High-efficiency upconversion luminescence in UCNPs/CsPbBr3 nanocomposites enhanced by silver nanoparticles.

Upconversion nanocomposites with multiple light-emitting centers have attracted great attention as functional materials, but their low efficiency limits their further applications. Herein, a novel, to the best of our knowledge, system for nanocomposites consisting of upconversion nanoparticles (UCNPs) and perovskite quantum dots (PeQDs) assembled with Ag nanoparticles (NPs) is proposed. Upconversion luminescence (UCL) operation from PeQDs is triggered by near-infrared (NIR) sensitization through Förster resonance energy transfer (FRET) and photon reabsorption (PR). Especially, the photoluminescence (PL) emission efficiency is found to be significantly enhanced due to the increased energy transfer efficiency and radiative decay rate in the UCNPs/CsPbBr3 nanocomposites. The results offer new opportunities to improve the UCL properties of perovskites and open new development in the fields of LED lighting, solar cells, biomedicine, and so on.

Multi-color UCNPs/CsPb(Br1-xIx)3 for upconversion luminescence and dual-modal anticounterfeiting.

Advanced hybrid materials have attracted extensive attention in optoelectronics and photonics application due to their unique and excellent properties. Here, the multicolor upconversion luminescence properties of the hybrid materials composed of CsPbX3(X = Br/I) perovskite quantum dots and upconversion nanoparticles (UCNPs, core-shell NaYF4:25%Yb3+,0.5%Tm3+@NaYF4) is reported, achieving the upconversion luminescence with stable and bright of CsPbX3 perovskite quantum dots under 980 nm excitation. Compared with the nonlinear upconversion of multi-photon absorption in perovskite, UCNPs/CsPbX3 achieves lower power density excitation by using the UCNPs as the physical energy transfer level, meeting the demand for multi-color upconversion luminescence in optical applications. Also, the UCNPs/CsPbX3 combined with ultraviolet curable resin (UVCR) shows excellent water and air stability, which can be employed as multicolor fluorescent ink for screen printing security labels. Through the conversion strategy, the message of the security labels can be encrypted and decrypted by using UV light and a 980 nm continuous wave excitation laser as a switch, which greatly improves the difficulty of forgery. These findings provide a general method to stimulate photon upconversion and improve the stability of perovskite nanocrystals, which will be better applied in the field of anti-counterfeiting.

Site-selective occupation, optical spectrum regulation and photoluminescence property investigation of Eu2+-activated blue light-excited yellow-orange emitting phosphors.

We report yellow-orange emitting phosphors Sr9-xCaxMg1.5(PO4)7:0.05Eu2+ (SCxMPO:Eu2+, x = 0.5-2.5) and Sr9-yBayMg1.5(PO4)7:0.05Eu2+ (SByMPO:Eu2+, y = 0.5-3.0) with broad emission bands (450-800 nm). All these phosphors can be excited efficiently by blue light and n-UV light. Their crystal structure, photoluminescence spectra, fluorescence decay curves and thermal stability were investigated in detail. As doping concentrations of Ca2+ or Ba2+ increase, Eu2+ emitting centers will selectively occupy different Sr2+ sites, thus leading to the regulation of optical spectra of SCxMPO:Eu2+ and SByMPO:Eu2+. Accordingly, the emission colors of SCxMPO:Eu2+ and SByMPO:Eu2+ samples can gradually turn from yellow to orange when excited using 460 nm blue light. And the emission colors of a given sample can also be varied under different excitations because there are three kinds of emitting centers in SCxMPO:Eu2+ and SByMPO:Eu2+. In addition, introducing Ca2+ and Ba2+ can enhance the thermal stability of the phosphors obviously, and overall, the thermal stability of SByMPO:Eu2+ is better than that of SCxMPO:Eu2+. We chose SB2.5MPO:zEu2+ as an example to further investigate its photoluminescence properties, and found that the optimal doping concentration of Eu2+ is 0.08, and dipole-quadrupole interaction is dominated in the concentration quenching mechanism. Furthermore, high-quality warm white light can be obtained by two ways: (a) 470 nm blue LED chip + SC1.5MPO:Eu2+ [CCT = 3639 K, Ra = 82.21] and (b) 470 nm blue LED chip + SB2.5MPO:Eu2+ and YAG:Ce3+ [CCT = 4284 K, Ra = 86.69]. The excellent performances indicate that SCxMPO:Eu2+ and SByMPO:Eu2+ are attractive candidates for warm WLEDs.

