Luminescence enhancement of BaMgSiO_4:Eu^(2+) by adding borate as flux

The luminescence of EU^2＋ in BaMgSiO4 with BaB2O4 as flux was studied. The emission spectrum of the phosphor consisted of two bands, peaking at about 398 nm and 515 nm, which were attributed to the emissions from different Eu^2＋ sites in the lattice. When the BaB2O4 flux was applied, the intensity of the 398 nm emission was not clearly affected, but the intensity of the 515 nm emission was enhanced by about ten times. Gaussian fitting showed that the emission band at around 515 nm could actually be resolved into two bands with peak wavelengths of 499 nm and 521 nm, respectively. The assignments of the emission bands to the cation sites were carried out according to the values of bond valence. The overlapping of the 398 nm emission band on the excitation band of 515 nm emission implied that energy transfer could occur from the luminescent center related to the 398 nm emission to the center related to the 515 nm emission, and the energy transfer process remarkably enhanced the intensity of the 515 nm emission band. The phosphor had strong excitation at around 350-400 nm and emitted a bright green luminescence. Thus it could have applications as a green component in solid-state lighting devices assembled by near-UV Light Emitting Diodes （LED） combined with tricolor phosphors.

Fabrication of High-power White LEDs and White Light Uniformity Testing

As the blue and yellow lights are complementary colors, a blue InGaN LED chip is coated hy a yellow phosphor film to generate white light based on luminescence conversion mechanism. The emitted light of a blue LED is used as the primary source for exciting fluorescent material such as cerium doped yttrium aluminum garnet with the formula Y3Al2O12 ： Ce^3＋ （in short： YAG ： Ce^3＋ ）. The matching of the spectrum of the blue LED chips and the YAG ： Ce^3＋ yellow phosphor is studied to improve the conversion efficiency. The packaging methods and manufacturing processes for high power single chip-white LEDs are introduced. The uniformity of the output white light is investigated. Based on the characteristics of the high power white LEDs, some approaches and processes are suggested to improve the light uniformity when they are fabricated. The effectiveness of those approaches on the improvement of LEDs is discussed in detail and some interesting conclusions are also presented.

Directional emissions from perovskite nanocrystals thin film enabled by metasurface integration through one step spin-coating process

Advances in thin film light-emitting devices have fueled the rapid growth of a new class of solid-state lighting devices,featuring low fabrication cost,high quantum efficiency,broadband spectrum coverage,etc.In contrast to the conventional inorganic semiconductors that rely on lattice matched high crystalline quality substrate,solution processable thin films eliminate the dependence on the substrate,which is highly desired for the ease and versatility of integrations with foreign medium.By taking this advantage,this work developed an ultracompact solution to control the directionality of thin film emitters using integrated dielectric metasurface through one step spin-coating process.As a proof of concept,directional emissions from perovskite nanocrystal thin film,including collimated light emissions and two-dimensional beam steering,are experimentally demonstrated.Notably,our approach,where light emitters were integrated on the back side of substrate after the fabrication of metasurface,judiciously avoids any potential degradation of material optical quality caused by the multi-step nanofabrication.Therefore,it can serve as a generalized scheme to engage the advantageous properties of dielectric metasurface,including the compactness,high efficiency,beam controllability with the emerging thin film light-emitting diodes(LEDs),which is applicable to a wide range of solution processable materials,including organic light-emitting diodes,quantum-dot light emitting diodes,polymer LEDs,and perovskite LEDs,opening up new pathways to develop low-cost and ultra-compact solid state light sources with versatile beams characteristics.

Advances in luminescent lanthanide complexes and applications

Luminescent lanthanide complexes have been widely investigated as light emitting materials in bio-imaging and sensing, solid state lighting and display, anti-fake tags and light conversion films, due to their characterized photophysical properties including large Stokes shift, long lifetime, and sharp emission spectrum, arising from the sensitized f-f transitions. In this review, we summarize the most recent advances in luminescent lanthanide complexes and their applications from 2015 to August 2017 concerning of general concepts to potential applications. We first introduce the basic concept of sensitized luminescence of lanthanide complexes and the strategies used for highly luminescent complexes. Then recent varieties of luminescent lanthanide complexes and their hybrid materials are presented. Finally, applications are discussed in detail.

Combustion synthesis of Ce^(3+), Eu^(3+) and Dy^(3+) activated NaCaPO_4 phosphors

The preparation of NaCaPO4 doped with rare earth （RE） ions Ce3＋, Eu3＋ and Dy3＋ by combustion method was described. Under UV excitation （251 nm） of NaCaPO4：Ce3＋ showsd emission （367 nm） in UV range. When NaCaPO4：Dy3＋ phosphor was excited at 349 nm, the emission spectrum showed intense bands at 482 nm （blue） and 576 nm （yellow）. In Eu activated NaCaPO4 phosphor, the emission spectrum showed a dominant peak at 594 nm （orange） while others were at 614 and 621 nm （red） when excited at 393 nm. The prepared phosphor was characterized by X-ray diffraction （XRD）, scanning electron microscope （SEM） and photoluminescence （PL） measurement. Thus, the photoluminescence behavior of NaCaPO4：Ce3＋ was strongly suggested for scintillator. Likewise, Eu3＋ and Dy3＋ activated NaCaPO4 phosphors were recommended for near-UV white light-emitting diodes （LEDs）.

Multifunctional Dy(Ⅲ)doped di-calcium silicate array for boosting display and forensic applications

Latent fingerprints（LFPs） are the major physical evidences for the identification of individuals during crime spot investigation. Till date, numerous methods were followed to visualize LFPs. However, simple,accurate, and cost-effective method has wide scope in advanced forensic field. In our work, Ca2 SiO4：Dy^（3＋）nanopowders（NPs） were fabricated via solution combustion route. The optimized sample was employed for the visualization of overlapped LFPs by the cost effective powder dusting method. The obtained results reveals the complete three levels of ridge characteristics with high sensitivity, reproducibility,selectivity, and reliability on various complex surfaces. The photoluminescence（PL） spectra consist of intense peaks at ～ 480 and 574 nm owing to ~4 F（9/2） →~6 H（15/2） and ~4 F（9/2）→~6 H（13/2） 4 f transitions of Dy3＋ ions,respectively. The photometric properties confirm that the samples exhibit intense white emission with high color purity. Therefore, the prepared NPs could be a definitive choice as an advanced luminescent NPs for forensic, solid state lighting and portable FED devices.