Dopant Emission Research Articles

Ultrabroad Near Infrared Emitting Perovskites

Phosphor converted light emitting diodes (pc‐LEDs) have revolutionized solid‐state white lighting by replacing energy‐inefficient filament‐based incandescent lamps. However, such a pc‐LED emitting ultrabroad near‐infrared (NIR) radiations still remains a challenge, primarily because of the lack of ultrabroad NIR emitting phosphors. To address this issue, we have prepared 2.5% W4+‐doped and 2.8% Mo4+‐doped Cs2Na0.95Ag0.05BiCl6 perovskites emitting ultrabroad NIR radiation with unprecedented spectral widths of 434 and 468 nm, respectively. Upon band‐edge excitation, the soft lattice of the host exhibits broad self‐trapped exciton (STE) emission covering NIR‐I (680 nm), which then nonradiatively excites the dopants. The π‐donor ligand Cl⁻ reduces the energy of dopant d‐d transitions emitting NIR‐II with a peak at ~950 nm. Vibronic coupling broadens the dopant emission. The large spin‐orbit coupling and local structural distortion might possibly enhance the dopant emission intensity, leading to an overall NIR photoluminescence quantum yield ~40%. The composite of our ultrabroad NIR phosphors with biodegradable polymer polylactic acid could be processed into free‐standing films and 3D printed structures. Large (170 × 170 mm2), robust, and thermally stable 3D printed pc‐LED panels emit ultrabroad NIR radiation, demonstrating NIR imaging applications.

Discerning the Structure-Photophysical Property Correlation in Zero-Dimensional Antimony(III)-Doped Indium(III) Halide Hybrids.

Zero-dimensional (0D) metal halide hybrids incorporating optically emissive Sb3+ dopants have received huge research attention as a result of dopant-based visible emission for lighting and scintillation applications. Indeed, there have been a plethora of reports on Sb3+ doping of indium halide (In-X)-based 0D hybrids that show strong dopant emission with varied emission wavelengths (λem) and photoluminescence quantum yields (PLQYs). However, discerning the structure-luminescence relation in these 0D-doped hybrids remains challenging because it necessitates exquisite synthetic control on the local metal (dopant) halide geometry/site asymmetry. Demonstrated here is synthetic control that allows tuning of the local metal halide geometry of the Sb3+ dopants in 0D In-X hybrids utilizing five different organic cations. Experimental analysis of the series of Sb3+-doped In-X hybrids reveals a strong correlation between the extent of local metal halide geometry distortion and their photophysical properties (λem and PLQY). Density functional theory calculations of the doped compounds, characterizing ground- and excited-state structural distortions and energetics, reveal the origin of the extent of luminescence behavior. The experimental-computational results reported herein unravel the operative structure-luminescence relation in 0D Sb3+-doped In-X hybrids, provide insight into the emission mechanism, and open up avenues toward rational synthesis of strongly emissive materials with desired emission color for targeted applications.

Introducing Ag Dopants into CdSe Nanoplatelets (NPLs) Leads to Effective Charge Separation for Better Photodetector Performance.

Solution-processed colloidal cadmium chalcogenide nanoplatelets (NPLs)-based photodetectors (PD) are promising materials for next-generation optoelectronic devices due to their excellent optical properties. Here, we report on ultrafast carrier relaxation dynamics of four monolayer (4 ML) Ag-doped CdSe (Ag: CdSe) NPLs using ultrafast transient absorption spectroscopy and their photodetectors applications. A broad dopant emission is observed at around 650 nm with a large FWHM of ~431 meV and band edge emission at 515 nm. The intragap dopant state acts as a hole acceptor, which leads to better charge separation. The ultrafast transient absorption spectroscopy study shows faster carrier recombination dynamics with a hole transfer time scale of ~10 ps in Ag-doped CdSe NPLs. This supports the excited hole capture phenomenon at the dopant state. Ag-doped CdSe NPLs-based PD performed better than undoped CdSe NPLs with detectivity and responsivity values of 1.3×1010 Jones and 2.4 mA/W, respectively.

