Solid-state Lighting Applications Research Articles

Simple fabrication of novel Sm3+ doped BaGd2ZnO5 nanophosphors for flexible displays, improved data security applications, and solid-state lighting applications

In the present work, Urea-assisted combustion synthesis of BaGd2ZnO5:Sm3+ nanophosphors (BGZO:Sm NPs) with orthorhombic symmetry and cool white light luminance. According to the morphological study, the agglomerated particles had non-uniform shapes and crystallite sizes between 30 and 40 nm. The decay lifetime and quantum efficiency are found to be 0.387 ms and 51.4%, respectively. PL emission spectra can gather details about the orange-red emanation from produced NPs since they have a fine peak at 601 nm. Studies on photoluminescence (PL) also demonstrate that exchange-type interrelations are the primary mechanism for the non-radiative relaxing of energy. Finally, outstanding luminous performance is demonstrated by CIE color coordinates (0.5601, 0.3421), color purity (71%), and 1,376 K color-associated temperature (CCT). The multilevel characteristics of the phosphor-attached latent fingerprint (LFP) could be clearly identified in 404 nm light. An optimal observational environment is established by the sharp color contrast between the lines of the valley and ridge. Additionally, the impact of the NP utilized on various substrates for the visualization of LFPs is investigated. The findings demonstrate that the NP is a strong candidate for LFP visualization. Here, a flexible light-emitting material made of polydimethylsiloxane (PDMS) is used as the basis for an anti-counterfeiting (AC) method. Eventually, the ideal sample-convert PDMS flexible films with simple operation and good reusability are created, and their security level is further increased by the collaboration of colorful and distinctive characters.

Dual color luminescence of Mn2+ doped lead-free Cs3Cu2I5 perovskite phosphors and their LED solid-state lighting and anti-counterfeiting applications

Cs3Cu2I5 have recently attracted far-flung and fervency interests with the characters of low cost, high photoluminescence quantum yield, green and non-toxicity. In addition, continuous tuning of the luminescence properties could be realized in Cs3Cu2I5, which would benefit its optical applications. Herein, Mn2+ is chosen as the luminescent center into Cs3Cu2I5 through solid-state ball milling method. Its structure and photoluminescence properties have been studied by various characterization methods such as X-ray powder diffractions, fluorescence spectroscopy, and element mapping. These results showed that Mn2+ doping into Cs3Cu2I5 makes little change on the crystal structure of Cs3Cu2I5. The copper ions and manganese ions exist stably in the form of Cu+ and Mn2+, respectively. After Mn2+ doping, a new emission peak appears at 560 nm except for the intrinsic blue emission of Cs3Cu2I5, thus realizing dual color luminescence. This material also exhibits excellent thermal stability, making it suitable for solid-state lighting and anti-counterfeiting applications.

Photoluminescent studies of trivalent terbium activated magnesium metaphosphate phosphors

ABSTRACT The solution combustion route is used to synthesize a series of MgP2O6:Tb3+(0.5–3.5 mole %) phosphors. X-ray diffraction and Rietveld refinement analysis have verified the crystal purity (monoclinic symmetry) with space group P21/n and refined lattice parameters (a = 11.12 Å, b = 8.268 Å, and c = 9.902 Å), respectively. The excitation and emission features of the synthesized material (luminescent properties) are monitored using photoluminescence spectroscopy. The emission spectrum, recorded at excitation 215 nm, shows the most prominent emission peak at 545 nm, which is responsible for green colour emission. The CIE coordinates indicate that phosphors emit in the green light region. The synthesized material has conventional application in solid-state lighting under UV excitation (215 nm).

