Cooling in Er3+:BaMoO4 phosphor on codoping with Yb3+ for elevated temperature sensing

Abstract

The tetragonal BaMoO4 phosphors having scheelite structure codoped with Er3+-Yb3+ have been synthesized by chemical co-precipitation method. The cooling on codoping with Yb3+ in Er3+ doped BaMoO4 phosphor has been achieved under excitation at 808nm CW diode laser. The pump power density dependence fluorescence intensity ratio (FIR) variation study shows that the FIR remains almost constant (FIR=1.2) as the pump power density increases from 6.49W/cm2 to 72.07W/cm2. For FIR=1.2 the calculated temperature is observed to be ∼270K which is lower than the room temperature. This shows that the presence of the Yb3+ ions upto certain extent in the codoped phosphor causes cooling effect around the Er3+ ions. This is basically due to the back energy transfer from the Er3+ to Yb3+ ions. The cooling efficiency of the prepared phosphor is found to be ∼80.97%. The phosphors codoped with Yb3+ ions up to 2.0wt% do not show optical heating, whereas the strong optical induced heating is observed in the Er3+ singly doped phosphor. As the concentration of the Yb3+ is increased above 2.0wt% the codoped phosphor starts showing optical heating. The temperature dependent study performed at high pump power density (72.07W/cm2) for the codoped phosphor reveals that the phosphors codoped with Yb3+ ions, where the optical heating is not observed (i.e., cooling is observed), shows temperature sensing behaviour and hence may be suitable for high temperature sensing with better sensitivity.