Novel strategies to tune the color emission of Bi2Ti2-xZrxO7:Er3+,Yb+3 upconversion phosphors: Substituting Ti by Zr and annealing at high temperatures

Abstract

Bi2Ti2-xZrxO7:Er3+,Yb3+ phosphors were synthesized with different content of Zr (X = 0–1.5) by combustion method at 550 °C, producing a mixture of Bi2Ti2O7/Bi4Ti3O12 phases. After increasing the synthesis temperature to 1000 °C, a pure Bi2Ti2O7 (BiTiO) phase was obtained as well as porous coalesced microparticles (2–10 µm) with pore sizes of 110–420 nm. Those samples produced green (548 nm)/red (655 nm) and NIR (1530 nm) emission bands after excitation with 980 nm and their color emission was tuned from green to yellow–red or viceversa using two strategies: i) by increasing the Zr content in the Bi2Ti2-xZrxO7:Er3+,Yb3+ host (from X = 0 to 1) or ii) by increasing the synthesis temperature from 550 to 1000 °C. Interestingly, the intensity of the NIR and red emission bands was enhanced with the content of OH groups on the surface of the BiTiO:Yb,Er phosphors.