Low Photoluminescence Quantum Yield Research Articles

Lattice Engineering via Transition Metal Ions for Boosting Photoluminescence Quantum Yields of Lead-Free Layered Double Perovskite Nanocrystals.

Lead-free layered double perovskite nanocrystals (NCs), i.e., Cs4M(II)M(III)2Cl12, have recently attracted increasing attention for potential optoelectronic applications due to their low toxicity, direct bandgap nature, and high structural stability. However, the low photoluminescence quantum yield (PLQY, <1%) or even no observed emissions at room temperature have severely blocked the further development of this type of lead-free halide perovskites. Herein, two new layered perovskites, Cs4CoIn2Cl12 (CCoI) and Cs4ZnIn2Cl12 (CZnI), are successfully synthesized at the nanoscale based on previously reported Cs4CuIn2Cl12 (CCuI) NCs, by tuning the M(II) site with different transition metal ions for lattice tailoring. Benefiting from the formation of more self-trapped excitons (STEs) in the distorted lattices, CCoI and CZnI NCs exhibit significantly strengthened STE emissions toward white light compared to the case of almost non-emissive CCuI NCs, by achieving PLQYs of 4.3% and 11.4% respectively. The theoretical and experimental results hint that CCoI and CZnI NCs possess much lower lattice deformation energies than that of reference CCuI NCs, which are favorable for the recombination of as-formed STEs in a radiative way. This work proposes an effective strategy of lattice engineering to boost the photoluminescent properties of lead-free layered double perovskites for their future warm white light-emitting applications.

Enhancing luminescence of AF2: Ln3+ (A = Ca, Sr; Ln = Eu, Tb) by the use of carbon dots

Lanthanide ions-doped fluoride nanocrystals have excellent application prospect. However, low photoluminescence quantum yield (PLQY) is usually along with lanthanide ions-doped fluoride nanocrystals owing to their low molar absorptivity and narrow absorption band. In order to increase the absorption cross section of Ln3+ in fluoride nanocrystals, a facile synthesis strategy to enhance luminescence of AF2: Ln3+ (A = Ca, Sr; Ln = Eu, Tb) by the use of carbon dots (CDs) has been developed in this work. A series of characterizations including TEM, XRD, FTIR and XPS demonstrated that the CDs have been successfully combined with the surface of AF2: Ln3+ nanocrystals. The combination of CDs has little influence on the microstructure and phase structure of AF2: Ln3+, and CDs@AF2: Ln3+ nanocrystals have uniform and regular shape with cubic phase. CDs are used as a broadband sensitizer and lead to the broadband excitation of Ln3+, resulting in the enhancement around 10-fold of Ln3+ luminescence emission in AF2: Ln3+ nanocrystals after CDs combination. The corresponding PLQY increases almost three times, and the luminescence enhancement mechanism by combining CDs is proposed. In addition, the CDs@AF2: Ln3+ nanocrystals are used to prepare CDs@AF2: Ln3+/PVA films, which exhibits excellent luminescence properties under the excitation of UV light. This work provides a superior method for enhancing the luminescence properties of lanthanide ions-doped nanocomposites and demonstrates practical potential as promising candidates for light-converting thin films.

High-Efficiency and Stable Colloidal One-Dimensional Core/Shell Nanorod Light-Emitting Diodes.

Anisotropic nanocrystals such as nanorods (NRs) display unique linearly polarized emission, which is expected to break the external quantum efficiency (EQE) limit of quantum dot-based light-emitting diodes (LEDs). However, the progress in achieving a higher EQE using NRs encounters several challenges, primarily involving a low photoluminescence quantum yield (PLQY) of NRs and imbalanced charge injection in NR-LEDs. In this work, we investigated NR-LEDs based on CdSe/CdZnS/ZnS rod-in-rod NRs with a high PLQY and higher linear polarization compared to those of dot-in-rod NRs. The balanced charge injection is achieved using ZnMgO nanoparticles as the electron transport layer and poly-TPD {poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine]} as the hole transport layer. Therefore, the NR-LEDs exhibit a maximum EQE of 21.5% and a maximum luminance of >120 000 cd/m2 owing to the high level of in-plane transitions with a dipole moment of 90%. The NR-LEDs also have greatly inhibited droop in EQE under a high current density as well as outstanding operation lifetime and cycle stability.

