Enhanced upconversion and downshifting emissions from Tm3+, Yb3+ co-doped CaZrO3 phosphor in the presence of alkali ions (Li+, Na+ and K+)

Abstract

The Tm3+, Yb3+ co-doped CaZrO3 phosphor samples have been synthesized through solid state reaction method in the absence and presence of alkali metal ions (i.e. Li+, Na+, K+). The X-ray diffraction (XRD) study shows the formation of CaZrO3 crystal with orthorhombic phase. The Tm3+, Yb3+ co-doped CaZrO3 phosphor emits intense upconversion emission in blue (474 nm) and NIR (799 nm) regions due to 1G4 → 3H6 and 3H4 → 3H6 transitions of Tm3+ ions, respectively on excitation with 980 nm radiation. The emission intensity is significantly enhanced in the presence of alkali ions due to charge compensation and asymmetry in the crystal field. The emission intensity in the case of Na+ co-doped phosphor is maximum and at 1 W pump power, it is increased by ∼44 and ∼31 times in blue and NIR regions, respectively as compared to without alkali ions co-doped phosphor. The downshifting emission in blue region has been observed due to oxygen vacancy and Tm3+ ions on excitation with 277 and 360 nm radiations which is enhanced significantly in the presence of alkali ions. Thus, the intense blue emission by this material is suitable for blue and white light emitting phosphors.