Downshifting photoluminescence of Erbium doped NaSrZrO3 for solid-state lighting

The synthesis of novel nanophosphors exhibiting unique morphologies with high purity, stability, eco-friendliness, and a high color rendering index is crucial to meet the demands of contemporary solid-state lighting energy devices. In this investigation, we successfully synthesized Na0.2Sr0.9-xZrO3:xEr3+ perovskite nanophosphors. All samples manifested an orthorhombic structure. The crystallite size was observed to increase with rising concentrations of Er3+. The optical band gap exhibited a range of 5.19 eV to 5.36 eV with increments in doping concentration, signifying alterations in the lattice constants attributable to crystalline disorder. The downshifting PL spectra revealed both host emission bands and dopant (Er3+) emission lines. The violet – blue band was attributed to crystalline disorder while the red emission band was assigned to octahedra tilting disorder in the perovskite. The presence of Er3+ ion lines at 523 and 546 nm produced intense green light, as depicted in the CIE chromaticity diagram for all doped samples. The study affirms that the phosphors synthesized in this research possess potential for application in the development of visible green lamps for optical display devices and solid-state lighting.

Optical properties of semiconductor nanoparticles doped with 3d and 4f block elements

Doped inorganic nanoparticles (NPs) have enabled researchers across multiple disciplines to create new materials with unique optical, electronic, magnetic, electrical, chemical, and/or compositional properties. In the quest for generating newer functional materials with controlled optical and electronic properties, the use of d- and f-block elements as dopants in the inorganic NPs remain at the forefront of research. This article summarizes experiments that identify the important control parameters, in the form of NP core and surface properties, for promoting host-sensitized dopant emission from d- and f-doped inorganic/semiconductor NPs. We conclude that energy offsets between the dopant and NP electronic levels and an understanding of the charge trapping mechanisms can be used to predict dopant luminescence, and we claim that these features can be used to choose NP host materials by design, rather than by trial and error.

Alkyl chain functionalised Ir(iii) complexes: synthesis, properties and behaviour as emissive dopants in microemulsions.

Six iridium(iii) complexes of the general form [Ir(C^N)2(N^N)]X (where C^N = cyclometalating ligand; N^N = disubstituted 2,2'-bipyridine), and incorporating alkyl chains of differing lengths (C8, C10, C12), have been synthesised and characterised. The complexes have been characterised using a variety of methods including spectroscopies (NMR, IR, UV-Vis, luminescence) and analytical techniques (high resolution mass spectrometry, cyclic voltammetry, X-ray diffraction). Two dodecyl-functionalised complexes were studied for their behaviour in aqueous solutions. Although the complexes did not possess sufficient solubility to determine their critical micelle concentrations (CMC) in water, they were amenable for use as emissive dopants in a N-methyl C12 substituted imidazolium salt microemulsion carrier system with a CMC = 36.5 mM. The investigation showed that the metal doped microemulsions had increased CMCs of 40.4 and 51.3 mM and luminescent properties characterised by the dopant.

Halide exchange mediated cation exchange facilitates room temperature co-doping of d-and f-block elements in cesium lead halide perovskite nanoparticles.

This study presents a halide exchange mediated cation exchange reaction to co-dope d- and f-block elements in CsPbX3 NPs at room temperature. Addition of MnCl2 and YbCl3 to CsPbBr3 NPs induces ion exchange reactions generating the corresponding CsPbBr3/MnCl2YbCl3 NPs. In addition to the perovskite emission, the NPs display sensitized Mn2+ and Yb3+ emissions in concert spanning the UV, visible, and NIR spectral region. Structural and spectroscopic characterizations indicate a substitutional displacement of Pb2+ by the Mn2+ and Yb3+. The identity of the host halide in modulating the ion exchange reactions was also tested. An effective perovskite host NP is presented that can be used to incorporate d-f or f-f dopant combinations to realize a gamut of dopant emission lines. A charge trapping based photophysical model is developed that focuses on rational energy alignments to predict dopant emissions semi-empirically and aids the design of optimal perovskite host-multi-dopant combinations.

Platinum(II) bis(arylacetylide) complexes bearing diarylamino-substituted bipyridine ligands for solution-processable phosphorescent OLED applications.

A comprehensive investigation has been carried out on a series of complexes of the type (N^N)Pt(-CC-Ar)2, where N^N represents diarylamino-substituted 2,2'-bipyridine (bpy) ligands and -CC-Ar refers to the substituted arylacetylide ligands. The introduction of trifluoromethyl and methoxy substituents to the phenylacetylide unit results in color tuning of the phosphorescence energy in these complexes. The bulky diarylamino substituents on the bipyridine ligand showed distinctive electronic properties, resulting in improved hole-transporting characteristics. Solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using these PtII emissive dopants with poly(9-vinylcarbazole) (PVK) as the host. All the devices exhibit promising performances with the best luminance efficiency being up to 20 cd A-1 and the external quantum efficiency reaching 7%.

