Efficient red luminescence in Eu3+ doped CdSe/CdS all-inorganic quantum dots shows great potential for wLEDs

Complete inorganic quantum dots (QDs) CdSe/CdS:Eu³⁺ with full transmittance were proposed as red color converters for white light emitting diodes (wLEDs) using a facile one-step melt quenching method. TEM, XPS, and XRD were used to verify the successful nucleation of CdSe/CdS:Eu³⁺ QDs in silicate glass. The results indicated that the incorporation of Eu contributed to the nucleation of CdSe/CdS QDs in silicate glass, where the nucleation time of the CdSe/CdS:Eu³⁺ QDs rapidly decreased in 1 h compared with other inorganic QDs that took more than 15 h. CdSe/CdS:Eu³⁺ inorganic QDs exhibited bright and long-term stable red luminescence under both UV and blue light excitation; up to 53.5% quantum yield and 8.05 ms fluorescence lifetime were obtained by adjusting the Eu³⁺ concentration. Based on the luminescence performance and absorption spectra, a possible luminescence mechanism was proposed. Moreover, the application potential of the CdSe/CdS:Eu³⁺ QDs in wLEDs was studied by coupling the CdSe/CdS:Eu³⁺ QDs and commercial Intematix G2762 green phosphor on a InGaN blue LED chip. Warm white light (5217 K) with 89.5 CRI and 91.1 lm W^-1 luminous efficacy could be achieved. Additionally, 91% of the NTSC color gamut was obtained, demonstrating the great potential of the CdSe/CdS:Eu³⁺ inorganic QDs as a color converter for wLEDs.

Defective Nature of CdSe Quantum Dots Embedded in Inorganic Matrices

Quantum dots (QDs) embedded in inorganic matrices have been extensively studied for their potential applications in lighting, displays, and solar cells. While a significant amount of research studies focused on their experimental fabrication, the origin of their relatively low photoluminescence quantum yield has not been investigated yet, although it severely hinders practical applications. In this study, we use time-dependent density functional theory (TDDFT) to pinpoint the nature of excited states of CdSe QDs embedded in various inorganic matrices. The formation of undercoordinated Se atoms and nonbridging oxygen atoms at the QD/glass interface is responsible for the localization of a hole wave function, leading to the formation of low-energy excited states with weak oscillator strength. These states provide pathways for nonradiative processes and compete with radiative emission. The photoluminescence performance is predicted for CdSe QDs in different matrices and validated by experiments. The results of this study have significant implications for understanding the underlying photophysics of CdSe QDs embedded in inorganic matrices that would facilitate the fabrication of highly luminescent glasses.

Ab Initio Molecular Dynamics of CdSe Quantum-Dot-Doped Glasses

We have probed the local atomic structure of the interface between a CdSe quantum dot (QD) and a sodium silicate glass matrix. Using ab initio molecular dynamics simulations, we determined the structural properties and bond lengths, in excellent agreement with previous experimental observations. On the basis of an analysis of radial distribution functions, coordination environment, and ring structures, we demonstrate that an important structural reconstruction occurs at the interface between the CdSe QD and the glass matrix. The incorporation of the CdSe QD disrupts the Na-O bonds, while stronger SiO₄ tetrahedra are reformed. The existence of the glass matrix breaks the stable 4-membered (4MR) and 6-membered (6MR) Cd-Se rings, and we observe a disassociated Cd atom migrated in the glass matrix. Besides, the formation of Se-Na and Cd-O linkages is observed at the CdSe QD/glass interface. These results significantly extend our understanding of the interfacial structure of CdSe QD-doped glasses and provide physical and chemical insight into the possible defect structure origin of CdSe QD, of interest to the fabrication of the highly luminescent CdSe QD-doped glasses.

Direct femtosecond laser-induced formation of CdS quantum dots inside silicate glass

We report the one-step precipitation of CdS quantum dots in the volume of CdS-doped silicate glass under the focused femtosecond laser beam without additional heat treatment of glass. Femtosecond direct laser writing leads to the annular distribution of the precipitated CdS quantum dots in laser-written domain optical properties of which could be tuned by laser beam parameters. Increasing the laser pulse number to 10³ significantly enhances luminescence intensity in the domains, while further increasing up to 10⁶ pulses leads to luminescence quenching. A possible scenario for the formation and distribution of quantum dots is proposed.