Ultrasmall pure hexagonal phase NaYF 4 :Yb,Er is successfully prepared via the solvothermal method. The upconversion (UC) luminescence of hexagonal phase NaYF 4 :Yb,Er nanocrystals is ten times stronger than that of cubic phase nanocrystals with the same size of 6 nm. XRD results reveal that heating above 673 K leads to conversion of the hexagonal phase to the high-temperature cubic phase, whereas the cubic nanocrystals undergo phase transformation from normal cubic at room temperature to hexagonal at 673 K and further to high-temperature cubic above 773 K. The hexagonal nanocrystals exhibit emission enhancement after heat treatment up to 573 K. Further heating above 773 K induces a decreasing trend in emission due to the phase transition to the high-temperature cubic phase. The cubic phase exhibits decreasing luminescence with temperature due to strong cross relaxation and then increasing luminescence above the temperature of 673 K due to the hexagonal phase transformation. The luminescent properties of both the normal cubic phase and high-temperature cubic phase indicate that different crystal fields exist in these two phases due to the rearrangement of ligands around Er 3+ at high temperature.
In this work, Mn2+-doped ZnS nanorods were synthesized
by a facile hydrothermal method. The morphology, structure, and composition
of the as-prepared samples were investigated. The temperature-dependent
photoluminescence of ZnS:Mn nanorods was analyzed, and the corresponding
activation energies were calculated by using a simple two-step rate
equation. Mn2+-related orange emission (4T1 → 6A1) demonstrates high stability
and is comparatively less affected by the temperature variations than
the defect-related emission. A metal–semiconductor–metal
junction ultraviolet photodetector based on the nanorod networks has
been fabricated by a cost-effective method. The device exhibits visible
blindness, superior ultraviolet photodetection with a responsivity
of 1.62 A/W, and significantly fast photodetection response with the
rise and decay times of 12 and 25 ms, respectively.
In this paper, ZnO nanoparticles doped with varying amount of Co content (i.e., 0, 2, 4, 6, 8, and 10 at.%) have been prepared by wet chemical route. X-ray diffraction (XRD) results reveal the successful substitution of Co 2+ ions on to sites of Zn 2+ ions without forming any secondary phase. Furthermore, a linear increase in d-spacing of the ZnO lattice is found with the increase in Co content. SEM images demonstrate the formation of homogeneously distributed spherical nanoparticles with average size of 50–70 nm. It is observed from optical investigations that band gap energy of ZnO nanoparticles significantly decreased with the increase in Co doping level. Interestingly, it is found that the high Co dopant concentration can lead to room temperature ferromagnetism in ZnO nanoparticles.
Establishment of essential conditions of different phases of NaYF4 and their utilization for the synthesis of core/shell structures to achieve the enhancement of UCL intensities.
Aluminum quantum dots (AlQDs) are an emerging class of optical material due to their unique photoluminescence in the ultraviolet waveband. Herein, a strategy is presented to control their photoluminescence emission. The synthesized AlQDs displayed photoluminescence from the UV-B region (<320 nm) to the near-ultraviolet region (∼425 nm) and high quantum yields. Our investigation revealed that surfactants and phosphonic acids (PAs) were competitively bound to the surface of AlQDs, and this was affected by the space volume of surfactants and charge of head groups. The steady-state and time-resolved spectroscopic data suggested the emission properties of AlQDs mainly originated from the surface-mediated states. The red-shifting of emission peak was a result of increased amount of PAs on the surface of AlQDs, which could be related to the surface oxygen presented in both ligands and surfactants. Overall, this study indicates a method to control the photoluminescence of AlQDs by changing the surfactants and surface ligands, which is fundamental to their applications in photonics and applications to energy and environment, in addition to biomedicine.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.