CaMoO4: RE3+, Yb3+, M+ phosphor with controlled morphology and color tunable upconversion

Abstract CaMoO 4 :RE 3+ ,Yb 3+ (RE = Er, Ho, Tm) phosphors were successfully synthesized by a facile hydrothermal method. XRD patterns confirmed tetragonal structure under different RE 3+ and M + ions doping conditions. Particles shapes and sizes were confirmed by SEM and TEM analyses. Particles shape and size were well tuned by control of solution pH; spherical balls consisting of nano-grains at low pH of ∼2, rice grain shapes at moderate pH of ∼6, and thin flakes at higher pH of ∼12, were observed. Fine tunability of upconversion (UC) emission color was achieved by doping multiple RE 3+ ions within a single CaMoO 4 host. Blue, green and orange upconverted emission were observed by doping Tm 3+ , Er 3+ and Ho 3+ in the CaMoO 4 , respectively. Further, the emission colors were well tuned by the combination of Tm, Er and Ho ions and their concentrations. CaMoO 4 :Tm 3+ ,Ho 3+ ,Yb 3+ exhibited perfect white emission with well tunability from cool white to warm white colors. Substitution of part of Ca ions by M + (M = Li, Na, K, Rb) ions affected the crystal field symmetry around RE 3+ ions and hence changed the transition probabilities between their f–f transition levels, consequently intensified the UC intensities. The blue (Tm 3+ ), green (Er 3+ ), and orange (Ho 3+ ) upconversion intensities of CaMoO 4 :RE 3+ ,Yb 3+ ,0.10 K + phosphors increased by 60, 50 and 40 folds compared to the unsubstituted analogues, respectively. The K substituted CaMoO 4 :RE 3+ ,Yb 3+ ,K + phosphors exhibited intense UC emissions visible by naked eye even pumped by less than 1 mW laser power and can have potential application in displays and variety of other applications.