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: Er3+, Yb3+, Cr3+ 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: Er3+, Yb3+ nanoparticles can be modulated by the doping of the Cr3+ ions, the increase of the incident laser power and the change of the laser pulse-width. With the doping of the Cr3+ ions, the two green emissions decrease because of the energy transfer from the Er3+ states H211/2 and S3/24 to the Cr3+ 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 F9/24 of the Er3+ 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 H211/2 due to the small transfer rate from the Er3+ state H211/2 to the Cr3+ ions. The experimental results confirm that the concentration of the Cr3+ ions has less effect on the average life-time of the UC emissions at 524, 552, and 658 nm.