Fabry–Perot Oscillation and Resonance Energy Transfer: Mechanism for Ultralow-Threshold Optically and Electrically Driven Random Laser in Quasi-2D Ruddlesden–Popper Perovskites

The recently emerged metal-halide hybrid perovskite (MHP) possesses superb optoelectronic features, which have obtained great attention in solid-state lighting, photodetection, and photovoltaic applications. Because of its excellent external quantum efficiency, MHP has promising potential for the manifestation of ultralow threshold optically pumped laser. However, the demonstration of an electrically driven laser remains a challenge because of the vulnerable degradation of perovskite, limited exciton binding energy (Eb), intensity quenching, and efficiency drop by nonradiative recombinations. In this work, based on the paradigm of integration of Fabry-Perot (F-P) oscillation and resonance energy transfer, we observed an ultralow-threshold (∼250 μWcm-2) optically pumped random laser from moisture-insensitive mixed dimensional quasi-2D Ruddlesden-Popper phase perovskite microplates. Particularly, we demonstrated an electrically driven multimode laser with a threshold of ∼60 mAcm-2 from quasi-2D RPP by judicious combination of a perovskite/hole transport layer (HTL) and an electron transport layer (ETL) having suitable band alignment and thickness. Additionally, we showed the tunability of lasing modes and color by driving an external electric potential. Performing finite difference time domain (FDTD) simulations, we confirmed the presence of F-P feedback resonance, the light trapping effect at perovskite/ETL, and resonance energy transfer contributing to laser action. Our discovery of an electrically driven laser from MHP opens a useful avenue for developing future optoelectronics.

Enhancement of luminescence, thermal stability and quantum efficiency with Ce3+ co-doped SrMg1·06Al9·94O17:Tb3+ phosphor

In this study, the photoluminescence properties of a series of SrMg1·06Al9·94O17 (SMAO):Ce3+, Tb3+, and SMAO:Tb3+ phosphors were investigated. At an excitation wavelength of 230 nm, the SMAO:Tb3+ phosphor emitted green light at 544 nm. When Ce3+ ions were co-doped into SMAO:Tb3+, the excitation band red-shifted from 230 to 269 nm, and the emission intensity was enhanced up to approximately 28 times compared with that of Ce3+-free SMAO:Tb3+ because of the efficient energy transfer from Ce3+ → Tb3+ in the SMAO host. Moreover, with the introduction of Ce3+, the thermal stability of the phosphors improved significantly. The luminescence intensity of the SMAO:3 mol%Tb3+ phosphor at 450 K was approximately 47% of that at room temperature. With the co-doping of Ce3+ ions, the emission intensity at 450 K was as high as 67%. The internal quantum efficiency (IQE) of SMAO:3 mol%Tb3+, 3 mol%Ce3+ increased to 55.14%. The SMAO:Tb3+,Ce3+ phosphors have potential applications in solid-state lighting.

Novel red phosphor of Gd3+, Sm3+ co-activated AgxGd((2-x)/3)-0.3-ySmyEu3+0.30•(1-2x-2y)/3WO4 scheelites for LED solid-state lighting applications

Novel red phosphor of Gd3+, Sm3+ co-activated AgxGd((2-x)/3)-0.3-ySmyEu3+0.30•(1-2x-2y)/3WO4 scheelites for LED solid-state lighting applications

Effect of photoluminescence property in Li+, Ca2+, Bi3+ ions co-doped SrMoO4:Eu3+ phosphors and their Judd–Ofelt analysis for solid-state lighting applications

Effect of photoluminescence property in Li+, Ca2+, Bi3+ ions co-doped SrMoO4:Eu3+ phosphors and their Judd–Ofelt analysis for solid-state lighting applications

Pressure Regulating Self-Trapped States toward Remarkable Emission Enhancement of Zero-Dimensional Lead-Free Halides Nanocrystals.

