Synthesis of Sr2Si5N8:Ce3+ phosphors for white LEDs via efficient chemical vapor deposition

Abstract

Novel chemical vapor deposition (CVD) process was successfully developed for the growth of Sr2Si5N8:Ce3+ phosphors with elevated luminescent properties. Metallic strontium was used as a vapor source for producing Sr3N2 vapor to react with Si3N4 powder via a homogeneous gas-solid reaction. The phosphors prepared via the CVD process showed high crystallinity, homogeneous particle size ranging from 8 to 10 μm, and high luminescence properties. In contrast, the phosphors prepared via the conventional solid-state reaction process exhibited relative low crystallinity, non-uniform particle size in the range of 0.5–5 μm and relatively lower luminescent properties than the phosphors synthesized via the CVD process. Upon the blue light excitation, Sr2−xCexSi5N8 phosphors exhibited a broad yellow band. A red shift of the emission band from 535 to 556 nm was observed with the increment in the doping amount of Ce3+ ions from x = 0.02 to x = 0.10. The maximum emission was observed at x = 0.06, and the external and internal quantum efficiencies were calculated to be 51% and 71%, respectively. Furthermore, the CVD derived optimum Sr1.94Ce0.06Si5N8 phosphor exhibited sufficient thermal stability for blue-LEDs and the activation energy was calculated to be 0.33 eV. The results demonstrate a potential synthesis process for nitride phosphors suitable for light emitting diodes.

Facile synthesis and spectroscopic characterization of siliconitride phosphors for white light‐emitting diodes

“…In the CVD process, initially Sr 3 N 2 is formed via the reaction between strontium metal and nitrogen gas and it transforms into Sr 3 N 2 vapor. Sr 3 N 2 vapor then flows to react with Si 3 N 4 and Eu 2 O 3 mixtures, resulting the formation of phosphors with narrow size distribution …”

“…Sr 3 N 2 vapor then flows to react with Si 3 N 4 and Eu 2 O 3 mixtures, resulting the formation of phosphors with narrow size distribution. 8,9 The upper inset of Figure 1 illustrates the photoluminescence spectra of Sr 1.98 Eu 0.02 Si 5 N 8 phosphors. The photoluminescence intensity of phosphors prepared via the CVD method was approximately 35% higher than that prepared via the solid-state route owing to the high crystallinity and large particle size of the prepared phosphors.…”

“…Sr 2 Si 5 N 8 :Ce 3+ , Eu 2+ (SSN) phosphors were prepared via the modified CVD process described in our previous research. 8 The raw materials Si 3 N 4 , CeO 2 , and Eu 2 O 3 were mixed and this mixture was put along with strontium metal in two molybdenum crucibles separately. The precursor was annealed at 800°C for 1 hour in a reducing atmosphere (10 vol% H 2 and 90 vol% N 2 ) for nitridization.…”

“…7 Therefore, a modified chemical vapor deposition (CVD) process was developed to synthesize Sr 2 Si 5 N 8 phosphors. 8 In the present CVD approach, metallic strontium was used to form Sr 3 N 2 vapor and the vapor was allowed to react with solid Si 3 N 4 and rare-earth chlorides. The gas-solid reaction helped to enhance the homogeneity of reaction.…”

Eu3+-activated La2MoO6-La2WO6 red-emitting phosphors with ultrabroad excitation band for white light-emitting diodes

“…By virtue of admirable advantages of long working lifetime, energy saving, low cost, high luminous efficiency and environmental compatibility, the phosphor-converted white light-emitting diodes (WLEDs) which are considered as the next-generation illumination sources to supersede the conventional fluorescent lamps have been extensively used in indoor lighting, automobile displays and flashlights 1–5 . Presently, the commercial WLEDs which are made up of a blue-emitting InGaN LED chip and Y 3 Al 5 O 12 :Ce 3+ yellow-emitting phosphors suffer from poor color rending index (CRI ~ 70–80) and high correlated color temperature (CCT ~ 7000 K) as a result of inefficient red emission component 6–8 .…”