An efficient blue phosphor Ba2Lu5B5O17:Ce3+ stabilized by La2O3: Photoluminescence properties and potential use in white LEDs

We demonstrate a blue emitting Ba2(Lu0.98La0.02)5B5O17:Ce3+ (BLLB:Ce3+) phosphor prepared by high-temperature solid-state reaction. The pure phase of Ba2Lu5B5O17 is difficult to obtain. To stabilize the crystal structure of Ba2Lu5B5O17, the larger ion radius of La3+ was added to substitute Lu3+ in raw materials. It is found that pure-phase Ba2Lu5B5O17 is successfully obtained by adding 2% La3+. Upon 348 nm excitation, a luminescence internal quantum efficiency of BLLB:Ce3+ can reach as high as 92%, which is comparable to the commercial blue phosphor BaMgAl10O17:Eu2+. The BLLB:Ce3+ phosphor shows a blue emission band peaked at 443 nm with a main excitation band peaked at 348 nm. The dependence of luminescence intensity on Ce3+ concentration was studied. The maximal luminescence intensity was observed at 1% Ce3+, which gives a critical distance of 2.41 nm between two Ce3+ ions for luminescence quenching. The emission of the present phosphor is stable with increasing temperature up to its quenching temperature of 403 K. A white light emitting diode (WLED) was fabricated based on a near UV LED chip coated with a blend of the present blue phosphor, the commercial green (Ba,Sr)2SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors. The WLED exhibited a low correlated color temperature of 4356 K with a high color rendering index of 93.2. These results suggest that BLLB:1% Ce3+ can be utilized as a blue phosphor in UV based WLEDs.