Copper(I)-based halides have recently attracted increasing attention as a substitute for lead halides, owing to their nontoxicity, abundance, unique structure, and optoelectric properties. However, exploring an effective strategy to further improve their optical activities and revealing structure-optical property relationships still remain a great concern. Here, by using high pressure technique, a remarkable enhancement of self-trapped exciton (STE) emission associated with the energy exchange between multiple self-trapped states in zero-dimensional lead-free halide Cs3 Cu2 I5 NCs is successfully achieved. Furthermore, high-pressure processing endows the piezochromism of Cs3 Cu2 I5 NCs by experiencing a white light and a strong purple light emission, which is able to be stabilized at near-ambient pressure. The distortion of [Cu2 I5 ] clusters composing of tetrahedral [CuI4 ] and trigonal planar [CuI3 ] and the decreased Cu-Cu distance between the adjacent Cu-I tetrahedron and triangle are responsible for the significant STEs emission enhancement under high pressure. The experiments combined with first-principles calculations not only shed light on the structure-optical property relationships of [Cu2 I5 ] clusters halide, but also provide guidance for improving emission intensity that is highly desirable in solid-state lighting applications.

Thermally stable Sm3+ -doped alkali zinc alumino borosilicate (AZABS) glass for warm white light generation and w-LED applications.

Samarium ion (Sm3+ )-doped alkali zinc alumino borosilicate (AZABS) glass was synthesized via quick melt quench technique. Various spectroscopic studies like optical absorption, photoluminescence (PL) emission, PL excitation, temperature-dependent PL and PL decay kinetics were performed on the as prepared glass system. Under 402 nm excitation, three sharp bands at wavelengths 563, 599 and 645 nm corresponding to transitions 4 G5/2 → 6 H5/2 , 6 H7/2 and 6 H9/2 , respectively, can be seen in the PL emission spectra. The 0.25 mol% Sm3+ glass has the highest intensity for these emissions. The lanthanide interaction in the glass matrix is dipole-dipole in nature as was proven from Dexter's analysis. The direct bandgap of 0.25 mol% Sm3+ -doped AZABS glass was calculated to be 2.88 eV. The lifetimes of the as prepared glass range from 1.93 ms for the lowest concentration of Sm3+ to 0.75 ms for the highest. From temperature dependent PL studies, the activation energy for 0.25 mol% Sm3+ -doped AZABS glass was found to be 0.19 eV which shows high thermal stability of this glass. We propose to utilize these Sm3+ -doped AZABS glasses for white-light emitting diodes (w-LEDs) and solid-state lighting (SSL) applications.

Strong red emission in double perovskite Sr3LiSbO6: Eu3+ phosphor with high color purity for solid-state lighting applications

Intense red-emitting double perovskite Sr3LiSbO6 (SLSO) phosphor materials have been prepared by doping of Eu3+ rare earth ion using the facile solid-state reaction route. The obtained results displayed the hexagonal structure of the sample, having space group R3c. Diffuse reflectance spectra also reflected the 3.42eV optical band gap of SLSO: 2%Eu3+ which was less than that of the pure SLSO (3.5eV), consequently showing the negative Burstein Moss effect. Photoluminescence (PL) emission spectra showed a concentration quenching effect beyond the 2mol% of Eu3+ doping concentration, indicating the involvement of dipole-dipole interaction. The lifetime of the prepared phosphor was estimated by the PL decay curve; with an average decay time of 808.6 μs. Photometric studies revealed the required lesser correlated color temperature (CCT) values (<1900K) with high color purity (CP) of 99% and Commission International de’Eclairage (CIE) coordinates were located around the red region. Drawn results demonstrated that the proposed phosphor could be a promising strong red-emitting phosphor for the white light-emitting diode (wLED) based on ultra-violet UV or blue chip.

Elucidating the Mn2+ Dopant Sites in Two-Dimensional Na–In Halide Perovskite

The layered hybrid double perovskites (LDPs) possess excellent stability and environmental friendliness, which makes them remarkable semiconducting materials. Contrary to significant advancements, the nonfluorescent nature at ambient temperature and pressure is still a major hurdle in this intriguing family. Here, we demonstrate doping of the transition metal cation Mn2+ in two-dimensional (2D) (PEA)4NaInCl8 (PEA = phenylethylamine) LDP, by a solution-processed crystallization method. This results in broadband emission at ambient conditions and initial contraction followed by expansion of host lattice on increasing dopant concentration. A higher dopant feed ratio in this wide band gap material leads to the absorption at 2.95 eV due to the 6A1 (6S) → 4A1 (4G) transitions on Mn2+ centers. First-principles calculations based on density functional theory (DFT) confirm that Mn2+ in substitutional sites results in lattice contraction while interstitial site Mn2+ doping leads to lattice expansion. The potential of Mn2+ to improve optical and magnetic properties of host lattice and a deeper understanding of distribution of Mn2+dopant make these LDPs a promising material for emitters for solid-state lighting and magneto-optical applications.

