Understanding of Luminescence Properties Using Direct Measurements on Eu2+‐Doped Wide Bandgap Phosphors. Issue 16 (18th May 2020)

• Record Type: Journal Article
• Authors: Amin, Muhammad Ruhul; Strobel, Philipp; Qamar, Amir; Giftthaler, Tobias; Schnick, Wolfgang; Moewes, Alexander
• Is Part Of: Advanced optical materials. Volume 8:Issue 16(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-05-18
• Subjects: DFT calculations -- Eu 2+‐doped phosphors -- optical luminescence -- optical transitions -- soft X‐ray spectroscopy; Optical materials -- Periodicals; Photonics -- Periodicals; 620.11295
• DOI: 10.1002/adom.202000504
• Languages: English
• ISSNs: 2195-1071

Abstract

Abstract: Recent developments in solid‐state lighting lead to a demand for new phosphors with excellent thermal stability, exhibiting large bandgaps for highly efficient emission. A detailed characterization of the luminescent material AELi2 Be4 O6 :Eu 2+ (AE = Ba, Sr) is presented using soft X‐ray absorption spectroscopy, X‐ray emission spectroscopy, X‐ray excited optical luminescence (XEOL) spectroscopy, and density functional theory (DFT) calculations. The experimental indirect bandgap for both BaLi2 Be4 O6 :Eu 2+ (BLBO:Eu) and SrLi2 Be4 O6 :Eu 2+ (SLBO:Eu) is found to be 6.5 ± 0.3 eV, which agrees well with the DFT calculations (6.8 eV for BLBO:Eu and 7.4 eV for SLBO:Eu). The crucial Eu 2+ 5d to conduction band energy separation is determined to be 0.21 ± 0.10 and 0.25 ± 0.10 eV for BLBO:Eu and SLBO:Eu, respectively, using resonant inelastic X‐ray scattering. These measured values are in good agreement with the thermal quenching measurements (0.20 ± 0.03 eV for BLBO:Eu and 0.26 ± 0.03 eV for SLBO:Eu). Finally, the XEOL measurement confirms the Eu 2+ 5d 1 4f 6 → 4f 7 transition, which is responsible for the ultranarrow band (full width at half‐maximum: 25 nm) blue optical luminescence at 455–457 nm for both compounds. With these measurements and calculations, deep insights are gained into the key properties of those two phosphors. Abstract : A detailed characterization of Eu 2+ ‐doped Be‐based phosphors is reported. It directly accesses important information on the electronic and optical properties of the materials such as the Eu‐intragap states and energy levels of all involved radiative processes. It also describes how the applied methods are helpful in design and understanding of new phosphor converted light‐emitting diode phosphors.