Constructing solution-processable heavy metal platinum (II) complex with narrowband emission by integrating multiple resonance molecular system

The narrowband emission required by wide color gamut display is an extremely important research topic for any luminescence mechanism, which has made significant progress in traditional fluorescence and thermally activated delayed fluorescence (TADF) based on purely organic compounds, but is far from mature in organometallic complexes. Herein, we propose a feasible molecular design paradigm for constructing the desirable organic electroluminescence (EL) emitter with narrowband emission by integrating an original multiple resonance TADF (MR-TADF) fragment into the classical platinum (II) complex. The solution-processed organic light-emitting diode (OLED) by employing the target model platinum (II) complex BNCPPt as the dopant emitter shows light green emission with a peak of 507 nm and narrow full-width at half-maximum (FWHM) of 35 nm, which achieves a maximum external quantum efficiency (EQE) of 13.5% with very low efficiency roll-off of 4.4% at 1000 cd m−2.

Delayed fluorescence of InP:Mn/ZnS nanocrystals

The photoluminescence properties of ZnS-capped Mn-doped InP nanocrystals are shown to be determined by the high ratio of the radiative rate constants of the host and dopant emission, by the polydispersity-induced inhomogeneous broadening, and by the rapid establishment of thermal equilibrium in the distribution of the excitation between the energy levels of the quantum dot and the dopant ion. Because of the combination of these factors, the resulting photoluminescence includes the delayed host fluorescence and the quenched dopant phosphorescence, both having very broad lifetime distributions.

New green emitters based on push-pull type pyrene substituted cyanopyridones: Design strategies and utilization in organic light-emitting diodes

A novel series of D-A-D type conjugated dyes (Py-CyP1-7) centred on a strongly electron-withdrawing cyanopyridone scaffold (A) linked to highly electron-donating pyrene unit (D) and varied auxiliary donors (D) were designed and synthesized, for applications in green organic light-emitting diodes (OLEDs). All the hybrids were systematically subjected to theoretical, optical, electrochemical, and thermal studies to validate their efficiency in behaving as green emitters. Finally, we employed the dyes as sole and dopant emitters in OLEDs. The OLED with 3 wt % Py-CyP4 in the CBP host shows maximum efficiencies of 14.38 cd A−1, 12.04 lm W−1, and 5.91%.

Synthesis and spectroscopic characterization of Ce0.90Eu0.07Sm0.03O2 phosphors for luminescence-based thermometry applications

Uniform nanoparticles of Eu3+/Sm3+ co-doped CeO2 phosphors were prepared through a hydrothermal method assisted with ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The pH values of the precursor solution were varied to obtain uniform morphology of Eu3+/Sm3+ co-doped CeO2 phosphors and the most uniform morphology of Eu3+/Sm3+ co-doped CeO2 phosphors was obtained at pH 10. The maximum photoluminescence efficiency was observed at 7 mol% of Eu3+ and 3 mol% of Sm3+ ions of Eu3+/Sm3+ co-doped CeO2 phosphors. The emission spectra for Ce0.9Eu0.07Sm0.03O2-δ phosphors consisted of a host (450–560 nm) and dopant (570–700 nm) emissions. The ratio between the intensity of host and dopant emissions showed strong temperature dependence and the variation of intensity ratio was utilized for temperature sensing. Within the studied temperature range (298–523 K), the value of absolute sensor sensitivity for Ce0.9Eu0.07Sm0.03O2-δ phosphors was elevated from 0.0026 to 0.025 K−1. The maximum relative sensor sensitivity of Ce0.9Eu0.07Sm0.03O2-δ phosphors was 2.8% K−1 at 373 K. The high sensor sensitivity and uniform morphology of Ce0.9Eu0.07Sm0.03O2-δ phosphors could be used for luminescence-based thermometry applications.

Mn Doping in Low-Dimensional Perovskites: A Switch for Controlling Dopant and Host Emission

The growth of solid-state photonics relies on the design of highly efficient devices with tunable photoluminescence (PL) based on thermally stable phosphors. In this study, a room-temperature, all-ambient synthesis of Mn-doped hybrid lead halide perovskite phosphors is presented. By applying temperature-dependent (4.2–300 K) steady-state and transient PL measurements, the photophysical pathways of the hybrid system were identified and the carrier recombination processes at play were defined. At higher Mn-doping concentrations (>4%), the excitonic white light host emission nearly disappears, and a bright Mn transition appears at ∼650 nm with a record PL quantum yield of ∼87.4%. The intense sensitized Mn luminescence results from rapid and efficient exciton-to-dopant energy transfer, as evidenced by time-gated and femtosecond fluorescence upconversion measurements. A millisecond PL decay time attributed to the Mn dopant and a microsecond PL decay time associated with the excitonic emission of the host were found, indicating energy and reverse energy transfer in the system. These findings provide unique insights into the chemical tailoring of the Mn-dopant emission by investigating the coupling between the host semiconductor and the dopant ion, a stepping stone toward the development of high-performance solid-state light-emitting diodes and scintillators.

