Brilliant Nonlinear Optical Response of Ho(3+) and Yb(3+) Activated YVO(4) Nanophosphor and Its Conjugation with Fe(3)O(4) for Smart Anticounterfeit and Hyperthermia Applications

[Image: see text] YVO(4):Ho(3+)/Yb(3+) nanophosphors prepared by an effective polyol-mediated route show dual-mode behavior in photoluminescence. Upon 980 nm excitation, the upconversion red emission spectrum exhibits a bright red peak at ∼650 nm, characteristic of the electronic transition of the Ho(3+) ion via involvement of two-photon absorption, which has been confirmed by the power-dependent luminescence study. Moreover, at 300 nm excitation, downconversion emission peaks are observed at 550, 650, and ∼755 nm. The nonradiative resonant energy transfer occurs from the V–O charge transfer band to Ho(3+) ions, resulting in an improved emission of Ho(3+) ions. Moreover, polyethylene glycol-coated nanoparticles make it suitable for water dispersibility; and these particles are conjugated with Fe(3)O(4) nanoparticles to form magnetic–luminescent hybrid nanoparticles. Highly water-dispersible magnetic–luminescent hybrid material attained the hyperthermia temperature (∼42 °C) under an applied AC magnetic field. The specific absorption rate value is found to be high (138 W/g), which is more than that of pure superparamagnetic Fe(3)O(4) nanoparticles. At 300 nm excitation, the high quantum yield value of ∼27% is obtained from YVO(4):Ho(3+)/Yb(3+), which suggests that it is a good phosphor material. By employing the neutron activation analysis technique, it is shown that nanophosphor particles can absorb Au(3+) up to the ppm level. Interestingly, such nanophosphor also shows the potentiality for anticounterfeiting applications.