Tm(3+); Yb(3+):Zn(2)TiO(4) near infrared to blue upconversion phosphors for anti-counterfeit applications

Tm(3+); Yb(3+):Zn(2)TiO(4) samples have been synthesized using a solid state reaction route. The phase, lattice parameters, crystallite size has been examined using X-ray Diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). An intense peak of Yb(3+) codoped samples is observed near ∼957 nm due to the (2)F(7/2) → (2)F(5/2) transition in diffuse reflectance spectra (DRS), which confirms the presence of Yb(3+) ion in the prepared compound. The optical band gap of Yb(3+) codoped samples has been calculated using Kubelka–Munk function. The Raman spectra corresponds to incorporation of Tm(3+)/Yb(3+) at the octahedral and tetrahedral site of the spinel host. The emission spectra recorded by using 370 nm excitation wavelength shows intense blue colour band corresponding to the (1)G(4) → (3)H(6) transition of Tm(3+) ion. The upconversion (UC) emission spectra recorded by using 980 nm laser excitation source shows emission bands due to the (1)G(4) → (3)H(6), (1)G(4) → (3)F(4) and (3)H(4) → (3)H(6) transitions of Tm(3+) ion in the host matrix lying in the blue, red and NIR regions respectively. There is effective enhancement of about ∼35 times in the blue UC emission intensity with incorporation of Yb(3+) at 3% doping concentration in the prepared sample. The anti-counterfeit application of the optimized upconverting phosphor has been successfully demonstrated.