COOPERATIVE LUMINESCENCE IN YTTERBIUM-DOPED CSCDBR3

Under near infrared excitation, ytterbium-doped CsCdBr3 exhibits a str ong blue luminescence due to a cooperative effect. The energy level sc heme of Yb3+ ions has been determined at low temperature by spectrosco pic measurements, allowing us to calculate the theoretical spectrum of the cooperative luminescence. The good agreement obtained with the ex perimental data confirms the process governing the anti-Stokes emissio n. We also present a comparison between theoretical and experimental c ooperative luminescence rates which is of particular interest because trivalent ions enter this lattice to form pairs of fixed structure. Th eoretical calculations of the cooperative luminescence probability are therefore much easier than in other compounds. The experimental coope rative rate constant is 0.13 s(-1), whereas the dipole-quadrupole and forced dipole-dipole interactions result in a theoretical rate constan t of approximately 0.70-1.6 x 10(-2) s(-1) for symmetric pairs and 0.7 6-1.7 x 10(-1) s(-1) for asymmetric ones. From a tentative estimation of asymmetric pairs concentration, we find a total cooperative rate co nstant between 2.2 x 10(-2) and 5.0 x 10(-2) s(-1). The agreement with experiment is considered to be reasonable since the radial integrals inserted in the theoretical calculations are not adjusted to experimen t.