Upconversion emission and its color modulation of the YVO₄: Er³⁺, Yb³⁺, Cr³⁺ nanoparticles

With the excitation of a 978 nm laser, the upconversion (UC) emissions of the YVO₄: Er^3þ, Yb^3þ, Cr^3þ nanoparticles include three emission bands located at 524, 552 and 658 nm, respectively. The UC emission characterization confirms that the UC emission of the YVO₄: Er^3þ, Yb^3þ nanoparticles can be modulated by the doping of the Cr^3þ ions, the increase of the incident laser power and the change of the laser pulse-width. With the doping of the Cr^3þ ions, the two green emissions decrease because of the energy transfer from the Er^3þ states ²H₁₁∕₂ and ⁴S₃∕₂ to the Cr³þ ions. With the increase of the incident laser power, the two green emissions increase due to the decrease of the transfer rate of the energy transfer path to the state ⁴F₉∕2 of the Er^3þ ions. With the increase of the incident laser pulse-width from 0.2 to 6 ms the intensity ratio of the emission at 524 nm to the emission at 658 nm increases from 0.063 to 0.19, which is due to the number accumulation at the state ²H₁₁∕₂ due to the small transfer rate from the Er^3þ state ²H₁₁∕₂ to the Cr^3þ ions. The experimental results confirm that the concentration of the Cr^3þ ions has less effect on the average life-time of the UC emissions at 524, 552, and 658 nm.