Effect of Tb³⁺ co-doping and particle size on K₂Ca₂(SO₄)₃:EU phosphor

Abstract

K₂Ca₂(SO₄)₃ doped with Eu, and co-doped with Tb were prepared by the solid state diffusion method. The nanoparticles of these phosphors were also prepared by the chemical co-precipitation method. The formation of the compounds was confirmed by XRD. The particle size was calculated by the broadening of the XRD peaks using Scherrer's formula. The particle size was found to be around 20 nm. Thermoluminescence (TL) was studied to see the effect of co-doping and particle size. Tb³⁺ co-doping decreases the intensity in the Eu²⁺ doped phosphor due to the energy transfer and multiple de-excitations through various radiative and non-radiative processes. The K₂Ca₂(SO₄)₃:Eu,Tb phosphor is found to be 0.33 times more sensitive than TLD-700H, but around 15 times more than LiF-TLD 100, and 7 times more than CaSO₄:Dy. The effective atomic number Z_eff is around 15, which is again comparable to CaSO₄:Dy.

However, very low sensitivity was observed in the case of nanoparticles. The decrease in the sensitivity is attributed to the particle size effect i.e., the volume-to-surface ratio. Study of photoluminescence (PL) of the material is also carried out.

Keywords:

• TLD phosphor
• K2Ca2(SO4)3:Eu,Tb, nanoparticles
• Co-doping
• Energy transfer

Acknowledgement

One of the authors (Numan) is very grateful to the Indian Council for the Cultural Relation (ICCR), India for financial assistance. We are also thankful to Dr. Amit Roy, the director of the Nuclear Science Centre (NSC), Delhi for permitting us to use the facilities at the centre.