Z-Type Ligand Enables Efficient and Stable Deep-Blue Perovskite Light-Emitting Diodes.

During the synthesis of deep-blue perovskite quantum dots (PQDs), they generally emerge as a two-dimensional byproduct with poor yield and low photoluminescence quantum yield (PLQY) due to amine ligand enrichment-induced abundant surface defects. Herein, we provide a colloidal synthesis method to prepare deep-blue CsPbBr3 PQDs in a green nontoxic solvent via strategic Z-type ligand engineering. Z-type ligands of zinc octanoate enable the formation of robust coordination bonds with surface bromide ions of PQDs, maintaining acid-base equilibrium and reducing excess amine enrichment on the PQDs surface. Consequently, homogeneous and monodispersed PQDs with improved PLQY of 73% are successfully synthesized, achieving efficient deep-blue LEDs with a peak EQE of 5.46%, a maximum luminance of 847.6 cd/m2, and an operational half-lifetime of 14 min. The devices exhibit color coordinates of (0.137, 0.049), closely approximating the Rec. 2020 blue standard. Our work offers a potentially eco-friendly and viable route for realizing high-performance LEDs in the deep-blue region.

PVP Passivated δ-CsPbI3: Vacancy Induced Visible-Light Absorption and Efficient Photocatalysis.

The aqueous instability of halide perovskite seriously hinders its direct application in water as a potential photocatalyst. Here, we prepared a new type of polyvinylpyrrolidone (PVP) passivated δ-CsPbI3 (δ-CsPbI3@PVP) microcrystal by a facile method. This material can be uniformly dispersed in water and stably maintain its crystal structure for a long time, breaking through the bottleneck of halide perovskite photocatalysis in water. Under visible light, δ-CsPbI3@PVP can almost completely photodegrade organic dyes (including Rhodamine B, methylene blue, and crystal violet) in only 20 min. The efficient photocatalytic activity is attributed to the enhanced visible light absorption arising from PbI2 defects in δ-CsPbI3@PVP and the intrinsic low photoluminescence quantum yield of δ-CsPbI3, which induces efficient light absorption and photocatalytic activity. We highlight δ-CsPbI3@PVP as an effective aqueous photocatalyst, and this study provides new insights into how to exploit the potential of halide perovskite in photocatalytic applications.

Modified t-butyl in tetradentate platinum (II) complexes enables exceptional lifetime for blue-phosphorescent organic light-emitting diodes

In blue phosphorescent dopants, the tetradentate platinum(II) complex is a promising material showing high efficiency and stability in devices. However, metal-metal-to-ligand charge transfer (MMLCT) formation leads to low photo-luminescence quantum yields (PLQYs), wide spectra, and intermolecular interaction. To suppress MMLCT, PtON-tb-TTB and PtON-tb-DTB are designed using theoretical simulation by modifying t-butyl in PtON-TBBI. Both materials effectively suppress MMLCT and exhibit high PLQYs of 99% and 78% in 5 wt% doped film, respectively. The PtON-tb-TTB and PtON-tb-DTB devices have maximum external quantum efficiencies of 26.3% and 20.9%, respectively. Additionally, the PtON-tb-DTB device has an extended lifetime of 169.3 h with an initial luminescence of 1200 nit, which is 8.5 times greater than the PtON-TBBI device. Extended lifetime because of suppressed MMLCT and smaller displacement between the lowest triplet and triplet metal-centered states compared to other dopants. The study provides an effective approach to designing platinum(II) complexes for long device lifetimes.

High‐Performance White Emission from Cu‐Based Perovskite Compound

AbstractThe white emissions based on lead‐free perovskites with broadband emission due to self‐trapped excitons (STEs) are considered as an ideal candidate for next‐generation white light‐emitting diodes (WLEDs). Recently, copper‐based halide perovskites Cs3Cu2I5@CsCu2I3 composites films with a high color‐rendering index (CRI) have been developed for WLEDs. However, the Cs3Cu2I5@CsCu2I3 composites generally exhibit a relatively low photoluminescence quantum yield (PLQY). Herein, a high PLQY up to 86.75% copper‐based perovskite Gua3Cu2I5 (Gua = guanidine) films with a broadband strong yellow STEs emission centered at 544 nm is synthesized. By combining with efficient blue STEs emission Cs3Cu2I5 component via composition engineering of Cs3Cu2I5@Gua3Cu2I5, a high PLQY of up to 96.1% is achieved on the white emission composites films. Moreover, a high CRI of 93 WLEDs is achieved by integrating Cs3Cu2I5@Gua3Cu2I5 composites film onto a UV LED chip. These findings provide a simple and effective strategy for designing highly efficient white light‐emitting diodes.