STED microscopy reveals in-situ photoluminescence properties of single nanostructures in densely perovskite thin films.

All-inorganic perovskite nanomaterials have attracted much attention recently due to their prominent optical performance and potential application for optoelectronic devices. The carriers dynamics of all-inorganic perovskites has been the research focus because the understanding of carriers dynamics process is of critical importance for improving the fluorescence conversion efficiency. While photophysical properties of excited carrier are usually measured at the macroscopic scale, it is necessary to probe the in-situ dynamics process at the nanometer scale and gain deep insights into the photophysical mechanisms and their localized dependence on the thin-film nanostructures. Stimulated emission depletion (STED) nanoscopy with super-resolution beyond the diffraction limit can directly provide explicit information at a single particle level or nanometer scale. Through this unique technique, we firstly study the in-situ dynamics process of single CsPbBr3 nanocrystals(NCs) and nanostructures embedded inside high-dense samples. Our findings reveal the different physical mechanisms of PL blinking and antibunching for single CsPbBr3 NCs and nanostructures that correlate with thin-film nanostructural features (e.g. defects, grain boundaries and carrier mobility). The insights gained into such nanostructure-localized physical mechanisms are critically important for further improving the material quality and its corresponding device performance.

Luminescence property improvement and controllable color regulation of a novel Bi3+ doped Ca2Ta2O7 green phosphor through charge compensation engineering and energy transfer.

In pursuit of warm WLEDs, exploration of novel phosphors and regulation of the existing phosphors are the two approaches usually used in the luminescent material field. In this work, we prepared green Ca2Ta2O7:Bi3+ phosphors firstly and investigated their properties in detail. The as-prepared Ca2Ta2O7:Bi3+ exhibits intense green emission in the 450-580 nm range under UV excitation, which matches well with the UV chip and can efficiently avoid the re-absorption problem. The improvement in the emission intensity and thermal stability of the phosphor was achieved using different charge compensation methods including codoping alkali metal ions (Li+, Na+, and K+), creating a cation vacancy, and host co-substitution (Ca2+ + Ta5+ → Bi3+ + Si4+, Ca2+ + Ta5+ → Bi3+ + Ge4+). Through systematic research, the emission intensity at room temperature was improved 2.1 times and the thermal stability was improved 2.9 times at 200 °C. By coating the prepared green sample with other commercial phosphors on the UV chip, warm WLEDs with Ra being 91.1 and CCT being 3990 K were obtained. Moreover, taking the Bi3+ → Eu3+ energy transfer strategy, the emitting color of the phosphor was tuned and yellow emitting phosphor was obtained. Our study indicates that Bi3+ doped Ca2Ta2O7 might be a potential UV excited green phosphor for WLEDs. The charge compensation methods and the Bi3+ → Eu3+ energy transfer approach are valuable ways to improve and adjust the luminescence properties, which can further derivate a series of novel phosphors for improving the quality of WLED devices.

Efficient green phosphor realized by Ce3+→Tb3+ energy transfer in Li3Sc2(PO4)3 for ultraviolet white light-emitting diodes.

