Sr2Si5N8:Dy3+, Ca2Si5N8:Dy3+, Ba2Si5N8:Dy3+ phosphors with blue and yellow emission peaks were (x=0.391, y=0.397), (x=0.448, y=0.433) and, (x=0.42, y=0.414), respectively, which are all close to the standard white light coordinates (0.33, 0.33). The lifetime values of the obtained Ca2Si5N8:Dy3+, Sr2Si5N8:Dy3+ and Ba2Si5N8:Dy3+ phosphors were determined to be 0.028, 0.0167 and 0.0113ms, respectively.

Intense white emission from a single-upconversion nanoparticle and tunable emission colour with laser power

The development of upconversion nanoparticles with tunable emissions, particularly white colour emission, has always been at the forefront of colour display technologies.

Green synthesis of Y2O3:Dy3+ nanophosphor with enhanced photocatalytic activity

Facile and green route was employed for the synthesis of Y2O3:Dy3+ (1–11mol%) nanostructures (NSs) using Aloe vera gel as fuel. The formation of different morphologies of Y2O3:Dy3+ NSs were characterized by SEM, TEM and HRTEM. PXRD data and Rietveld analysis evident the formation of single phase Y2O3 with cubic crystal structure. The influence of Dy3+ ion concentration on the structure morphology, UV absorption, PL emission and photocatalytic activity of NSs were investigated. NSs exhibited an intense warm white emission with CIE chromaticity coordinates (0.32, 0.33) and average CCT value ∼5525K which corresponds to vertical day light. The control of Dy3+ ion on Y2O3 matrix influences the photocatalytic decolorization of Metanil Yellow as a model compound was evaluated. The enhanced photocatalytic activities of core shell structured Y2O3:Dy3+ (1mol%) was attributed to co-operation effect of dopant concentration, crystallite size, textural properties and capability for reducing electron–hole pair recombination. Further, the recycling catalytic ability of Y2O3:Dy3+ (1mol%) nanostructure was also evaluated and found promising photocatalytic performance with negligible decrease in decolorization efficiency even after sixth successive cyclic runs. Considering its green, facile synthesis and recyclable feature from an aqueous solution, the present Y2O3:Dy3+ (1mol%) nanophosphor can be considered as one of the ideal photocatalyst for various potential applications.

White light emission from NaLa(PO3)4: Dy3+ single-phase phosphors for light-emitting diodes

White light emission phosphors NaLa(PO3)4: Dy3+ were synthesized by a solid-state method. XRD analysis confirmed that all the Dy3+ doped phosphors are single phase. The photoluminescence excitation and emission spectra, concentration effect, decay property, and CIE coordinates were investigated. Strong excitation peaks of NaLa(PO3)4: Dy3+ were found around 350–400nm, which matched well with those of the near-UV LED chips. Under 350nm excitation the NaLa(PO3)4: Dy3+ exhibits intense white emission by combining the two emission peaks at 485nm and 571nm, attributed to the characteristic 4F9/2–6H15/2 and 4F9/2–6H13/2 transitions of Dy3+. The optimum doped concentration of Dy3+ ions is around 6mol% and the critical transfer distance of Dy3+ is calculated as 15.4Å. In addition, the CIE chromaticity coordinates of NaLa(PO3)4: Dy3+ phosphors are (0.2923,0.3359). The results indicate that the NaLa(PO3)4: Dy3+ phosphors have great potential as a single-component white-light-emitting phosphor for UV-light-emitting diodes.

A novel white emitting phosphor of Dy3+ doped Ca19Mg2(PO4)14 for light-emitting diodes

A series of Dy3+ doped Ca19Mg2(PO4)14 phosphors were firstly synthesized by the solid-state reaction method. The phase purity and characteristic luminescent properties are investigated in detail by X-ray diffraction refinement, photoluminescence spectra and decay times measurement. Under 365nm excitation, Ca19Mg2(PO4)14:Dy3+ phosphor can exhibit intense warm white emission with CIE chromaticity coordinates (0.400, 0.452) and low correlated color temperature (3994K). The optimal doping contents of Dy3+ in Ca19Mg2(PO4)14 is determined to be 2%. The thermal quenching property of Ca19Mg2(PO4)14:Dy3+ is also investigated and it remains 60% of the initial emission intensity even when the temperature increases to 230°C. The results show that Ca19Mg2(PO4)14:Dy3+ can be a promising single phased white emitting phosphor for UV white LEDs.

Carbon-doped SiOx nanowires with a large yield of white emission

The growth of SiOx nanowires (NWs) with intense white emission is reported. Due to carbon monoxide gas being used as a dopant precursor, carbon-doped under-stoichiometric silicon dioxide NWs are obtained. The doping of the NWs is studied by means of x-ray photoelectron spectroscopy, which allows to assess the presence of carbon atoms in the silicon oxide amorphous structure. The light emission properties are studied by means of cathodoluminescence spectroscopy, which shows three main emission bands set at 2.7 eV (blue), 2.3 eV (green) and 1.9 eV (red), resulting in the white emission.