All-Inorganic Zero-Dimensional Sb3+-Doped Rb2ScCl5(H2O) Perovskite Single Crystals: Efficient Self-Trapped Exciton Emission and X-ray Detection

Zero-dimensional (0D) halide perovskites have attracted extensive attention for their potential applications in solid-state lighting and X-ray detection due to their fascinating optoelectronic properties and convenient solution processability. Herein, we report the synthesis and photophysical properties of high-quality Sb3+-doped 0D Rb2ScCl5(H2O) perovskite single crystals. The pristine crystals exhibit weak yellow self-trapped exciton (STE) emission peaking at 632 nm. The emission quantum yield can be dramatically enhanced from less than 1% to about 53% via Sb3+ doping. Spectroscopic characterizations indicate that the photoluminescence enhancement is a result of the efficient energy transfer from Sb3+ to the emissive STEs. Additionally, 0.2%Sb3+:Rb2ScCl5(H2O) single crystals exhibit potential application in direct X-ray detection with a high sensitivity of 58.5 μC Gy-1 cm-2.

Interstitial Zinc Boosted Light Tunability, Afterglow, and Ultrabright White Emission in Zinc Germanate (Zn2GeO4)

To reduce the burden of solid-state lighting and phosphor-converted light-emitting diode technologies on rare earth (RE) and avoid their potential supply risks, we have developed a RE-free Zn2GeO4 (ZGeO) microcrystalline phosphor. It was synthesized by a simple and scalable solid-state reaction of ZnO and GeO2 at 1200 °C. High-temperature synthesized ZGeO demonstrated color tunable emission from bluish-white to green on changing the excitation wavelength from 265 to 335 nm with a photoluminescence quantum yield of 42 and 9%, respectively. They could also convert highly energetic X-ray to bluish-green light emission. First-principles calculations showed that bluish-white and green light emissions are linked to zinc interstitials present, respectively, in zinc (Zni2) and zinc–germanium rings (Zni1). These defects generated in large numbers via high-temperature annealing along with antisites boosted the generation of trapping centers leading to dual persistent luminescence (PerL) of white and green light for more than 60 min as well as exhibited radioluminescence. Luminescent ink based on ZGeO was fabricated and successfully tested for anticounterfeiting applications. An extra effort has been vested on making this solid-state processed ZGeO dispersible in water-soluble deep eutectic solvent which could be a game changer for its marketability. This material has great potential to become an efficient RE and dopant-free phosphor synthesized by a simple, scalable, and cost-efficient route for applications in solid-state lighting, display, and anticounterfeiting, having multifunctionalities such as PerL, tunability, and RL.

Structural and photophysical measurements of Er3+ doped Gd4Al2O9 nanophosphors for NUV excitable solid-state lighting applications

Green emitting Gd4-xAl2O9:xEr3+ [x = 1 to 6 mol%] nanophosphors were synthesized via urea assisted solution combustion (SC) synthetic pathway and characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) observations and spectrofluorophotometric measurements. The structural results obtained by XRD measurements and Rietveld refinement confirm that all prepared nanomaterials are crystallized in monoclinic structure,space group P21/c. The strongest excitation located at ∼382 nm is strongly matched to the distinct wavelength of commercially accessible NUV excitable LEDs. Under the excitation at 382 nm, all prepared samples exhibit a series of sharp emission bands centred at 411 nm (2H9/2 → 4I15/2), 528 nm (2H11/2 → 4I15/2), 558 nm (4S3/2 → 4I15/2) and 665 nm (4F9/2 → 4I15/2), corresponding to transitions of Er3+ ions. The optimum doping concentration of Er3+ ions in the host is determined to be 3 mol%. The photoluminescence lifetime (τavg)determined in Gd3.97Al2O9:0.03Er3+ phosphor is observed to be around 2.0191 ± 0.0371 ms. The calculated Commission Internationale de L’Eclairage (CIE) chromaticity coordinates for the optimized phosphor is (x = 0.305, y = 0.592), which is close to the Society of Motion Picture and Television Engineers (SMPTE) (x = 0.310, y = 0.595) coordinates. The study reveals that optimized phosphor could be a potential candidate for near ultra-violet (NUV) excited photonic appliances.

