Enhanced upconversion emission and temperature sensor sensitivity in presence of Bi3+ ions in Er3+/Yb3+ co-doped MgAl2O4 phosphor

Mg0(.95-x)ErxYb0.05Al2O4 (x = 0.3, 0.5, 0.7, 1.0, and 1.5 mol%) and Mg(0.943-y)Er.007Yb0.05BiyAl2O4 (y = 2, 5, 7, 10, and 15 mol%) phosphor samples have been synthesized by solid state reaction method. The X-ray diffraction (XRD) measurements confirm the cubic phase formation and shift in peaks position due to Bi3+ ions doping. The surface morphology of the prepared samples has been studied by scanning electron microscopy (SEM) measurement. The FTIR spectra reveal the information about the vibrational bands arising due to different molecules or species/groups. The Mg(0.943-y)Er.007Yb0.05BiyAl2O4 phosphor sample gives an intense upconversion (UC) green emission peaks centered at similar to 521 and 543 nm due to (S-4(3/2), H-2(11/2))-> I-4(15/2) transitions and the weak red emission at 660 nm due to F-4(9/2)-> I-4(15/2) transition. The emission intensity of green bands is enhanced by 30 times and the red band by 10 times on addition of Bi3+ in Mg ((0.943)) Er0.007Yb0.05Al2O4 phosphor. This increase in emission intensity also enhances the fluorescence intensity ratio (FIR) of two thermally coupled levels emitting green radiation (i.e. FIR = I-521/I-543). The large variations of FIR with temperature clearly suggest that the material can be used as temperature sensor. The temperature sensing sensitivity is found to be quite high in presence of Bi3+ ions. The laser induced optical heating with pump power has also been observed in this material.