The role of boron in phosphorescence persistence of rare-earth co-activated alkalai aluminates

Abstract

Nadir toprak elementleriyle (Eu, Dy) katkilandirilmis SrAl4O7(SA2ED) fosforlu tozlari Pechini teknigi kullanilarak sentezlenmistir. Eklenen boronun bu fosforlar uzerinde 2 etkisi oldugu tespit edilmistir: fosforışıllık suresinin uzamasi ve fazin saf bir sekilde elde edilmesini kolaylastirmasi. Sonuc itibariyle bu tezin amaci boronun SA2ED fosforlarina olan etkisinin arastirilmasidir. Degisen miktarlarda boron SA2 kristal yapisi icerisine, boronun kristal yapiya ve optik ozelliklere olan etkisinin arastirilmasi icin yerlestirilmistir X-isini kirilim spektralari gostermistir ki boron eklenmesi, 1000 oC'de kalsine edilen tozlarin fazlarinin saflasmasini kolaylastirmis, 1100 oC'de kalsine edilenlerde ise yeni bir S4A7 fazinin olusmasina sebep olmustur. Fosforışıllık suresi 5-30 mol % boron koyuldugunda 5 kata kadar artmaktadir. Gelisen optik ozelliklerin daha iyi anlasilabilmesi icin bant-arasi tuzak karakteristikleri termoluminesans ve fotoluminesans olcumleriyle arastirilmistir. Ayrica, yapi-ozellik iliskisinin kristal matriks icindeki boronun elektronik yapisi incelenerek anlasilabilmesi icin ELNES calismalari yapilmistir. ELNES bulgularinin nicel ve nitel analizleri ile boronun bolgesel bag kurmasi ve bunun kristal yapiya olan etkisine dair bilgi edinilmistir.

Rare-earth co-doped (Eu, Dy) SrAl4O7 (SA2ED) phosphor powders were synthesized by using a modified Pechini process. It has been noted that the addition of boron has two impacts on these phosphors?the persistence duration is extended, and the processing of phase pure powders is facilitated. Thus the objective of this thesis work is to investigate the effect of boron on SA2ED phosphors. Varying amounts of boron were incorporated into the SA2 lattice to investigate the effects on crystal structure and optical properties. X-ray diffraction spectra showed that boron addition enhances the phase purity of the powder at a calcination temperature of 1000 °C, whereas the formation of a new S4A7 phase was induced when a calcination temperature of 1100 °C was used. The afterglow duration was extended to longer than 5 hours when boron was present in 5-30 mol%. To elucidate the enhanced optical properties, interband trap characteristics were studied by thermoluminescence and photoluminescence. Moreover, to understand the structure-property relationship via investigating the electronic structure of the boron inside the crystal, ELNES studies were performed. With ELNES fingerprinting and quantitative analysis of the ELNES data, information on local bonding of boron and its effects on the crystal lattice were investigated.