Valencies of Eu in CaS:Eu, La

✍ Scribed by Han Choi; Chang-Hong Kim; Chong-Hong Pyun; Sung-Jin Kim

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 255 KB
• Volume: 138
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1998.7766

✦ Synopsis

Photoluminescence of La and Eu codoped CaS prepared in sodium and potassium polysulfide flux was studied. The emission spectra of CaS : Eu prepared in both fluxes show a broad band at 650 nm due to the f-d transition of Eu 2؉ . When potassium polysulfide flux is used, the emission from Eu 2؉ decreases and the line emission of Eu 2؉ appears with concentration of codoped La 3؉ . However, when sodium polysulfide flux is used, clear line emission spectra of Eu 3؉ were observed, in addition to the broad band spectrum from recombination process of defects and vacancies in the host matrix. For the first time at room temperature, sharp line spectrum of Eu 3؉ is observed and this is a strong indication of La 3؉ -Eu 3؉ pairing in CaS : Eu, La. EPR intensity of Eu 2؉ increases with Eu concentration and decreases with La 3؉ concentration in CaS : Eu, La prepared in potassium polysulfide flux. However, the result of EPR study suggests that only Eu 3؉ is doped when CaS : Eu, La is prepared in sodium polysulfide flux.