Upconversion emission of BaTiO<SUB>3</SUB>: Er nanocrystals

Here, we report the dopant concentration and pump-power dependence upconversion emission properties of erbium doped BaTiO<SUB>3</SUB> nanocrystals derived from sol-emulsion-gel method. Green (550 nm) and red (670 nm) upconversion emissions were observed at room temperature from the ⁴S_3/2 and ⁴F_9/2 levels of Er<SUP>3+</SUP>: BaTiO<SUB>3</SUB> nanocrystals. It is found that at 850 mW of cw excitation power (at 980 nm) the total luminescence was 17130 Cd/m<SUP>2</SUP> for 1000°C heated 0.25 mol% Er-doped BaTiO<SUB>3</SUB> nanocrystals. It is worthwhile to mention that the unusual power-dependent upconversion luminescence (saturation) is observed at higher dopant concentration (2.5 mol%) and high pump power. Our analysis confirms that the depletion of the excited state is responsible for the relevant fluorescence upconversion. We have again confirmed that a twophoton excited state absorption process occurs for all samples