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 ⁴S_3/2 and ⁴F_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 (²H_11/2 & ⁴S_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.