Harnessing the Synergetic Effects of Ag, Mn Dopants in Eco-Friendly Ultraviolet Selective Quantum Dots for Luminescent Solar Concentrators.

Quantum dots (QDs) are promising building blocks for luminescent solar concentrators (LSCs), yet most QD-based LSCs suffer from toxic metal composition and color tinting. UV-selective harvesting QDs can enable visible transparency, but their development is restricted by large reabsorption losses and low photoluminescence quantum yield (PLQY). The developed here Ag, Mn: ZnInS2/ZnS QDs show a high PLQY of 53% due to the passivating effect of ZnS shell. These QDs selectively absorb UV light and emit orange-red light with a large Stokes shift of 180nm. A LSC of 5×5×0.2cm3, fabricated using a poly(lauryl methacrylate) (PLMA) as a matrix, maintains 87% of integrated PL after 7h of UV exposure. The QD-PLMA achieved 90.7% average visible transparency (AVT) and a color rendering index (CRI) of 95.8, which is close to plain PLMA (AVT=90.8%; CRI=99.5), yielding excellent visible light transparency. Incorporating Si-PVs at LSC edges, the Ag, Mn: ZIS/ZnS QD-LSC achieved an optical efficiency of 1.42%, ranking competitively among high-performing UV-harvesting LSCs.

Enhancing the Photoluminescence and Electroluminescence of Graphitic Carbon Nitride via Atomic and Molecular Co-modification.

Graphitic carbon nitride (g-CN) materials exhibit attractive optoelectronic physical properties; however, their low photoluminescence quantum yields (PLQYs) limit their applications in luminescent devices. Here, boron-doped aromatic carbon nitride (B-PhCNx) was synthesized for the first time via direct thermal polymerization of 2,4-diamino-6-phenyl-1,3,5-triazine and boric acid. The impact of B doping and phenyl modifying on the structural and optical characteristics of the samples was investigated in detail. The highest PLQY of 40.7% was achieved in B-PhCN20, which is 6.8 times that of pristine carbon nitride (p-CN). The B-PhCN20-based light-emitting diode demonstrates a maximum luminance of 1494 cd m-2 and a maximum external quantum efficiency of 1.03%, which are 3.5 and 4.9 times that of the p-CN-based device, respectively. Our findings will provide a reference for rationally designing low-cost and high-performance carbon-nitride-based optoelectronic devices.

Introduction of a Chiral Biphenanthrene-Diol Unit to Achieve Circularly Polarized Thermally Activated Delayed Fluorescence.

Circularly polarized luminescence (CPL) materials are promising candidates for future display technology. However, such highly efficient emitters suffer from the issues of difficult chiral separation and low photoluminescence quantum yield (PLQY). In this work, the chiral 4,4'-biphenanthrene-3,3'-diol (BIPOL) unit was introduced into a thermally activated delayed fluorescence (TADF) framework for the first time. We presented two series of enantiomers, R/S-o-DCzBPNCN and R/S-p-DCzBPNCN, and the synthesis of enantiopure BIPOL can be prepared via normal column chromatography. Notably, o-DCzBPNCN showed narrow singlet-triplet gap of 0.05 eV, efficient TADF, and high PLQYs of 82 % in doped films. In addition, R/S-o-DCzBPNCN exhibited high luminescence dissymmetry factor (gPL ) values of -1.94×10-2 /+1.91×10-2 in doped films. The strategy of BIPOL introduction offers a new approach to organic emitters with stereospecific synthesis, TADF, and chiroptical properties.

Mild synthesis of ultra-bright carbon dots with solvatochromism for rapid lipid droplet monitoring in varied physiological processes.