UV/blue/green converted efficient red-NIR photoluminescence in Cr incorporated MgAl2O4 nanocrystals: Site selective emission tailored through cation inversion and intrinsic defects

The UV/visible activated near-infrared (NIR) phosphors have many applications in solid state lighting, night vision devices and bio-imaging. The early research reported the red-NIR emitting phosphors doped with Cr3+ centers upon visible light excitation. Here, in this work the intense red-NIR emission and color tuning is achieved for broad excitation range (UV/blue/green) through Cr dopant induced defect centers and cation inversion in MgCr Al2O4 ( = 0.5, 1, 3, 5 and 10 mol%) nanocrystals. The Cr3+ doped MgAl2O4 nanocrystals were synthesized by combustion method through stoichiometric substitution of Mg by Cr, while most of the Cr3+ ions occupied the octahedral sites of spinel host with the formation of antisite defects, Cr3+ clusters, magnesium and oxygen vacancies. These defect centers were probed through Rietveld refinement, photoluminescence (PL), x-ray photoelectron and nuclear magnetic resonance spectra analyses. At UV excitation, the intrinsic defects played an interesting role in exhibiting the blue-violet emission attributed to host lattice defects and red-NIR emission attributed to strong/weak ligand field octahedral Cr3+ sites, via charge transfer to Cr3+ ions. The PL spectra evinced the enhanced red-NIR emission intensity upon 266 nm excitation than upon blue and green light excitation. Further, the weak ligand field site emission is found to be dominating with increase in doping concentration. Thus, Cr doped MgAl2O4 nanocrystals showed their potency of exhibiting the intense red-NIR emission and color tuning (from red purple to bluish purple and then to red color) upon UV/blue/green excitation.

Spectroscopic characterizations and investigation of Judd-Ofelt intensity parameters of Dy3+-doped Ba2La8(SiO4)6O2 near white light emitting phosphor

A series of Dy3+-activated Ba2La8(SiO4)6O2 phosphors were synthesized using the solid-state method with the objective of developing single host white light emitting phosphors for use in solid state lighting applications. The Dy3+ concentration varied between 0.01 and 0.05 mol%. The as-prepared phosphors crystal structure, optical, and photoluminescent properties (PL), along with energy transfer mechanism and luminescence decay, were investigated. The production of a single-phase Ba2La8(SiO4)6O2 with hexagonal symmetry was verified by the findings of the X-ray diffraction analysis. When the Ba2La8(SiO4)6O2: Dy3+ phosphors are exposed to ultraviolet light, they emit the characteristic yellow PL emissions caused by the 4F9/2 → 6H13/2 transition. The Judd-Ofelt (J-O) parameters (Ω2, Ω4, Ω6) were computed using the excitation spectra. The characteristics of the Dy3+ transition indicate that the asymmetric environment around the ligand was suggested by the trend, which was followed by J-O parameters. Due to the dominance of the electric-dipole transition in the luminescence spectrum, the Ba2La8(SiO4)6O2:0.03Dy3+ phosphor displayed yellowish white emission with CIE coordinates of (0.358, 0.398) and a CCT of 4724 K. The synthesized phosphor may be a useful material in the fabrication of white-emitting phosphor for LEDs application.

