Luminescence studies on doped borates, A₆MM'(BO₃)₆

Abstract

Select compounds of the new hexaborates of the type A₆MM'(BO₃)₆ have been synthesized by the solid state reaction and are subjected to photoluminescence studies after due characterization by powder XRD, density, TG/DTA, IR and Diffuse reflectance spectroscopy. The results of investigations on the photoluminescence of the compounds of the type, Sr₆EuM'(BO₃)₆ with A=Sr; M=Eu; M'=Al, Ga, In; LaSr₅MM'(BO₃)₆: Eu with A=La, Sr; MM'=YMg, ScMg, MgAl; SmSr₅YMg(BO₃)₆, Sr₆MAl(BO₃)₆ with M=Gd, Dy; Sr₆YAl(BO₃)₆: Bi, Pb; and La₂Sr₄SrMg(BO₃)₆: Pb, are presented here. A new compound EuSr₅YMg(BO₃)₆ has also been synthesized and studied. The luminescence features of Eu, Sm, Gd, Dy, Bi (all 3+) and Pb²⁺ ions are discussed. Red emission by Eu³⁺ ion doped both at the A and M sites have been studied at low and high Eu³⁺ concentrations and the data analysed with respect to the site occupancy and the possible site disorder. The positions of the emission lines depend not only on the site occupancy but also on the ions present at the M' site. The variation in Eu³⁺ emission intensity with its concentration reveals a near-saturation behaviour, as evidenced by studies on La_1-xEu_xSr₅YMg(BO₃)₆ (x=0.05-1.0). The Pb²⁺ ion exhibits efficient violet luminescence under 254 nm excitation. The results establish that these hexaborate compounds are excellent hosts for the high efficiency room temperature luminescence of the lanthanide (Eu, Sm, Gd, Dy) and Bi, Pb ions.