Lipid droplets (LDs) participating in various cellular activities and are increasingly being emphasized. Fluorescence imaging provides powerful tool for dynamic tracking of LDs, however, most current LDs probes remain inconsistent performance such as low Photoluminescence Quantum Yield (PLQY), poor photostability and tedious washing procedures. Herein, a novel yellow-emissive carbon dot (OT-CD) has been synthesized conveniently with high PLQY up to 90%. Besides, OT-CD exhibits remarkable amphiphilicity and solvatochromic property with lipid-water partition coefficient higher than 2, which is much higher than most LDs probes. These characters enable OT-CD high brightness, stable and wash-free LDs probing, and feasible for in vivo imaging. Then, detailed observation of LDs morphological and polarity variation dynamically in different cellular states were recorded, including ferroptosis and other diseases processes. Furthermore, fast whole imaging of zebrafish and identified LD enrichment in injured liver indicate its further feasibility for in vivo application. In contrast to the reported studies to date, this approach provides a versatile conventional synthesis system for high-performance LDs targeting probes, combing the advantages of easy and high-yield production, as well as robust brightness and stability for long-term imaging, facilitating investigations into organelle interactions and LD-associated diseases.

Photoluminescence quantum yield of carbon dots: emission due to multiple centers versus excitonic emission.

Carbon dots (CDs) are recognized as promising fluorescent nanomaterials with bright emission and large variations of photoluminescence quantum yield (PLQY). However, there is still no unique approach for explanation of mechanisms and recipes for synthetic procedures/chemical composition of CDs responsible for the enhancement of PLQY. Here, we compare photophysical behavior and PLQY of two types of CDs synthesized by different routes, leading to the different extent of oxidation and composition. The first type of CDs represents a conjugated carbon system oxidized by F, N and O heteroatoms, whereas the second type represents a non-conjugated carbon system oxidized by oxygen. Photophysical data, photoemission spectroscopy and microscopy data yield the suggestion that in the first case, a structure with a distinct carbon core and highly oxidized electron-accepting shell is formed. This leads to the excitonic type non-tunable emission with single-exponent decay and high PLQY with a strong dependence on the solvent polarity, being as high as 93% in dioxane and as low as 30% in aqueous medium, but which is vulnerable to photobleaching. In the second case, the oxidized CDs do not indicate a clear core-shell structure and show poor solvatochromism, negligible photobleaching, low PLQY varying in the range of 0.7-2.3% depending on the solvent used, and tunable emission with multi-exponent decay, which can be described by the model of multiple emission centers acting through a clustering-triggered emission mechanism. The obtained results lead to a strategy that allows one to design carbon nanomaterials with principally different PLQYs that differ by orders of magnitude.

Defect Engineering of 2D Semiconductors for Dual Control of Emission and Carrier Polarity.

2D transition metal dichalcogenides (TMDCs) are considered as promising materials in post-Moore technology. However, the low photoluminescence quantum yields (PLQY) and single carrier polarity due to the inevitable defects during material preparation are great obstacles to their practical applications. Here, an extraordinary defect engineering strategy is reported based on first-principles calculations and realize it experimentally on WS2 monolayers by doping with IIIA atoms. The doped samples with large sizes possess both giant PLQY enhancement and effective carrier polarity modulation. Surprisingly, the high PL emission maintained even after one year under ambient environment. Moreover, the constructed p-n homojunctions shows high rectification ratio (≈2200), ultrafast response times and excellent stability. Meanwhile, the doping strategy is universally applicable to other TMDCs and dopants. This smart defect engineering strategy not only provides a general scheme to eliminate the negative influence of defects, but also utilize them to achieve desired optoelectronic properties for multifunctional applications.

Enhanced Horizontal Dipole Orientation by Novel Penta-Helicene Anthracene-Based Host for Efficient Blue Fluorescent OLEDs.