A series of Ce3+/Tb3+ doped Li3Sc2(PO4)3 phosphors has been obtained using high temperature solid state reactions. Density functional theory (DFT) calculations using the CASTEP module have given an insight into the bandgap and electronic structures of the hosts. The phase formation and the crystal structure of the prepared samples were verified using X-ray diffraction and Rietveld structure refinement analysis. Samples singly doped with Ce3+ ions had an intense emission centered at 350 nm under UV light irradiation, while samples singly doped with Tb3+ ions exhibited a typical green emission under 230 nm irradiation. Efficient Ce3+→Tb3+ energy transfer can cause the Li3Sc2(PO4)3:Ce3+,Tb3+ samples to have an intense green emission at very low Tb3+ concentrations under 285 nm excitation, making Li3Sc2(PO4)3:Ce3+,Tb3+ an efficient UV-excited green phosphor. The mechanism and critical distance for Ce3+→Tb3+ energy transfer in the phosphor were determined by detailed luminescence decay curve analysis utilizing the I-H model. Moreover, a WLED device was fabricated using our prepared green phosphor.

Potential color tunable Sr3LaNa(PO4)3F:Eu2+/Tb3+/Mn2+ phosphor induced by Eu2+ → Tb3+ and Tb3+ → Mn2+ energy transfer for WLEDs.

Color tunable Sr3LaNa(PO4)3F:Eu2+,Tb3+ and Sr3LaNa(PO4)3F:Tb3+,Mn2+ phosphors were prepared by a high temperature solid state reaction. The crystal structure, luminescence properties, and energy transfer mechanism of the samples were investigated in detail. The Eu2+ doped phosphors can be efficiently excited in the range from 250 to 410 nm, which matches well with the commercial n-UV LED chips. Utilizing the energy transfer from Eu2+ to Tb3+ ions, tunable colors from blue to green were obtained under the irradiation of 405 nm. The mechanism of the Eu2+ → Tb3+ energy transfer was demonstrated to be a dipole-quadrupole interaction in terms of the experimental results and analysis of the photoluminescence spectra and decay curves of the phosphors. Moreover, the thermal stability and quantum efficiency of the Eu2+ and Tb3+ co-doped phosphors were studied. For the Sr3LaNa(PO4)3F:Tb3+,Mn2+ samples, tunable green-orange emissions were obtained by changing the relative ratio of Tb3+ and Mn2+ ions under 230 nm irradiation. The investigation results suggest that color tunable phosphors with potential for WLEDs were obtained utilizing the energy transfer process.

Broadband Yellowish-Green Emitting Ba4Gd3Na3(PO4)6F2:Eu(2+) Phosphor: Structure Refinement, Energy Transfer, and Thermal Stability.

A series of Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphors with a broad emitting band have been synthesized by a traditional solid state reaction. The crystal structural and photoluminescence properties of Ba4Gd3Na3(PO4)6F2:Eu(2+) are investigated. The different crystallographic sites of Eu(2+) in Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphors have been verified by means of their photoluminescence (PL) properties and decay times. Energy transfer between Eu(2+) ions, analyzed by excitation, emission, and PL decay behavior, has been indicated to be a dipole-dipole mechanism. Moreover, the luminescence quantum yield as well as the thermal stability of the Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphor have been investigated systematically. The as-prepared Ba4Gd3Na3(PO4)6F2:Eu(2+) phosphor can act as a promising candidate for n-UV convertible white LEDs.

Topotactic Transformation Route to Monodisperse ß-NaYF4:Ln(3+) Microcrystals with Luminescence Properties.

A novel nonorganic wet route for direct synthesis of uniform hexagonal ß-NaYF4:Ln(3+) (Ln = Eu, Tb, Ce/Tb, Yb/Er, and Yb/Tm) microcrystals with various morphologies has been developed wherein the intermediate routine cubic-hexagonal (α → ß) phase transfer process was avoided. The morphology can be effectively tuned into hexagonal disc, prism, and novel hierarchical architectures by systematically fine manipulating the Na2CO3/F(-) feeding ratio. It has been found that the routine α → ß phase transfer for NaYF4 was not detected during the growth, while NaY(CO3)F2 emerged in the initial reaction stage and fast transformed into ß-NaYF4 via a novel topotactic transformation behavior. Detailed structural analysis showed that ß-NaYF4 preferred the [001] epitaxial growth direction of NaY(CO3)F2 due to the structural matching of [001]NaY(CO3)F2//[0001]ß-NaYF4. Besides, the potential application of the as-prepared products as phosphors is emphasized by demonstrating multicolor emissions including downconversion, upconversion, and energy transfer (Ce-Tb) process by lanthanides doping.

