Garnet-Type Nanophosphors for White LED Lighting

Abstract

In this article we present a short review of the main wet chemical methods developed for the preparation of Ce 3+ -doped Y 3 Al 5 O 12 (YAG:Ce) nanocrystals for their use as nanophosphors in LED lighting technology: combustion, co-precipitation, sol-gel, modified-Péchini, and solvothermal routes. We highlight the key synthesis steps and discuss them in the view of the size, crystal quality, and agglomeration state of the obtained nanocrystals. The photoluminescence internal quantum yield of these nanocrystals is also discussed in light of their morphology. In addition, we report on other garnet-type nanophosphors [Gd 3 Sc 2 Al 3 O 12 , (Gd,Y) 3 Al 5 O 12 , etc.] doped with lanthanide ions (Ce 3+ , but also Eu 3+ or Dy 3+ ) developed with the goal of obtaining a warmer white light. The spectroscopic properties of these nanophosphors, in particular their emission range, is discussed in relation with the doping nature, doping concentration, and crystal field of the host matrices.

Ultra‐Small YPO4‐YAG:Ce Composite Nanophosphors with a Photoluminescence Quantum Yield Exceeding 50%

“…Indeed, the PXRD refinement as well as the EPR reveal that the dispersion of P and extra Y as foreign atoms has induced a structure distortion on the YAG host. According to the conclusion drawn by Ueda et al and others, [ 38,1 ] we believe that the change of the local Ce 3+ environment was caused by a change of electronic structure around Ce centers via the distortion of the host by the addition of a small amount of P and extra Y, which is responsible for the altered the PL properties. This electronic structure change can be evidenced by the increasing shift of Ce 3d peaks toward the higher binding energy, which begins with a small quantity of extra Y and P addition in the XPS spectra (Figure 6a), possibly caused by a change of electronegativity of nearby atoms of Ce when a substitution of atoms occurs.…”

“…The material is perfectly suited for these kind of applications, as it has a strong absorption in the blue spectral region, high quantum yield, and good chemical and physical stability at elevated temperatures. [1,2] However, for the ultra-small colloidal YAG:Ce nanoparticles ("NPs", i.e., with a particle dia meter < 50 nm in suspension), meeting the required ultra-small particle size and high photoluminescence (PL) performance (i.e., high photoluminescence quantum yield, "PLQY" or "QY" in short) simultaneously is challenging, as a particle size/ crystallinity trade-off has been observed previously. [2][3][4] In this paper, we refer to particle size as the "hydrodynamic particle size", i.e., the size measured with Synthesis of high quality colloidal Cerium(III) doped yttrium aluminum garnet (Y 3 Al 5 O 12 :Ce 3+ , "YAG:Ce") nanoparticles (NPs) meeting simultaneously both ultra-small size and high photoluminescence (PL) performance is challenging, as generally a particle size/PL trade-off has been observed for this type of nanomaterials.…”

Effect of surface treatment upon luminous efficiency of YAG: Ce ceramics

“…White light‐emitting diodes (WLEDs) have been widely used as an emerging green solid‐state lighting source in the 21st century, with the advantages of high efficiency, low energy consumption, good stability, long lifetime, and environmental protection 1–4 . Commercial WLEDs were usually based on GaN/InGaN chips coated with YAG: Ce phosphors and organic resin under blue light excitation to obtain white light 5–8 . As we all know, under high irradiation and high temperature conditions, organic resin or silicone with low thermal conductivity was easy to yellow and carbonize, resulting in reduced luminous efficiency (LE) and shortened life 9–13 .…”

“…[1][2][3][4] Commercial WLEDs were usually based on GaN/InGaN chips coated with YAG: Ce phosphors and organic resin under blue light excitation to obtain white light. [5][6][7][8] As we all know, under high irradiation and high temperature conditions, organic resin or silicone with low thermal conductivity was easy to yellow and carbonize, resulting in reduced luminous efficiency (LE) and shortened life. [9][10][11][12][13] Meanwhile, the serious reflec-tion would happen at the interface between the phosphor particle and the silicone matrix due to the large difference in refractive index, and the high scattering and reflective loss of the emission from the micro-sized phosphor layer also limited the conversion efficiency and luminous efficacy (LE).…”

Laser Synthesis of Cerium-Doped Garnet Nanoparticles

“…Blue-emitting LEDs with Ce-doped luminescent garnet phosphor nanopowders can be exploited to make white light, because of good blue light absorption, which is subsequently converted into yellow light [8]. The development of garnet-based LED devices can allow for better control of light scattering and the minimization of optical losses [9]. Garnet NPs can also be used for composite scintillation materials production in combination with such technologies as spin coating, thermal polymerization, chemical bath deposition, inkjet printing, 3D printing, and ceramization [7,10,11].…”