Due to the relatively low photoluminescence quantum yield (PLQY) and horizontal dipole orientation of doped films, anthracene-based fluorescent organic light-emitting diodes (F-OLEDs) have faced a great challenge to achieve high external quantum efficiency (EQE). Herein, a novel approach is introduced by incorporating penta-helicene into anthracene, presented as linear-shaped 3-(4-(10-phenylanthracen-9-yl)phenyl)dibenzo[c,g]phenanthrene (BABH) and 3-(4-(10-(naphthalen-2-yl)anthracen-9-yl)phenyl)dibenzo[c,g]phenanthrene (NABH). These blue hosts exhibit minimal intermolecular overlap of π-π stacking, effectively suppressing excimer formation, which facilitates the effective transfer of singlet energy to the fluorescent dopant for PLQY as high as 90%. Additionally, the as-obtained two hosts of BABH and NABH have effectively demonstrated major horizontal components transition dipole moments (TDM) and high thermal stability with glass transitional temperature (Tg ) surpassing 188°C, enhancing the horizontal dipole orientation of their doped films to be 89% and 93%, respectively. The OLEDs based on BABH and NABH exhibit excellent EQE of 10.5% and 12.4% at 462nm and device lifetime up to 90% of the initial luminance over 4500h at 100cdm-2 , which has firmly established them as among the most efficient blue F-OLEDs based on anthracene to date to the best knowledge. This work provides an instructive strategy to design an effective host for highly efficient and stable F-OLEDs.

Tunable dual-emission of Sb3+, Ho3+ Co-doped Cs2NaScCl6 single crystals for light-emitting diodes

Lead-free halide double perovskites are considered as one of the most promising materials in optoelectronic devices, such as solar cells, photodetectors, and light-emitting diodes (LEDs), due to their environmental friendliness and chemical stability. However, the extremely low photoluminescence quantum yield (PLQY) of self-trapped excitons (STEs) emission from lead-free halide double perovskites impedes their applications. Herein, Sb3+ ions were doped into rare-earth-based double perovskite Cs2NaScCl6 single crystals (SCs), resulting in a large enhancement of PLQY from 12.57% to 87.37%. Moreover, by co-doping Sb3+ and Ho3+ into Cs2NaScCl6 SCs, the emission color can be tuned from blue to red, due to an efficient energy transfer from STEs to Ho3+ ions. Finally, the synthesized sample was used in multicolor LED, which exhibited excellent stability and optical properties. This work not only provides a new strategy for improving the optical properties of Cs2NaScCl6 SCs, but also suggests its potential application in multicolor LEDs.

Near-Infrared Emission of Ag+ Doped CuInSe2 Quantum Dots

Copper-indium-selenide (CISe) quantum dots (QDs) are a class of appealing materials due to their near-infrared (NIR) photoluminescence (PL) and as a non-toxic alternative to lead and cadmium-based QDs. To improve the low photoluminescence quantum yield (PLQY) of CISe core QDs, the zinc sulfide (ZnS) shell was grown to passivate surface defect states on the CISe core. CISe/ZnS core-shell QDs were synthesized with tetrahedral structure and chalcopyrite phase, resulting in an emission wavelength of 992 nm and a PLQY of 90%. Additionally, Ag2+ was doped into the CISe core to redshift the emission wavelength. The combination of electrons in the conduction band and holes in the trap state formed by Ag2+ led to light emission and a red-shifted emission wavelength. By tuning the stoichiometry and shelling time, Ag-doped CISe/ZnS core-shell QDs were successfully synthesized with a PLQY of 18% at an emission wavelength of 1200 nm. This wavelength falls in the NIR-II range, characterized by minimum absorption, biological autofluorescence, reduced scattering, and deep tissue penetration. The tunable emission and high luminescent CISe QDs have great potential in biological labeling, sensing and optoelectronics applications. Figure 1

In situ precipitation of high efficiency and high thermostability CsPbBr3 quantum dots in borosilicate glass for wide color gamut display

In situ precipitation of CsPbBr3 quantum dots (QDs) in glass is considered as one of the effective methods to overcome its instability and to achieve practical applications. However, it still faces the great challenges of low photoluminescence quantum yield (PLQY), poor thermostability and photostability at present. Herein, we successfully prepared CsPbBr3 QDs in situ within a well-designed glass matrix (CsPbBr3 QDs@glass), which exhibits symmetric narrowband emission at 523 nm with a full width at half maximum (FWHM) of 25 nm, giving a PLQY of up to 52.15 % under 455 nm excitation. Meanwhile, it can keep 45.25 % of the initial luminescence intensity at 373 K, better than that of most reported CsPbBr3 QDs@glass materials. As a demonstration of a conceptual application, a white LED backlight strip was fabricated at home by encapsulating CsPbBr3 QDs@glass composite and K2SiF6:Mn4+ red phosphor on blue chips with silicone, achieving a wide color gamut of 128.6 % and 95.8 % of NTSC and Rec. 2020 color gamut, respectively. The assembled CsPbBr3 QDs@glass-based LCD screen exhibits excellent color reproduction and color saturation. All these results demonstrate that this CsPbBr3 QDs@glass composite material is a promising green emitter for wide color gamut LCD display.

