Temperature-Dependent Exciton and Trap-Related Photoluminescence of CdTe Quantum Dots Embedded in a NaCl Matrix: Implication in Thermometry.

Temperature-dependent optical studies of semiconductor quantum dots (QDs) are fundamentally important for a variety of sensing and imaging applications. The steady-state and time-resolved photoluminescence properties of CdTe QDs in the size range from 2.3 to 3.1 nm embedded into a protective matrix of NaCl are studied as a function of temperature from 80 to 360 K. The temperature coefficient is found to be strongly dependent on QD size, with the highest sensitivity obtained for the smallest size of QDs. The emission from solid-state CdTe QD-based powders is maintained with high color purity over a wide range of temperatures. Photoluminescence lifetime data suggest that temperature dependence of the intrinsic radiative lifetime in CdTe QDs is rather weak, and it is mostly the temperature-dependent nonradiative decay of CdTe QDs which is responsible for the thermal quenching of photoluminescence intensity. By virtue of the temperature-dependent photoluminescence behavior, high color purity, photostability, and high photoluminescence quantum yield (26%-37% in the solid state), CdTe QDs embedded in NaCl matrices are useful solid-state probes for thermal imaging and sensing over a wide range of temperatures within a number of detection schemes and outstanding sensitivity, such as luminescence thermochromic imaging, ratiometric luminescence, and luminescence lifetime thermal sensing.

Kalytchuk S ，Zhovtiuk O ，Kershaw SV ，Zbořil R ，Rogach AL ... -  《-》

Exciton-phonon scattering and nonradiative relaxation of excited carriers in hydrothermally synthesized CdTe quantum dots.

Jagtap AM ，Khatei J ，Koteswara Rao KS 《-》

Large exciton binding energy, high photoluminescence quantum yield and improved photostability of organo-metal halide hybrid perovskite quantum dots grown on a mesoporous titanium dioxide template.

Herein, we demonstrated a novel synthetic route to grow size-tunable hybrid perovskite (CH3NH3PbI3 and CH3NH3PbBr3) quantum dots (QDs) using a Fluorine-doped TiO2 (F-TiO2) mesoporous template and these QDs exhibit large exciton binding energy, high photoluminescence quantum yield and improved photostability. The pore size in F-TiO2 template is tuned by varying the HF molar concentration during its solvothermal growth and size of the perovskite QDs embedded in F-TiO2 pores is tuned in the range 1.7-5.1 nm, as revealed from the TEM analysis. A systematic blue-shift in UV-visible absorption edge, as well as photoluminescence (PL) spectrum, is observed with the reduced size of the perovskite QDs due to strong quantum confinement. The CH3NH3PbI3 QD with average size ∼1.7 nm exhibits ∼47 nm blue shift in the PL spectra, ∼43 fold enhancement in PL intensity and ∼25% PL quantum yield (QY). On the other hand, CH3NH3PbBr3 QD of similar size exhibits dramatically enhanced (∼124 times) PL emission with narrow line width and a PLQY of ∼57%, which is significant for the template-assisted growth of perovskite QDs film. The quantitative analysis of the PL emission energy vs QD size shows an excellent fit with the Brus equation confirming the strong quantum confinement effect in the perovskite QDs. Analysis of low-temperature PL spectra reveals very high exciton binding energy (162-272 meV) for the QDs as compared to the bulk film (32 meV) due to the high effective dielectric constant, and high electron-hole recombination probability in the QDs, which is consistent with the extremely high PLQY and stable emission from the QDs. The blue shift of the PL peak with increasing temperature is explained on the basis of localization effect. Time-resolved PL analysis for both the perovskite QDs reveals faster life time compared to their bulk counterparts, confirming the significant radiative recombination of carriers in the QDs at the room temperature. The CH3NH3PbBr3 QDs embedded in porous F-TiO2 template maintain its initial PL intensity up to several hours (≥10 h) under the UV laser exposure (18mW), while that of the bulk film decreases to <67%. Thus, template grown hybrid perovskite QDs exhibiting high photostability and very high PLQY demonstrated here are promising for the next generation optoelectronic applications.

Parveen S ，Paul KK ，Das R ，Giri PK ... -  《-》

Volatile interface of biological oxidant and luminescent CdTe quantum dots: implications in nanodiagnostics.

Priyam A ，Bhattacharya SC ，Saha A 《-》

Carbon Dot Nanothermometry: Intracellular Photoluminescence Lifetime Thermal Sensing.

Kalytchuk S ，Poláková K ，Wang Y ，Froning JP ，Cepe K ，Rogach AL ，Zbořil R ... -  《-》