Strong Dopant-Dopant Electronic Coupling in Emissive Codoped Two Dimensional Metal Halide Hybrid.

Multimetallic halide hybrids are attractive for the fundamental understanding of interacting excitons. However, realizing halide hybrids that incorporate multiple heterometal centers has been synthetically challenging. This further limits access to gaining physical insight into the electronic coupling mechanism between the constituent metal halide units. Reported herein is an emissive heterometallic halide hybrid, synthesized by codoping (with Mn2+, Sb3+) a 2D host (C6H22N4CdCl6) hybrid, that shows strong dopant-dopant interaction. Here, C6H22N4Sb0.003Mn0.128Cd0.868Cl6 codoped hybrid shows weak green emission (Sb3+ dopant based) and strong orange emission (Mn2+ dopant based). The observed dominance of the Mn2+ dopant emission, arising due to efficient energy transfer between the distant dopants (Sb3+ → Mn2+), highlights strong dopant-dopant electronic coupling. DFT calculations, supporting the observed dopant-dopant interaction, suggest that the electronic coupling between the dopant units (Mn-Cl; Sb-Cl) is mediated by the 2D networked host structure. This work reports physical insight into the coupling mechanism of interacting excitons in multimetallic halide hybrids synthesized through a codoping strategy.

Multimode‐Responsive Luminescence Smart Platform by Single‐Sm3+‐Doped Phosphors

AbstractMultimode‐responsive luminescence materials play pivotal roles both in understanding the fundamental photophysical processes and fabricating smart devices. To obtain inorganic phosphor‐based multi‐responsive materials, however, triple or even quadruple doping ions or a series of hosts with different compositions are frequently used. In this work, a single‐rare‐earth‐doped phosphor, Sr2YGaO5:Sm3+, with multi‐responsive luminescence is first reported. This single‐Sm3+‐doped phosphor exhibits unique excitation‐wavelength, ultraviolet/X‐ray charging, and thermal stimulated luminescence‐color‐changeable features. Further studies confirm that the multimode‐responsive luminescence of Sr2YGaO5:Sm3+ is attributed to superior optical integration of the host (Sr2YGaO5) and dopant (Sm3+) emissions under specific stimulation conditions. Importantly, this study provides a novel concept for designing inorganic phosphor‐based multifunctional optical materials, which would be conducive to the development of smart platforms.

Understanding and Hindering Ion Migration in Er,Yb:LiLuF4 Core–Shell Nanoparticles for Nanothermometers with Enhanced Photoluminescence

Developing core–shell nanoparticles is a common approach to improve the luminescence performance of nanomaterials, as an inert shell shields the core, which is doped with luminescent ions, from the quenching influence of the environment. Core-only nanoparticles are susceptible to solvent overtones, which can couple with the emissive dopants on the surface and quench their intensity. This is undeniably highly undesired for any luminescence application. It was recently shown by some of us that previously unreported ion migration takes place in 2%Er,18%Yb:LiLuF4@LiLuF4 core–shell nanoparticles, which was proven both with energy-dispersive X-ray (EDX) maps and high-temperature luminescence measurements. These findings lead us to the investigation presented here, which explores in detail how to hinder the migration of Er3+ and Yb3+ ions in LiLuF4 and LiYF4 hosts by implementing an interface region. First, different synthesis routes were explored to see if the chosen approach had any effect on the ion migration process from the doped core into the inert shell in a homogeneous core–shell system. Next, a LiYF4 inert shell was grown around a 2%Er,18%Yb:LiLuF4 core forming a heterogeneous core–shell system. We observed that the heterogeneous 2%Er,18%Yb:LiLuF4@LiYF4 and LiLuF4@2%Er,18%Yb:LiYF4 core–shell combinations showed significantly less ion migration based on EDX maps and high-temperature luminescence measurements exhibiting a behavior similar to the well-studied 2%Er,18%Yb:NaYF4@NaYF4 core–shell structures that, according to previous studies, show no or very little ion migration.

