Efficient Diffusive Transport of Hot and Cold Excitons in Colloidal Type II CdSe/CdTe Core/Crown Nanoplatelet Heterostructures

Cadmium chalcogenide colloidal quantum wells or nanoplatelets (NPLs), a class of new materials with atomically precise thickness and quantum confinement energy, have shown great potential in optoelectronic applications. Short exciton lifetimes in two-dimensional (2D) NPLs can be improved by the formation of type II heterostructures, whose properties depend critically on the mechanism of exciton transport. Herein, we report a study of room-temperature exciton in-plane transport mechanisms in type-II CdSe/CdTe core/crown (CC) colloidal NPL heterostructures with the same CdSe core and different CdTe crown sizes. Photoluminescence excitation measurements show unity quantum efficiency for transporting excitons created at the crown to the CdSe/CdTe interface (to form lower-energy charge-transfer excitons). At near band edge excitation, the crown-to-core transport time increases with crown size (from 2.7 to 5.6 ps), and this size-dependent transport can be modeled well by 2D diffusion of thermalized excitons in the crown with a diffusion constant of 2.5 ± 0.3 cm²/s (about a factor of 1.6 times smaller than the bulk value). With excitation energy above the band edge, there is an increased contribution of hot exciton transport (up to 7% of the total excitons at 400 nm excitation with diffusion constant that is over twice that of cold excitons). The percentage of hot exciton transport decreases with increasing NPL sizes and decreasing excess excitation photon energy. The observed ultrafast and efficient hot and cold exciton crown-to-core transport suggests their potential applications as light-harvesting and light-emitting materials

Low Threshold Multiexciton Optical Gain in Colloidal CdSe/CdTe Core/Crown Type-II Nanoplatelet Heterostructures

Colloidal cadmium chalcogenide core/crown type-II nanoplatelet heterostructures, such as CdSe/CdTe, are promising materials for lasing and light-emitting applications. Their rational design and improvement requires the understanding of the nature of single- and multiexciton states. Using pump fluence and wavelength-dependent ultrafast transient absorption spectroscopy, we have identified three spatially and energetically distinct excitons (in the order of increasing energy): interface-localized charge transfer exciton (X_CT, with electron in the CdSe core bound to the hole in the CdTe crown), and CdTe crown-localized X_CdTe and CdSe core-localized X_CdSe excitons. These exciton levels can be filled sequentially, with each accommodating two excitons (due to electron spin degeneracy) to generate one to six exciton states (with lifetimes of ≫1000, 209, 43.5, 11.8, 5.8, and 4.5 ps, respectively). The spatial separation of these excitons prolongs the lifetime of multiexciton states. Optical gain was observed in tri- (XX_CTX_CdTe) and four (XX_CTXX_CdTe) exciton states. Because of the large absorption cross section of nanoplatelets, an optical gain threshold as low as ∼43 μJ/cm² can be achieved at 550 nm excitation for a colloidal solution sample. This low gain threshold and the long triexciton (gain) lifetime suggest potential applications of these 2D type-II heterostructures as low threshold lasing materials

Efficient and Ultrafast Formation of Long-Lived Charge-Transfer Exciton State in Atomically Thin Cadmium Selenide/Cadmium Telluride Type-II Heteronanosheets

Colloidal cadmium chalcogenide nanosheets with atomically precise thickness of a few atomic layers and size of 10–100 nm are two-dimensional (2D) quantum well materials with strong and precise quantum confinement in the thickness direction. Despite their many advantageous properties, excitons in these and other 2D metal chalcogenide materials are short-lived due to large radiative and nonradiative recombination rates, hindering their applications as light harvesting and charge separation/transport materials for solar energy conversion. We showed that these problems could be overcome in type-II CdSe/CdTe core/crown heteronanosheets (with CdTe crown laterally extending on the CdSe nanosheet core). Photoluminesence excitation measurement revealed that nearly all excitons generated in the CdSe and CdTe domains localized to the CdSe/CdTe interface to form long-lived charge transfer excitons (with electrons in the CdSe domain and hole in the CdTe domain). By ultrafast transient absorption spectroscopy, we showed that the efficient exciton localization efficiency could be attributed to ultrafast exciton localization (0.64 ± 0.07 ps), which was facilitated by large in-plane exciton mobility in these 2D materials and competed effectively with exiton trapping at the CdSe or CdTe domains. The spatial separation of electrons and holes across the CdSe/CdTe heterojunction effectively suppressed radiative and nonradiative recombination processes, leading to a long-lived charge transfer exciton state with a half-life of ∼41.7 ± 2.5 ns, ∼30 times longer than core-only CdSe nanosheets

High-Efficiency Optical Gain in Type-II Semiconductor Nanocrystals of Alloyed Colloidal Quantum Wells

Colloidal nanocrystals having controlled size, tailored shape, and tuned composition have been explored for optical gain and lasing. Among these, nanocrystals having Type-II electronic structure have been introduced toward low-threshold gain. However, to date, their performance has remained severely limited due to diminishing oscillator strength and modest absorption cross-section. Overcoming these problems, here we realize highly efficient optical gain in Type-II nanocrystals by using alloyed colloidal quantum wells. With composition-tuned core/alloyed-crown CdSe/CdSe_<i>x</i>Te_1–<i>x</i> quantum wells, we achieved amplified spontaneous emission thresholds as low as 26 μJ/cm², long optical gain lifetimes (τ_gain ≈ 400 ps), and high modal gain coefficients (<i>g</i>_modal ≈ 930 cm^–1). We uncover that the optical gain in these Type-II quantum wells arises from the excitations localized to the alloyed-crown region that are electronically coupled to the charge-transfer state. These alloyed heteronanostructures exhibiting remarkable optical gain performance are expected to be highly appealing for future display and lighting technologies

