Effects of Fluxes on Luminescence Properties of Ca3(ScZn)2Si3O12:Ce3+ Green Phosphor for White LEDs

Abstract

Carbothermal reduction (CTR) method was used to synthesize several samples series; flux added into Ca2 955Sc1 8Zn0 3Si3O12:0 03Ce3+ (CSZS:Ce) Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu2+ Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu3+ and Ca2 955Ga2Si3O12:0 03Ce3+ (CGS:Ce) Different kind of fluxes; LiF NaF LiF-NaF and NH4Cl fluxes were added into Ca2 955Sc1 8Zn0 3Si3O12:0 03Ce3+ (CSZS:Ce) separately We used Eu2O3 as an activator source and NaF flux in solid state reaction and carbothermal reduction method to form Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu3+ and Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu2+ respectively Another sample series were prepared by substituted Sc3+ ions by Ga3+ ions to form Ca2 955Ga2Si3O12:0 03Ce3+ Doped Zn2+ and NaF flux also were used to form Ca2 955Ga1 8Zn0 3Si3O12:0 03Ce3+ series By adding 2 wt% of NaF flux into CSZS:Ce can enhance the PL intensity and quantum efficiency as high as CSZS:Ce without flux Besides can reduce the sintering temperature up to 300 oC compared to former CSZS:Ce without flux However the thermal quench tend to decrease more for CSZS:Ce with flux In addition NH4Cl flux has a negative effect at low temperature of sintering process due to many impurities can be detected from XRD LiF-NaF compound flux exhibit a single phase at relative low sintering temperature 1150 oC only by using 1 wt% of compound flux From XRD pattern both Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu2+ and Ca2 955Sc1 8Zn0 3Si3O12:0 03Eu3+ with 2 wt% of NaF showed a good crystallinity at 1150 oC Replacing activator Ce3+ ions by Eu2+ or Eu3+ ions has significant effect specially on emission wavelength of phosphor According UV/Visible spectra CSZS:Eu2+ can be excited by UV light and visible light (green) A weak emission can be observed from UV light excitation but no emission detected in visible light region from green light excitation (520 nm) CSZS:Eu3+ show weak emission between 580-640 nm Compared with Ca2 955Sc1 8Zn0 3Si3O12:0 03Ce3+ (CSZS:Ce) series Ca2 955Ga2Si3O12:0 03Ce3+ (CGS:Ce) series were not matched well with XRD database pattern Ca3Ga2Si3O12 JCDPS# 74-1576 However many impurities detected such Ca2Ga2SiO7 and Ca2SiO4

Date of Award	2014 Aug 24
Original language	English
Supervisor	In-Gann Chen (Supervisor)