Amitava Patra

We investigated the frequency upconversion (UC) process in BaTiO₃:Er³⁺ nanocrystals for excitation wavelengths in the range 638 to 660 nm. Green upconversion emissions at 526 and 547 nm corresponding to ²H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 to transitions of the Er³⁺ were observed. The excitation spectrum for UC emissions presented three bands, due to ground state and excited state absorption of Er³⁺ ions. The UC intensity as a function of the laser power was investigated and it was found this a two-photon absorption process.

The effect of dopant concentration on the blue upconversion (UPC) emission of Tm³⁺ -doped ZrO₂ nanocrystals under different excitation wavelengths in the red region is reported. The UPC emissions are due to the f−f electronic transitions from excited states ¹G₄ and ¹D₂ of Tm³⁺. We observed a chromatic change in the UPC with tuning the excitation wavelength. The UPC emission bands at 475, 488, and 501 nm are observed under excitation at 649 nm, but bands centered at 454 and 460 nm are observed when the excitation wavelength is tuned to 655 nm. The UPC emission could be tuned from 501 to 454 nm (∼47 nm) by changing the excitation wavelength from 649 to 655 nm (∼6 nm). The pump power dependence of the emission bands at 475, 488, and 501 nm were investigated on excitation intensity at 649 nm, and the emission bands at 454 and 460 nm are investigated on excitation intensity at 655 nm, which confirms that all of these UPC emission lines are a two-photon absorption process.