Classic Fluorophores With a Horizontal Alignment for Enhancing Light Outcoupling Efficiency (≈30%) and External Quantum Efficiency (≈7%) of Near Ultraviolet (λmax < 400 nm) Organic Light‐Emitting Diodes

AbstractBased on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λmax of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter (SGIWAXS) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l’ Eclairage coordinates (CIEx,y) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIEx,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (ηout) of the two individual OLEDs are estimated as 31% and 29%, respectively.

Spiral donor-based host materials for highly efficient blue thermally activated delayed fluorescence OLEDs

Spiral donor units have attracted extensive research focuses in designing highly emissive thermally activated delayed fluorescence (TADF) emitters. Herein, to reveal the significance of spiral donor units for constructing highly efficient host materials, several spiral donor-based host materials are developed. With the incorporation of spiral donor, increased intermolecular distance is achieved to reduce the concentration quenching effect of dopant. Moreover, the high triplet energy level of spiral donor can provide an additional energy transfer channel to further improve the device performance. Noteworthy, by connecting spiral donors or conventional carbazole unit with different electron-withdrawing units phenoxathiine 10,10-dioxide (PX) or phenoxathiine (PA), these hosts are given different photophysical properties of TADF, room-temperature phosphorescence (RTP) and conventional fluorescence (CF). The strong electron-withdrawing ability of PX is beneficial to the TADF character of spiral donor-based molecules, while the weak electron-withdrawing ability of PA is beneficial to the RTP property. Consequently, the blue OLEDs with DspiroAc-TRZ as a dopant emitter based on the hosts with TADF characters exhibit higher performance than those with RTP and CF properties, and excellent external quantum efficiency (EQE) of 36.1 % and current efficiency of 84.6 cd/A are achieved in a simple device structure. Furthermore, peak EQEs of 34.0 % and 33.0 % are achieved, when DspiroS-PX and DspiroS-PA hosted DspiroAc-TRZ are used to sensitize blue multi-resonance TADF emitter v-DABNA. Our work may shed new light on designing highly efficient host materials for TADF emitters.

Uniaxial strain tuning of organic molecule single photon sources.

Organic fluorophores are excellent single photon sources, combining high brightness, lifetime-limited linewidths and useful emission wavelengths. A key factor in their performance as photon emitters is their dynamic frequency tunability, which can be used to render the emission from multiple molecules indistinguishable. In this work we demonstrate dynamic tuning of dibenzoterrylene molecules embedded in anthracene crystals through the application of uniaxial strain fields. By bending a piezoelectric strip in two opposite directions in linear steps, we impose an escalating compressive or tensile strain on the molecular crystals, resulting in two opposite dynamic detunings of the dopant dibenzoterrylene emission wavelength. To validate that the tuning mechanism is strain, we performed a similar measurement using an identical strip that was depolarised by annealing in which the tuning was absent. Finally, we simulated the effect of strain on the dopant dibenzoterrylene emission wavelength by combining molecular dynamics and density functional theory techniques to determine the strain tuning rate which matched well with that found experimentally.

Post-synthetic modification of semiconductor nanoparticles can generate lanthanide luminophores and modulate the electronic properties of preformed nanoparticles

Post-synthetic modification of inorganic nanoparticles (NPs) provides a unique lesser synthetically demanding opportunity to access nanomaterials those are oftentimes not directly realizable by conventional synthetic routes. Trivalent lanthanide (Ln3+) incorporated (doped) semiconductor NPs can benefit from individual properties of the NPs and Ln3+ moieties. This work summarizes key outcomes from experiments when (a) ZnS /CdS /CdSe NPs are post-synthetically treated with Ln3+ to generate ZnS/Ln or CdSe/Ln [Ln = Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb] and CdS/Ln [Eu, Tb] NPs, (b) synthetically Tb3+ doped Zn(Tb)S NPs are post-synthetically modified with varying concentration of heavy metals like Pb2+/Cd2+ to generate Zn(Tb)S/M [M = Pb, Cd] NPs, and (c) the pH of Zn(Tb)S NPs aqueous dispersion is varied post-synthetically. Key observations from these experiments include (a) incorporation of Ln in all the post-synthetically prepared CA/Ln NPs, with presence of host sensitized dopant emission in select cases that can be rationalized by a charge trapping mediated dopant emission sensitization processes, (b) existence of rich photophysics in the sub-stoichiometric reactant concentration ratio, and (c) identifying the alteration of surface capping ligand structure as an important variable to control the Ln3+ emission. In summary, these experimental observations provide an easy control of reaction conditions either to generate Ln3+ inorganic NP luminophores or to control their electronic properties by modulating either the NP’s core or surface properties, and are of potential usefulness in various luminescence based applications.