Tailored upconversion emission of Eu3+ in Sr2Ca(W,Mo)O6:Yb3+,Eu3+ by a laser via an electronic polarization mechanism

Abstract

The anomalous upconversion (UC) emission of the electric dipole transition ⁵D₀ → ⁷F₄ of Eu³⁺ ions at ∼690 nm can be tailored by a 976 nm laser beam in Sr₂Ca(W,Mo)O₆:Yb³⁺,Eu³⁺ samples at various pumping powers or temperatures, while the intensity ratio of the magnetic transition ⁵D₀ → ⁷F₁ at ∼594 nm to the electric dipole transition ⁵D₀ → ⁷F₂ at ∼612 nm barely changes. This is most probably attributed to the electronic polarization effect of the host materials with Mo on the electric dipole transition ⁵D₀ → ⁷F₄, which is proved by the larger dielectric permittivity of Sr₂CaMoO₆ compared to Sr₂CaWO₆ (10⁸ Hz), according to the alternating current (AC) impedance spectroscopy measurements and further evidenced by theoretical calculations of the dielectric function at high frequency (∼10¹⁴ Hz of the 976 nm laser light). The research gives an unusual perspective to tailoring the UC behavior of lanthanide ions through the electric field of a laser beam itself besides approaches of applying an external electric field, varying the chemical compositions, using different co-dopants, etc., which might be inspiring for the design of opto-electric multifunctional devices.