Host dependent upconversion of Ho³⁺ activated system for extended luminescence color tunability and highly-sensitive optical thermometry

The design of color-tunable upconversion luminescence for expand the application of optical fields has been a hot research topic. Herein, Yb³⁺, Ho³⁺ co-doped YNb_1-xV_xO₄ (x = 0, 0.25, 0.5, 0.75, 1) are synthesized by solid state method. The color tunability of UC luminescence from green to red is achieved by varying the component ratio of Nb⁵⁺ and V⁵⁺ in the mixed compositions. The continuous introduction of V⁵⁺ component strengthens the vibrational band of the mixed host, thus promoting the non-radiative relaxation of ⁵I₆→⁵I₇ in activator Ho³⁺, which becomes the key to obtain the color-tunable UC luminescence. Besides, the Ho³⁺ activated system exhibits strong temperature dependent variation in UC luminescence intensity of ⁵F₄/⁵S₂→⁵I₈ and ⁵F₅→⁵I₈. The optimal sensitivity parameters can be obtained as 35.64 × 10⁻³ K⁻¹ for S_A-max and 3.78 % for S_R-max in YVO₄:Yb³⁺,Ho³⁺ thermometer. Benefit by the luminescence color tunability and excellent thermometry performance, phosphors with host dependent upconversion of Ho³⁺ activated system are expected to achieve optical applications in various fields of anti-counterfeiting, display, and temperature sensing.