Energy transfer processes in lanthanide doped oxide materials for innovative optical technologies

 

Marco Bettinelli

 

Luminescent Materials Laboratory, Department of Biotechnology University of Verona, and INSTM, UdR Verona, Verona, Italy; email: marco.bettinelli@univr.it

 

        Luminescent materials have the ability to emit electromagnetic radiation following suitable excitation processes. In particular, the luminescence can be excited using different energy sources, such as photons (photoluminescence), an electron beam (cathodoluminescence), a voltage (electroluminescence) and others. In the last years luminescent inorganic materials have gained increasing technological importance. Nowadays, in fact, this class of materials finds numerous applications, e.g. as phosphors for lighting devices and cathode ray tubes, X- and gamma-ray scintillators, electroluminescent phosphors for display devices, light emitting diodes, optical fiber amplifiers, solid state lasers, security markers, persistent phosphors and materials for biomedical optical applications. A large part of these technologies are based on inorganic hosts containing lanthanide (rare earth) ions as emitting centres. This is due to the fact that lanthanide ions can emit very efficiently in the UV-visible-IR regions with decay times in a wide range from nanoseconds to milliseconds.

         It is remarkable that some important applications depend on or are enhanced by processes in which the excitation energy is captured by suitable sensitizers and is transferred in an efficient way to the activator ions which then decay by emitting photons. Despite numerous studies over the years, these energy transfer processes are still extremely interesting from both a fundamental and an applied point of view, as transfer processes in pairs of ions and from the host to luminescent ions are crucial for development of innovative phosphors for lighting, and scintillators able to convert high energy radiation to visible (or UV) light, making detection much easier.

        In this talk I will present as examples of these transfer processes some recent results coming from the research carried out in my laboratory in Verona. Firstly, I will describe and discuss results obtained on oxide materials activated with the Pr³⁺ ion, which gives rise to allowed and strong d-f luminescence in the near UV region upon high energy excitation, as a consequence of an energy flow from the host to the dopant ions. These materials show potential for application in the field of gamma-ray detectors for Positron Emission Tomography (PET), an important medical diagnostic technique. Secondly, I will present results obtained on oxide hosts based on the Tb³⁺ ion and containing Eu³⁺ as an activator. In these materials, both excitation in the X-ray region and in the UV-visible originates efficient red emission from Eu³⁺, due to energy flow from the host and/or transfer from Tb³⁺ to Eu³⁺. This behaviour shows that this class of materials has potential applications in the fields of both scintillators and phosphors for LED lighting.