Blue-emitting Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+) phosphors for high CRI white LEDs

A broadband blue-emitting Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+)(x=0-0.2) phospho rs were synthesized,which can be used for near-UV pumped white light-emitting diodes(w-LEDs).The crystal structures,photoluminescence pro perties,external quantum efficiency,the rmal stability and application perfo rmance of Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+),by partially substituting Sr^(2+) with Ca^(2+)(x=0-0.2),were studied by various analytical techniques.When the Ca/Sr ratio of Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+) gradually increases,the emission peak of Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+) red-shiftes from 459 to 465 nm,corrected external quantum efficiency increases from 31.8% to 42.9%,and the thermal stability is also improved.The mechanism of the changes of the photoluminescence emission and excitation spectra,external quantum efficiency and thermal stability properties was also investigated in detail.In addition,a w-LED was fabricated by using SrLu_(2)O_(4):Ce^(3+)(blue),β-sialon:Eu^(2+)(green) and(Sr,Ca)AlSiN_(3):Eu^(2+)(red) phosphors combined with a 405 nm near-UV LED chip,and its color rendering index(CRI) reaches 96.0.When Sr_(0.8)Ca_(0.2)Lu_(2)O_(4):Ce^(3+) is applied as blue phosphor to substitute SrLu_(2)O_(4):Ce^(3+),the obtained w-LED devices have high luminous efficiency,and CRI greater than 95.0.These re sults show that the Sr_(1-x)Ca_(x)Lu_(2)O_(4):Ce^(3+) can be potential blue phosphors for n-UV pumped high CRI w-LEDs application.

Synthesis and luminescence properties of Mn^(3+),Bi^(3+) co-doped Y_6W0_(12) for blue phosphor

Mn^3＋ and Bi^3＋ co-doped Y6WO12 samples with hexagonal structure were synthesized via an improved salt pyrogenation method at a temperature region of 700-1100 ℃ for 3 h. In Y6WO12, Mn^3＋, substituting y^3＋, occupies a seven-coordination site and its energy levels are treated in near Oh symmetry. The samples doped by Mn^3＋ alone emit the most intensive blue light at 420 nm under excitation at 247 nm due to charge transition （CT）. The mechanism of sensitization of Bi^3＋ for Y6WO12：Mn^3＋ was also analyzed by taking account of metal-to-metal chargetransfer （MMCT） from Bi^3＋ to Mn^3＋. As a consequence, the phosphor Y6WO12：Mn^3＋/Bi^3＋ can emit blue light under radiation of 370 nm, and the emission intensity is enhanced about five times by the sensitizer Bi^3＋. The optimal doping concentration of Bi^3＋ is determined as 1 at% for the emission at 420 nm in Y6WO12：0.5 at% Mn^3＋ phosphors.

Formation of One-Dimensional van der Waals Heterostructures via Self-Assembly of Blue Phosphorene Nanoribbons to Carbon Nanotubes

Van der Waals heterostructures composed of low-dimensional atomic layers host rich physics for new device applications,such as magic-angle twisted bilayer graphene and coaxial multi-walled hetero-nanotubes.Aside from exploring their abnormal physical behavior,fabrication of such structures also presents a great challenge to this area,owing to the subtle and sensitive interactions among neighboring layers.Here we show by molecular dynamics simulations that narrow blue phosphorene nanoribbons can be encapsulated into carbon nanotubes driven by van der Waals interactions and form one-dimensional heterostructures.It shows that by varying carbon nanotube diameters and nanoribbon width,the nanoribbons can either retain their original straight structures or twist into tubular structures.Wrapping phases are also observed for large-sized blue phosphorus.It is found that the underlying mechanism originates from the competition between van der Waals energy and bending energy induced by tube curvature.A phase diagram of the resultant 1D structure is thus obtained based on a simple analysis of energetics.The results are expected to stimulate further experimental efforts in fabricating one-dimensional van der Waals heterostructues with desired functionality.