Stable and efficient phosphor systems for white light-emitting diodes (LEDs) are highly important with respect to their application in solid-state lighting beyond the technical limitations of traditional lighting technologies. Therefore, inorganic solid-state conversion phosphors must be precisely selected and evaluated with regard to their special material properties and synergistic optical parameters. In this perspective, we present an overview of the recent developments of LED phosphors; firstly, general photoluminescence-controlling strategies for phosphors to match LED applications have been evaluated; secondly, state-of-the-art and emerging new LED phosphors have been demonstrated. Then, methodologies for the discovery of new LED phosphors by mineral-inspired prototype evolution and new phase construction, as well as combinatorial optimization screening, and the single-particle-diagnosis approach, have been analyzed and exemplified. Finally, future developments of LED phosphors have been proposed.

Semiconductive transition metal dichalcogenides (TMDs) have been considered as next generation semiconductors, but to date most device investigations are still based on microscale exfoliation with a low yield. Wafer scale growth of TMDs has been reported but effective doping approaches remain challenging due to their atomic thick nature. In this work, we report the synthesis of wafer-scale continuous few-layer PtSe 2 films with effective doping in a controllable manner. Chemical component analyses confirm that both n-and pdoping can be effectively modulated through the controlled selenization process. We systematically study the electrical properties of PtSe 2 films by fabricating top-gated field effect transistors (FETs). The device current on/off ratio is optimized in two-layer PtSe 2 FETs, and four-terminal configuration displays a reasonably high effective field effect mobility (14 and 15 cm 2 V -1 s -1 for p-and n-type FETs, respectively) with a nearly symmetric p-and n-type performance. Temperature dependent measurement reveals that the variable range hopping is dominant at low temperature. To further establish the feasible application based on controllable doping of PtSe 2 , a logic inverter and vertically stacked p-n junction arrays are demonstrated. These results validate that PtSe 2 is a promising candidate among the family of TMDs for future functional electronic applications.

2D layered materials (2DLMs) have gained tremendous interest for their potential applications in next-generation electronic, optoelectronic, [1][2][3] and energy devices. Although graphene possesses the highest reported mobility, its gapless nature motivates the pursuit of semiconductive transition metal dichalcogenides (TMDs) such as MoS 2 , [4][5][6] which has been intensively investigated based on mechanically exfoliated sheets. Yet for practical Atomic thin transition-metal dichalcogenides (TMDs) are considered as an emerging platform to build next-generation semiconductor devices. However, to date most devices are still based on exfoliated TMD sheets on a micrometer scale. Here, a novel chemical vapor deposition synthesis strategy by introducing multilayer (ML) MoS 2 islands to improve device performance is proposed. A four-probe method is applied to confirm that the contact resistance decreases by one order of magnitude, which can be attributed to a conformal contact by the extra amount of exposed edges from the ML-MoS 2 islands. Based on such continuous MoS 2 films synthesized on a 2 in. insulating substrate, a top-gated field effect transistor (FET) array is fabricated to explore key metrics such as threshold voltage (V T ) and field effect mobility (μ FE ) for hundreds of MoS 2 FETs. The statistical results exhibit a surprisingly low variability of these parameters. An average effective μ FE of 70 cm 2 V −1 s −1 and subthreshold swing of about 150 mV dec −1 are extracted from these MoS 2 FETs, which are comparable to the best top-gated MoS 2 FETs achieved by mechanical exfoliation. The result is a key step toward scaling 2D-TMDs into functional systems and paves the way for the future development of 2D-TMDs integrated circuits. Field Effect TransistorsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201803465. application, wafer-scale synthesis of highquality, continuous MoS 2 film is highly desired. Recently, the chemical vapor deposition (CVD) technique has been applied to produce single-layer (1L) MoS 2 films with moderate electrical performance [7][8][9][10] and so far the largest number of logic gates is 115. [11][12][13] Mechanically exfoliated multilayer (ML) MoS 2 have shown improved mobility and drive currents because of thicker channel with higher density of states. [14,15] A smaller bandgap associated with ML-MoS 2 [16,17] is also more appropriate for device performance engineering. [18][19][20] However, it is rather difficult to grow a uniform and continuous multilayer MoS 2 film since precise control of layer number of stacked MoS 2 remains unsolved, [21,22] and vertical growth is limited by the interlayer diffusion rate of S atoms (much slower than in-plane diffusion) and high surface energy. [23] Besides, it is rather difficult to maintain a planar growth in a controllable manner, instead most results simultaneously produce a mixture of monolayer, multilayer, and empty islands. [24,25] Despite the demand of high-quality wa...

Two-dimensional (2D) layered transition metal dichalcogenides (TMDs) have attracted significant interest in various optoelectronic applications due to their excellent nonlinear optical properties. One of the most important applications of TMDs is to be employed as an extraordinary optical modulation material (e.g., the saturable absorber (SA)) in ultrafast photonics. The main challenge arises while embedding TMDs into fiber laser systems to generate ultrafast pulse trains and thus constraints their practical applications. Herein, few-layered WS with a large-area was directly transferred on the facet of the pigtail and acted as a SA for erbium-doped fiber laser (EDFL) systems. In our study, WS SA exhibited remarkable nonlinear optical properties (e.g., modulation depth of 15.1% and saturable intensity of 157.6 MW cm) and was used for ultrafast pulse generation. The soliton pulses with remarkable performances (e.g., ultrashort pulse duration of 1.49 ps, high stability of 71.8 dB, and large pulse average output power of 62.5 mW) could be obtained in a telecommunication band. To the best of our knowledge, the average output power of the mode-locked pulse trains is the highest by employing TMD materials in fiber laser systems. These results indicate that atomically large-area WS could be used as excellent optical modulation materials in ultrafast photonics.

Chemical vapor deposition synthesis of semiconducting transition metal dichalcogenides (TMDs) offers a new route to build next-generation semiconductor devices. But realization of continuous and uniform multilayer (ML) TMD films is still limited by their specific growth kinetics, such as the competition between surface and interfacial energy. In this work, a layer-bylayer vacuum stacking transfer method is applied to obtain uniform and non-destructive ML-MoS 2 films. Back-gated field effect transistor (FET) arrays of 1L-and 2L-MoS 2 are fabricated on the same wafer, and their electrical performances are compared. We observe a significant increase of field-effect mobility for 2L-MoS 2 FETs, up to 32.5 cm 2 V −1 s −1 , which is seven times higher than that of 1L-MoS 2 (4.5 cm 2 V −1 s −1 ). Then we also fabricated 1L-, 2L-, 3L-, and 4L-MoS 2 FETs to further investigate the thickness-dependent characteristics of transferred ML-MoS 2 . Measurement results show a higher mobility but a smaller current on/off ratio as the layer number increases, suggesting that a balance between mobility and current on/ off ratio can be achieved in 2L-and 3L-MoS 2 FETs. Dual-gated structure is also investigated to demonstrate an improved electrostatic control of the ML-MoS 2 channel.