Synthesis, structure, and photoluminescence properties of novel KBaSc2 (PO4 )3 :Ce(3+) /Eu(2+) /Tb(3+) phosphors for white-light-emitting diodes.

A series of novel KBaSc2 (PO4 )3 :Ce(3+) /Eu(2+) /Tb(3+) phosphors are prepared using a solid-state reaction. X-ray diffraction analysis and Rietveld structure refinement are used to check the phase purity and crystal structure of the prepared samples. Ce(3+) - and Eu(2+) -doped phosphors both have broad excitation and emission bands, owing to the spin- and orbital-allowed electron transition between the 4f and 5d energy levels. By co-doping the KBaSc2 (PO4 )3 :Eu(2+) and KBaSc2 (PO4 )3 :Ce(3+) phosphors with Tb(3+) ions, tunable colors from blue to green can be obtained. The critical distance between the Eu(2+) and Tb(3+) ions is calculated by a concentration quenching method and the energy-transfer mechanism for Eu(2+) →Tb(3+) is studied by utilizing the Inokuti-Hirayama model. In addition, the quantum efficiencies of the prepared samples are measured. The results indicate that KBaSc2 (PO4 )3 :Eu(2+) ,Tb(3+) and KBaSc2 (PO4 )3 :Ce(3+) ,Tb(3+) phosphors might have potential applications in UV-excited white-light-emitting diodes.

Luminescence properties of Ca2 Ga2 SiO7 :RE phosphors for UV white-light-emitting diodes.

A series of Eu(2+) -, Ce(3+) -, and Tb(3+) -doped Ca2 Ga2 SiO7 phosphors is synthesized by using a high-temperature solid-state reaction. The powder X-ray diffraction and structure refinement data indicate that our prepared phosphors are single phased and the phosphor crystalizes in a tetrahedral system with the ${P\bar 42m}$ (113) space group. The Eu(2+) - and Ce(3+) -doped phosphors both have broad excitation bands, which match well with the UV light-emitting diodes chips. Under irradiation of λ=350 nm, Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) have green and blue emissions, respectively. Luminescence of Ca2 Ga2 SiO7 :Tb(3+) , Li(+) phosphor varies with the different Tb(3+) contents. The thermal stability and energy-migration mechanism of Ca2 Ga2 SiO7 :Eu(2+) are also studied. The investigation results indicate that the prepared Ca2 Ga2 SiO7 :Eu(2+) and Ca2 Ga2 SiO7 :Ce(3+) , Li(+) samples show potential as green and blue phosphors, respectively, for UV-excited white-light-emitting diodes.

Enhancing photoluminescence performance of SrSi2O2N2:Eu(2+) phosphors by Re (Re = La, Gd, Y, Dy, Lu, Sc) substitution and its thermal quenching behavior investigation.

Eu(2+)-doped SrSi2O2N2 has recently been identified as a viable green phosphor that in conjunction with a blue-emitting diode can be used in solid-state white-lighting sources. In this study, we attempt to improve the photoluminescence and thermal quenching behavior by codoping Re(3+) (Re = La, Gd, Y, Dy, Lu, Sc) and Li(+) instead of Sr(2+). Trivalent cation substitution at the Sr(2+) site enhances the photoluminescence intensities and also achieves better thermal stability at high temperature. The lifetime decay properties in the related substituted phosphors are investigated. Furthermore, under the 460 nm blue light irradiation, this green phosphor exhibits excellent luminescence properties with absorption and internal/external efficiencies. High-color-rendition warm-white LEDs using the phosphor have the color temperature and color rendition of 4732 K and 91.2, respectively, validating its suitability for use in solid-state white lighting.

