Improvement in luminescence of thermally stable CaMoO4:Tb3+ green phosphor by Bi3+ ions

Abstract

The growing optoelectronic industries have prompted researchers to develop a single-component green phosphor for diverse applicability. It is well known that Tb3+ doped phosphors emit green light due to strong 5D4→7F5 transition. The green emission of Tb3+ ion can be enhanced by using sensitizers such as Bi3+ ion, which creates intermediate energy levels between the host and Tb3+, thereby, achieving efficient energy transfer between the host and Tb3+. In this article, we have reported a substantial improvement in the green emission of Tb3+ doped CaMoO4 by Bi3+ co-doping. The phosphors have been successfully prepared via a lucrative self-combustion process. The XRD patterns reveal an impurity-free tetragonal crystalline structure of all the phosphors. The Tb3+ doped CaMoO4 gives three major emissions at 489 nm, 544 nm and 621 nm corresponding to the Tb3+ transitions from 5D4 to 7F6, 7F5, and 7F3, respectively. The maximum emission has been achieved for 5% Tb3+ doped CaMoO4, which is further enhanced by 47% via co-doping of Bi3+. The improvement in emission intensity for Bi3+ co-doped phosphors is attributed to improved crystalline nature and transfer of energy from Bi3+ to Tb3+ levels. The energy transfer process from [MoO4]2- to Bi3+ and Tb3+ is explained in detail and maximum improvement is obtained upon co-doping of 4% Bi3+ ions. The incorporation of Bi3+ ions also results in shifting of CIE coordinates and color purity towards green color. The activation energy required for the thermal quenching is 0.25 eV, much better than already reported green phosphors. There is no change in the CIE coordinates of the overall emission with temperature indicating the better emission color stability of the phosphor. Hence with optimum concentration of Bi3+ and Tb3+ ion in CaMoO4 they can be used as potential green emitting phosphors.