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We have investigated the spectroscopic properties of praseodymium ion in a Y3Al5O12 sample. We obtained the luminescence spectra by exciting selectively the sample at 460 and 599nm, resulting in the excitation of the P03 and D21 levels, respectively. With excitation in the P03 level we obtained emission from this level and from the D21 level. We used time resolved spectra and decay pattern inspection to assign spectral lines to specific radiative transitions. With excitation in the D21 level we observed luminescence emitted by the same level and upconverted emission from the P03 level and the (4f5d) band. The experimental data indicate that the mechanism responsible for the upconversion processes is excited state absorption. We found the upconverted emission from P03 and the (4f5d) band to be proportional to the square of the excitation energy and to the cube of the excitation energy, respectively.

Ion-ion upconversion excitation of the 4f5d configuration in Pr:Y 3 Al 5 O 12 Experiments and Förster theorybased rate equation modelWe exploit the upconversion process, utilizing it as a sensitive tool in site-selective spectroscopy of rare earth ion-doped solids. In the Y 3 Al 5 O 12 :Pr 3+ praseodymium-doped yttrium aluminum garnet ͑YAG: Pr͒ crystals the Pr ions are situated in sites having slightly different environments. Under pulsed excitation into the 1 D 2 level, the upconverted emission from the 3 P 0 level of each Pr subsystem exhibits its unique, and easily identifiable, response to pulsed excitation, simplifying the process of selectively exciting ions in different sites. Using this technique, we have been able to identify three different sites in a sample of YAG with Pr concentration of 0.5%. We present the physical reasons for the sensitivity of this technique as an example of a useful approach to distinguish among atomic systems residing in slightly dissimilar environments.

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