Practical guidance for easily interpreting the emission and physicochemical parameters of Eu3+ in solid-state hosts

Materials doped with the luminescent Eu3+ ion are attracting an ever-increasing amount of attention due to their potential applications in solid-state lighting, display devices, solar cells, or bioanalytics. But, why Eu3+? Unlike other lanthanides, its electronic features make the calculation of some physicochemical parameters quite straightforward, since they can be extracted directly from the emission spectrum. Highly appreciated for its reddish emission, the luminescent ion has also been widely used as a site-sensitive structural probe. With this in mind, this paper aims to offer easy guidance with helpful advice on how to interpret measurements of the emission spectra. It also presents the most useful tools for saving time, and gives a focused and practical explanation of the theoretical concepts involved.

Achieving bright green emission in Tb3+ doped ternary yttrate-based nanocrystalline powder for solid-state illumination applications

Tb3+ activated ternary yttrate-based nanophosphor series was fabricated via a simple solution combustion (SC) methodology. An orthorhombic crystal lattice havingspace group Pnma (62) with irregularly shaped particles with sizes between 32 and 54 nm was formed. Morphological features and elemental analysis were examined via TEM, SEM, and EDAX techniques, respectively. On near-ultraviolet (NUV) stimulation, luminescence spectra presented a bright green emission at 18315 cm−1 wavenumbers consistent with the electronic transition 5D4→7F5. The decay lifetimes, quantum efficiency, and non-radiative rates were also examined. The critical distance (Rc) originated to be 20.21 Å inducing the multipolar interrelations as the probable route for concentration quenching. The energy bandgap was examined via Diffuse Reflectance Spectroscopy (DRS). A brilliant luminescence profile is also replicated in green coordinates (0.2531, 0.4998) and 7479 K (color temperature), which has been committed to typical television, European-Broadcasting-Union (EBU), NICHIA-LED green coordinates, pc-WLEDs, and another solid-state lighting (SSL) applications.

Intense red-emitting core-active shell SiO2@CaAl2O4:Eu3+ surface sensitive fluorescent probe for dactylography applications

Rational design and synthesis of hierarchical core-shell structures have been regarded as an operative approach to enhancing the luminescence performance of the phosphors. In this work, intense red-emitting CaAl2O4:Eu3+(1–9 mol %) nanophosphors and SiO2@CaAl2O4:Eu3+(7 mol %) structures were fabricated by the ultrasound-assisted sonochemical route. The powdered x-ray diffraction studies of prepared core-shell structure confirm the monoclinic phase of the CaAl2O4 layer and amorphous SiO2 cores. The morphological and elemental analysis clearly evidences the formation of spherical and uniform core-shell structures. Upon 463 nm excitation, the photoluminescence emission spectra of CaAl2O4:Eu3+(1–9 mol %) nanophosphors consist intensive and sharp peaks at ∼ 507, 532, 551, 615, 654, 702 and 759 nm, owing to 5D1→7F2, 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3, 5D0→7F4 and 5D0→7F5 transitions of Eu3+ ions, respectively. Almost 1.6-fold enhancement in the emission intensity without any change in the spectral shape was noticed in core-shell SiO2@CaAl2O4:Eu3+(7 mol %) structures as compared to CaAl2O4:Eu3+ (7 mol %) nanophosphor, which attributed to the improved surface area, diminished surface defects and surface hanging bonds. The photometric properties signify the pure red emission of the structures and are useful for multi-functional applications. The prepared spherical and uniform-sized core-shell structures are used as fluorescent labeling material for the visualization of latent fingerprints on various surfaces. The fingerprints developed using prepared structures show excellent contrast, high sensitivity, and negligible background disruption. This work demonstrated that the synthesized core-shell structures are a versatile material and can find their practical applications in solid-state lighting and dactylography.

Tunable ultra-broadband full-visible-spectral emission of Bi3+-doped aluminate phosphors enabled by structure transformation and site occupancy engineering

Inorganic phosphors with tunable broadband emission have important applications in solid-state lighting and security anti-counterfeiting.