A novel efficient Mn4+ activated Ca14Al10Zn6O35 phosphor: application in red-emitting and white LEDs.

A new, highly efficient deep red-emitting phosphor Ca14Al10Zn6O35:Mn(4+) was developed as a component of solid-state white light-emitting diodes (LEDs). The structural and optical characterization of the phosphor is described. The phosphor exhibits strong emission in the range of 650-700 nm when excited by 460 nm excitation, with a quantum efficiency approaching 50%. Concentration dependence of Mn(4+) luminescence in Ca14Al10Zn6O35:Mn(4+) is investigated. Attempts to understand the thermal stability on the basis of the thermal quenching characteristics of Ca14Al10Zn6O35:Mn(4+) is presented. The results suggest that phosphors deriving from Ca14Al10Zn6O35:Mn(4+) have potential application for white LEDs. In addition, influence of cation substitution on the luminescence intensity of these phosphors is elucidated.

Ba(1.3)Ca(0.7)SiO4:Eu(2+),Mn(2+): a promising single-phase, color-tunable phosphor for near-ultraviolet white-light-emitting diodes.

In this paper, Eu(2+)-doped and Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors were synthesized by means of a conventional solid-state reaction process. The single-phase purity was checked by means of X-ray diffraction and the Rietveld method. Under excitation at 390 nm, the emission spectra of the Eu(2+)-doped phosphors exhibit a broad-band emission centered at 500 nm caused by the electric dipole allowed transition of the Eu(2+) ions. The emission spectra of codoped phosphors show one more broad emission centered at 600 nm attributable to the transitions from the (4)T1((4)G) → (6)A1((6)S) of Mn(2+) ions. The luminescent color of the codoped phosphors can be easily adjusted from blue to red with variation of the Mn(2+) content. The energy transfer mechanism from the Eu(2+) to Mn(2+) ions in Ba1.3Ca0.7SiO4 phosphors has been confirmed to be the resonant type via dipole-quadrupole interaction, and the critical distance has been calculated quantitatively. All these results demonstrate that the Eu(2+)/Mn(2+)-codoped Ba1.3Ca0.7SiO4 phosphors can be a promising single-phase, color-tunable phosphor for near-UV white-light-emitting diodes after a further optimization process. Additionally, a great red shift from 593 to 620 nm has been observed following the increase of Mn(2+) content, and the phenomenon has been discussed in relation to the changes in the crystal field surrounding the Mn(2+) ions and the exchange interactions caused by the formation of Mn(2+) pairs.

Tunable color of Ce3+/Tb3+/Mn(2+)-coactivated CaScAlSiO6 via energy transfer: a single-component red/white-emitting phosphor.

A series of single-component red/white-emitting CaScAlSiO6:Ce(3+),Tb(3+),Mn(2+) phosphors have been synthesized by a solid-state reaction. It is observed that CaScAlSiO6:Ce(3+),Tb(3+) phosphors exhibit two dominating bands situated at 380 and 542 nm, originating from the allowed 5d → 4f transition of the Ce(3+) ion and the (5)D4 → (7)F(J) = (J = 6, 5, 4, 3) transition of the Tb(3+) ion, respectively. As for CaScAlSiO6:Ce(3+),Mn(2+), our results indicate that Mn(2+) may occupy not only a Ca(2+) site to generate an orange emission [Mn(2+)(I)] at 590 nm but also a Sc(3+) site to generate a red emission [Mn(2+)(II)] at 670 nm. Both energy transfers from Ce(3+) to Tb(3+) and from Ce(3+) to Mn(2+) in the CaScAlSiO6 host are investigated and have been demonstrated to be of the resonant type via a dipole-dipole mechanism. By proper tuning of the relative composition of Tb(3+)/Mn(2+), white light can also be achieved upon excitation of UV light, indicating that the developed phosphor may potentially be used as a single-component red/white-emitting phosphor for UV-light-emitting diodes.