Enhancing the quantum yield and stability of CsPbBr3 quantum dots with zwitterionic ligand post-treatment

The poor stability and low photoluminescence quantum yield (PLQY) of halide perovskite quantum dots (QDs) have been major challenges for their future practical application. Ligand engineering has been demonstrated as an effective approach for enhancing both stability and PLQY. Herein, we introduce a zwitterionic ligand, specifically N-tetradecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (TDPS), to synthesize stable CsPbBr3 QDs by ligand post-treatment. The as-prepared TDPS-QDs exhibited an exceptional PLQY of 86.5 % and superior colloidal stability when exposed to UV light, heat, and polar solvents, owing to surface defect passivation and strong affinity to the surfaces. The PL intensity of TDPS-QDs maintains approximately 68 % (120 min) and 103 % (48 h) of its initial emission intensity under continuous irradiation or heat, respectively, whereas OA-QDs (pristine CsPbBr3 QDs) undergo greater quenching within a shorter period. The findings highlight the potential for TDPS ligand modification to simultaneously improve the QY and stability, thus opening novel avenues for future applications involving CsPbBr3 QDs.

Near-Infrared Nanophosphors Based on CuInSe2 Quantum Dots with Near-Unity Photoluminescence Quantum Yield for Micro-LEDs Applications.

Highly efficient near-infrared (NIR) luminescent nanomaterials are urgently required for portable mini or micro phosphors-converted light-emitting diodes (pc-LEDs). However, most existing NIR-emitting phosphors are generally restricted by their low photoluminescence (PL) quantum yield (QY) or large particle size. Herein, a kind of highly efficient NIR nanophosphors is developed based on copper indium selenide quantum dots (CISe QDs). The PL peak of these QDs can be exquisitely manipulated from 750 to 1150nm by altering the stoichiometry of Cu/In and doping with Zn2+ . Their absolute PLQY can be significantly improved from 28.6% to 92.8% via coating a ZnSe shell. By combining the phosphors with a commercial blue chip, an NIR pc-LED is fabricated with remarkable photostability and a record-high radiant flux of 88.7 mW@350mA among the Pb/Cd-free QDs-based NIR pc-LEDs. Particularly, such QDs-based nanophosphors acted as excellent luminescence converter for NIR micro-LEDs with microarray diameters below 5µm, which significantly exceeds the resolutions of current commercial inkjet display pixels. The findings may open new avenues for the exploration of highly efficient NIR micro-LEDs in a variety of applications.

Reduction of Non‐Radiative Losses in Trap‐Free Organic Light‐Emitting Diodes by Dilution with A Large Bandgap Host

AbstractThe emitter 9,9′,9′'‐(5‐(4,6‐diphenyl‐1,3,5‐triazin‐2‐yl)benzene‐1,2,3‐triyl)tris(9H‐carbazole) (3CzTRZ) seems an ideal candidate for efficient single‐layer blue organic light‐emitting diodes (OLEDs). It combines trap‐free electron and hole transport with thermally activated delayed fluorescence (TADF) for triplet harvesting. However, in spite of the absence of charge trapping defects, neat films of 3CzTRZ suffer from a low photoluminescence quantum yield (PLQY) of only 40%. Time‐resolved photoluminescence measurements reveal that the low PLQY results from the fact that next to fast intersystem crossing the rate for reverse intersystem crossing is very slow and nearly similar to the rate of non‐radiative recombination of triplet excitons to the ground state. This loss process of non‐radiative triplet decay is even more pronounced in OLEDs due to the 75% direct triplet‐exciton formation, resulting in a low external quantum efficiency (EQE) of 4.5%. By diluting 3CzTRZ in a large bandgap host, the triplet lifetime is increased by at least an order of magnitude, resulting in an enhanced PLQY of 70% and a more than three‐fold enhancement of the EQE to 15% in a single‐layer blue OLED. Device simulations confirm that the increased EQE can be ascribed to an elongated triplet lifetime upon dilution of the emitter in a host matrix.