White light upconversion in Yb-sensitized (Tm, Ho)-doped KLu(WO4)(2) nanocrystals: the effect of Eu incorporation

Monoclinic Yb-sensitized (Tm, Ho)-doped KLu(WO4)(2) nanocrystals of similar to 100 nm size have been synthesized by the modified Pechini sol-gel method. Their diode laser near-infrared (similar to 980 nm) excited upconversion emission properties have been characterized at power densities in the range 30-355 W cm(-2). Bright white light composed of blue similar to 475 nm, green similar to 540 nm, and red similar to 650 nm emissions, corresponding to Tm3+ (1)G(4) -> H-3(6), Ho3+ S-5(2), F-5(4) -> I-5(8), and Ho3+ F-5(5) -> I-5(8) electronic transitions, respectively, was generated by adjusting the Yb, Tm, and Ho contents in KLu(WO4)(2) nanocrystalline samples. Chromaticity coordinates of the emitted white light can be tuned by modifying the excitation power density. The effect of Tm and Ho on the luminescence dynamics has been described by analyzing the upconverted emission intensity dependence on the excitation power, as well as from Stokes and decay time measurements. The effect on upconversion properties of further codoping with Eu in these (Tm, Ho, Yb)-doped KLu(WO4) 2 nanocrystals has also been studied