Tunable blue-green-emitting Ba3LaNa(PO4)3F:Eu2+,Tb3+ phosphor with energy transfer for near-UV white LEDs.

A series of Eu(2+) and Eu(2+)/Tb(3+) activated novel Ba3LaNa(PO4)3F phosphors have been synthesized by traditional solid state reaction. Rietveld structure refinement of the obtained phosphor indicates that the Ba3LaNa(PO4)3F host contains three kinds of Ba sites. The photoluminescence properties exhibit that the obtained phosphors can be efficiently excited in the range from 320 to 430 nm, which matches perfectly with the commercial n-UV LED chips. The critical distance of the Eu(2+) ions in Ba3LaNa(PO4)3F:Eu(2+) is calculated and the energy quenching mechanism is proven to be dipole-dipole interaction. Tunable blue-green emitting Ba3LaNa(PO4)3F:Eu(2+),Tb(3+) phosphor has been obtained by co-doping Eu(2+) and Tb(3+) ions into the host and varying their relative ratios. Compared with the Tb(3+) singly doped phosphor, the codoped phosphors have more intense absorption in the n-UV range and stronger emission of the Tb(3+) ions, which are attributed to the effective energy transfer from the Eu(2+) to Tb(3+) ions. The energy transfer from the Eu(2+) to Tb(3+) ions is demonstrated to be a dipole-quadrupole mechanism by the Inokuti-Hirayama (I-H) model. The Eu(2+) and Tb(3+) activated phosphor may be good candidates for blue-green components in n-UV white LEDs.

Regional horizontal ecological compensation and ecosystem service value based on water resources pattern and insurance gain.

Ecological compensation plays an important role in maintaining ecosystem services and promoting regional green development. We built a regional horizontal ecological compensation model based on water resources pattern and insurance gain, and which was used to solve the problems of single compensation method and low compensation efficiency. Taking the Beijing-Tianjin-Hebei region as an example, we analyzed water footprint and water ecological carrying capacity from 2000 to 2019. The compensation subject and object and water footprint compensation amount were determined according to the input cost of ecological protection and allocation factor. Then, the insurance pricing model was introduced to determine ecological insurance premium rate. We calculated insurance compensation, ecological compensation standard and different types of ecosystem service value. Results showed that the whole region was at a state of water ecological deficit, with the agricultural water footprint accounting for 94.5%. From the perspective of the compensation subject and object, Beijing and Tianjin, as the compensation subject, needed to pay 0.402 billion yuan and 0.396 billion yuan (the amount of compensation) to Hebei Province each year. Hebei Province obtained a total of 0.228 billion yuan of ecological insurance with an insurance premium rate of 1.4%, and should receive an average annual ecological compensation standard of 0.81 billion yuan from Beijing and Tianjin. Hydrological regulation was the core ecosystem service in the region, with an average value of 187.974 billion yuan. It was of strategic significance to introduce ecological insurance mechanism to construct horizontal ecological compensation mechanism, improve ecosystem service function, and enhance the value of ecosystem services in the study area.

Synthesis, structure, and luminescence properties of Europium/Cerium/Terbium doped strontium-anorthite-type green phosphor for solid state lighting.

Novel phosphor exploration and luminescence property regulation are two important strategies in pursing high performance phosphors for white light emitting diodes, and have attracted great attention from the researchers. Herein, novel green phosphors Sr2Ga2SiO7:Eu2+ and Sr2Ga2SiO7:Ce3+,Tb3+ had been obtained by high-temperature solid-state reactions and their luminescence properties had been investigated in detail. Powder X-ray diffraction and Rietveld structure refinement results verified the phase purity and gave the crystal structure of the prepared samples. Due to the electric dipole transition between inter configurations of 4fN and 4fN-15d1, Sr2Ga2SiO7:Eu2+ and Sr2Ga2SiO7:Ce3+ exhibited intense broad excitation and emission bands, giving out green and blue emitting light under UV excitation, respectively. By codoping Tb3+ with Ce3+ in the host and utilizing the energy transfer, tunable blue to green emission had been obtained. The energy transfer mechanism had been determined to be electric dipole-quadrupole interaction through dynamic luminescence analysis using I-H model. The prepared phosphors exhibited good thermal stability with integral emission intensity at 150 °C remaining more than 80 % of the emission intensity at 25 °C. Moreover, by coating Sr2Ga2SiO7:Eu2+ and Sr2Ga2SiO7:Ce3+,Tb3+ on UV chips, green LED devices had been obtained. The investigation results indicated that the Eu2+ singly doped and Ce3+-Tb3+ codoped Sr2Ga2SiO7 might be potential UV excited green phosphors for solid state lighting.

