LUMINESCENCE PROPERTIES OF (LA,PR)(2)TI2O7

The luminescence properties of the pyrotitanates (La,Pr)(2)Ti2O7 are e xamined as a function of the Pr3+ concentration in the range 0.2-15 mo l% Pr. Under UV excitation at 337 nm, the compounds exhibit intense lu minescence signals due to praseodymium arising mainly in the blue and in the red region of the spectrum. The red emission is due essentially to Pr D-1(2)-->H-3(4) transitions and appears to be the more intense in the lowest Pr-concentrated compounds. In contrast, the blue lumines cence (Pr P-3(0)-->H-3(4) transitions) is predominant in the highest P r-activated titanates. This behaviour is explained by considering two distinct categories of sites inside which the Pr3+ ions undergo crysta l field effects of different strengths. (C) 1998 Elsevier Science S.A.