Despite the concentrated research of ZnO, this material still has several new opportunities for biological and medical applications as luminescence markers and drug delivery systems, and optoelectronic applications as a phosphor material.

Several systems are studied for above applications. Lately, interest focused on properties of rare-earth (RE) doped nanoparticles. This relates to their attractive light emission properties – mainly due to observation sharp atomic-like 4f-4f emission lines.

The main limitation for a wider use of RE doped materials is difficulty of 4f-4f excitation

upon a host lattice excitation. This is why 4f-5d or charge transfer excitations are used,

limiting selection of host materials.

In some cases this problem can be avoided by using codoped oxide nanoparticles. In the

present work we report that ZnO nanoparticles doped with selected RE ions, such as: Pr, Tb,Eu and codoped with Al show efficient 4f-4f emission excited upon host excitation. This makes this system very attractive for different above-mentioned applications. Detail results are shown for Eu doped nanoparticles. Based on photoluminescence investigations the chromaticity diagrams are also calculated.

In this work we analyze optical properties of ZnO:10%Eu nanopowders obtained by a hydrothermal method. Effects of annealing on CL and PL spectra is investigated. The observed CL and PL changes are related to the reduction of OH-groups on the surface of annealed samples. Typical Eu 3+ emissions, related to ⁵D₀ to ⁷F₁, ⁷F₂, ⁷F₃ and ⁷F₄, transitions, are detected for ZnO:10%Eu nanopowder only after annealing at 750^oC. Chromaticity parameters of the emission are calculated.

The research was partially supported by the National Science Centre project 20/0139/N/ST3/04189

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