Pressure-induced distinct excitonic properties of 2D perovskites with isomeric organic molecules for spacer cations.

Spacer organic cations in two-dimensional (2D) perovskites play vital roles in inducing structural distortion of the inorganic components and dominating unique excitonic properties. However, there is still little understanding of spacer organic cations with identical chemical formulas, and different configurations have an impact on the excitonic dynamics. Herein, we investigate and compare the evolution of the structural and photoluminescence (PL) properties of [CH3(CH2)4NH3]2PbI4 ((PA)2PbI4) and [(CH3)2CH(CH2)2NH3]2PbI4 ((PNA)2PbI4) with isomeric organic molecules for spacer cations by combining steady-state absorption, PL, Raman and time-resolved PL spectra under high pressures. Intriguingly, the band gap is continuously tuned under pressure and decreased to 1.6 eV at 12.5 GPa for (PA)2PbI4 2D perovskites. Simultaneously, multiple phase transitions occur and the carrier lifetimes are prolonged. In contrast, the PL intensity of (PNA)2PbI4 2D perovskites exhibits an almost 15-fold enhancement at 1.3 GPa and an ultrabroad spectral range of up to 300 nm in the visible region at 7.48 GPa. These results indicate that the isomeric organic cations (PA+ and PNA+) with different configurations significantly mediate distinct excitonic behaviors due to different resilience to high pressures and reveal a novel interaction mechanism between organic spacer cations and inorganic layers under compression. Our findings not only shed light on the vital roles of isomeric organic molecules as organic spacer cations in 2D perovskites under pressure, but also open a route to rationally design highly efficient 2D perovskites incorporating such spacer organic molecules in optoelectronic devices.

Revealing photoluminescence mechanisms of single CsPbBr3/Cs4PbBr6 core/shell perovskite nanocrystals.

CsPbBr3 nanocrystals (NCs) encapsulated by Cs4PbBr6 has attracted extensive attention due to good stability and high photoluminescence (PL) emission efficiency. However, the origin of photoluminescence (PL) emission from CsPbBr3/Cs4PbBr6 composite materials has been controversial. In this work, we prepare CsPbBr3/Cs4PbBr6 core/shell nanoparticles and firstly study the mechanism of its photoluminescence (PL) at the single-particle level. Based on photoluminescence (PL) intensity trajectories and photon antibunching measurements, we have found that photoluminescence (PL) intensity trajectories of individual CsPbBr3/Cs4PbBr6 core/shell NCs vary from the uniform longer periods to multiple-step intensity behaviors with increasing excitation level. Meanwhile, second-order photon correlation functions exhibit single photon emission behaviors especially at lower excitation levels. However, the PL intensity trajectories of individual Cs4PbBr6 NCs demonstrate apparent "burst-like" behaviors with very high values of g 2(0) at any excitation power. Therefore, the distinguishable emission statistics help us to elucidate whether the photoluminescence (PL) emission of CsPbBr3/Cs4PbBr6 core/shell NCs stems from band-edge exciton recombination of CsPbBr3 NCs or intrinsic Br vacancy states of Cs4PbBr6 NCs. These findings provide key information about the origin of emission in CsPbBr3/Cs4PbBr6 core/shell nanoparticles, which improves their utilization in the further optoelectronic applications.