Enhancement of upconversion, temperature sensing and cathodoluminescence in the K+/Na+ compensated CaMoO4:Er3+/Yb3+ nanophosphor

Abstract

Charge compensated alkali metal ions (Na+, K+) codoped CaMoO4:Er3+/Yb3+ nano-flakes were synthesized via a hydrothermal method. The effect of doping concentration of Na+ and K+ ions on upconversion luminescence in CaMoO4:Er3+/Yb3+ was investigated with respect to its dependence on input pump power and external temperature using 980 nm laser light excitation. Simultaneous incorporation of K+/Na+ into CaMoO4:Er3+/Yb3+ showed 36 and 5 times enhancements in green and red emission intensities, which were explained in terms of charge compensation and lifetime variation in the S-4(3/2) and F-4(9/2) levels of Er3+ ions. A high thermal sensitivity of the material was realized with K+/Na+ incorporation using the fluorescence intensity ratio technique of two thermally coupled energy levels (H-2(11/2) & S-4(3/2)) of Er3+. The temperature sensitivity was enhanced by four times by K+/Na+ codoping with a maximum sensitivity of 0.0216 K-1 at 490 K. Additionally, the cathodoluminescence properties of the material as a function of filament current and accelerating voltage were also explored and showed enhanced luminescence, which is suitable for field emission display device applications. The results show that simultaneous codoping of K+/Na+ in CaMoO4:Er3+/Yb3+ is a very effective way to integrate this material for advanced photonic applications.