Bright orange and red light-emitting diodes of new visible light excitable tetrakis-Ln-β-diketonate (Ln = Sm3+, Eu3+) complexes

Abstract

The syntheses and luminescent properties of two new visible light excitable lanthanide complexes (NBu₄[LnL₄]) [L = 1-(4-(9H-carbazol-9-yl)phenyl)-4,4,4-trifluorobutane-1,3-dione; (Ln = Sm³⁺, Eu³⁺)] are described. The (NBu₄[LnL₄]) complexes exhibit bright photoluminescence at room temperature in solid state with characteristic red and orange emissions of Eu³⁺ and Sm³⁺ ions, respectively. Photoluminescent overall quantum yield (ϕ_ov) and lifetime (τ_obs) values obtained for the complexes are 80 ± 8%, 780 ± 6 μs for (NBu₄[EuL₄]) and 10% ± 1%, 97 ± 2 μs for (NBu₄[SmL₄]) (λ_ex = 410 nm) in solid state. RM1 calculations were employed for predicting the ground-state geometry of NBu₄[EuL₄], which shows that the central Eu³⁺ is 8-fold coordinated. Theoretical Judd–Ofelt and photoluminescence parameters predicted for NBu₄[EuL₄] from this model are in close agreement with the experimental values, proving the efficiency of this theoretical approach implemented in the LUMPAC software (http://lumpac.pro.br/theory). LEDs with the general structure ITO/PEDOT:PSS (50 nm)/(NBu₄[LnL₄]) (5%):CBP (66.5%)–OXD7 (28.5%) (50 nm)/BCP (50 nm)/LiF (1.5 nm)/Al (120 nm), using the two complexes as emitters were fabricated via a simple spin coating technique. The device based on (NBu₄[EuL₄]) exhibits the maximum brightness of 1234 cd m⁻², current efficiency of 3.5 cd A⁻¹, power efficiency of 1.3 lm W⁻¹ and external quantum efficiency of 2.3% with a pure red emission. Whereas, its Sm³⁺ analogue shows bright orange emission with a maximum brightness of 831 cd m⁻², current efficiency of 1.4 cd A⁻¹, power efficiency of 0.5 lm W⁻¹, and external quantum efficiency of 1.1%.