Table_2_Crosstalk of necroptosis and pyroptosis defines tumor microenvironment characterization and predicts prognosis in clear cell renal carcinoma.docx

Pyroptosis and necroptosis are two recently identified forms of immunogenic cell death in the tumor microenvironment (TME), indicating a crucial involvement in tumor metastasis. However, the characteristics of necroptosis and pyroptosis that define tumor microenvironment and prognosis in ccRCC patients remain unknown. We systematically investigated the transcriptional variation and expression patterns of Necroptosis and Pyroptosis related genes (NPRGs). After screening the necroptosis-pyroptosis clusters, the potential functional annotation for clusters was explored by GSVA enrichment analysis. The Necroptosis-Pyroptosis Genes (NPG) scores were used for the prognosis model construction and validation. Then, the correlations of NPG score with clinical features, cancer stem cell (CSC) index, tumor mutation burden (TMB), TME, and Immune Checkpoint Genes (ICGs) were also individually explored to evaluate the prognosis predictive values in ccRCC. Microarray screenings identified 27 upregulated and 1 downregulated NPRGs. Ten overall survival associated NPRGs were filtered to construct the NPG prognostic model indicating a better prognostic signature for ccRCC patients with lower NPG scores (P< 0.001), which was verified using the external cohort. Univariate and multivariate analyses along with Kaplan-Meier survival analysis demonstrated that NPG score prognostic model could be applied as an independent prognostic factor, and AUC values of nomogram from 1- to 5- year overall survival with good agreement in calibration plots suggested that the proposed prognostic signature possessed good predictive capabilities in ccRCC. A high-/sNPG score is proven to be connected with tumor growth and immune-related biological processes, according to enriched GO, KEGG, and GSEA analyses. Comparing patients with a high-NPG score to those with a low-NPG score revealed significant differences in clinical characteristics, growth and recurrence of malignancies (CSC index), TME cell infiltration, and immunotherapeutic response (P< 0.005), potentially making the NPG score multifunctional in the clinical therapeutic setting. Furthermore, AIM2, CASP4, GSDMB, NOD2, and RBCK1 were also found to be highly expressed in ccRCC cell lines and tumor tissues, and GASP4 and GSDMB promote ccRCC cells’ proliferation, migration, and invasion. This study firstly suggests that targeting the NPG score feature for TME characterization may lend novel insights into its clinical applications in the prognostic prediction of ccRCC.</p

Image_1_Crosstalk of necroptosis and pyroptosis defines tumor microenvironment characterization and predicts prognosis in clear cell renal carcinoma.tiff

Pyroptosis and necroptosis are two recently identified forms of immunogenic cell death in the tumor microenvironment (TME), indicating a crucial involvement in tumor metastasis. However, the characteristics of necroptosis and pyroptosis that define tumor microenvironment and prognosis in ccRCC patients remain unknown. We systematically investigated the transcriptional variation and expression patterns of Necroptosis and Pyroptosis related genes (NPRGs). After screening the necroptosis-pyroptosis clusters, the potential functional annotation for clusters was explored by GSVA enrichment analysis. The Necroptosis-Pyroptosis Genes (NPG) scores were used for the prognosis model construction and validation. Then, the correlations of NPG score with clinical features, cancer stem cell (CSC) index, tumor mutation burden (TMB), TME, and Immune Checkpoint Genes (ICGs) were also individually explored to evaluate the prognosis predictive values in ccRCC. Microarray screenings identified 27 upregulated and 1 downregulated NPRGs. Ten overall survival associated NPRGs were filtered to construct the NPG prognostic model indicating a better prognostic signature for ccRCC patients with lower NPG scores (P< 0.001), which was verified using the external cohort. Univariate and multivariate analyses along with Kaplan-Meier survival analysis demonstrated that NPG score prognostic model could be applied as an independent prognostic factor, and AUC values of nomogram from 1- to 5- year overall survival with good agreement in calibration plots suggested that the proposed prognostic signature possessed good predictive capabilities in ccRCC. A high-/sNPG score is proven to be connected with tumor growth and immune-related biological processes, according to enriched GO, KEGG, and GSEA analyses. Comparing patients with a high-NPG score to those with a low-NPG score revealed significant differences in clinical characteristics, growth and recurrence of malignancies (CSC index), TME cell infiltration, and immunotherapeutic response (P< 0.005), potentially making the NPG score multifunctional in the clinical therapeutic setting. Furthermore, AIM2, CASP4, GSDMB, NOD2, and RBCK1 were also found to be highly expressed in ccRCC cell lines and tumor tissues, and GASP4 and GSDMB promote ccRCC cells’ proliferation, migration, and invasion. This study firstly suggests that targeting the NPG score feature for TME characterization may lend novel insights into its clinical applications in the prognostic prediction of ccRCC.</p