Host-to-activator energy-transfer efficiencies under vacuum ultraviolet excitation have been calculated for YBO 3 :Eu 3+ with particle sizes of 50À500 nm, using excitation and reflectance spectroscopy. The data were evaluated using published kinetic models in order to estimate the magnitude of energy lost to the surface of the particle as the crystallite size is decreased. The data indicate that surface losses become measurable at particle sizes of about 300 nm, whereas below about 100 nm, approximately 40% of the excitation energy is lost to the particle surface. The data did not allow us to draw any conclusions about the effect of particle size on the bulk transport of electronÀhole pairs.

No abstract