Ca[B8O11(OH)4] : Eu2+ – A Highly Efficient Deep Blue‐Emitting Phosphor Prepared by Low‐Temperature Self‐reduction

• Published in: Chemistry : a European journal 2021-10, Vol.27 (55), p.13819-13827
• Main Authors: Liang, Pan, Lian, Wen‐Li, Liu, Zhi‐Hong
• Format: Article
• Language: English
• Subjects: blue-emitting phosphor; calcium borate; Chemistry; Color; Color temperature; Crystal structure; Europium; Excitation spectra; high quantum yield; Light emitting diodes; low-temperature self-reduction; Luminescence; Luminous efficacy; Luminous intensity; Morphology; Phosphors; Photoluminescence; Photons; Quantum efficiency; Raw materials; Reduction; ultra-high color purity; Ultraviolet radiation; White light
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202101639

Highly efficient inorganic phosphors are crucial for solid‐state lighting. In this paper, a new method of low‐temperature self‐reduction was used for preparing a highly efficient deep blue‐emitting phosphor of Ca[B8O11(OH)4] : Eu2+ (CBH : Eu2+). The crystal structure, morphology, chemical state, and photoluminescence (PL) properties of the CBH : Eu2+ phosphor have been investigated. By using the screened hybrid function (HSE06), the band gap (Eg) of CBH was calculated to be 7.48 eV, which is a necessary condition for achieving high quantum yield phosphors. The experiment results show that almost all the added raw materials of Eu3+ can be reduced to Eu2+ in CBH crystal under a non‐reducing atmosphere. The CBH : Eu2+ phosphor shows a broad excitation spectrum centered at 277 and 327 nm in the range of 220 to 400 nm, and a narrow‐band emission spectrum centered at 428 nm in the range of 400 to 500 nm, with a full width at half maximum (fwhm) of 42.35 nm. Under UV radiation, the CBH : 2 %Eu2+ exhibits high photoluminescence quantum yield (PLQY=95.0 %), high external quantum efficiency (EQE=31.1 %), and ultra‐high color purity (97.6 %). The PL intensity of CBH : 2 %Eu2+ remains 62.6 % of the initial intensity at 150 °C. Finally, the white light‐emitting diodes (WLED) fabricated by CBH : 2 %Eu2+, excited by a 365 nm chip, presents outstanding performances with a luminous efficacy (LE) of 13.9 lm/W, a color rendering index (CRI) of 89.4, and a correlated color temperature (CCT) of 5825 K. The above results show that CBH : Eu2+ can be used as a promising blue phosphor for WLED. This new method of low‐temperature self‐reduction can be applied to design and prepare other new types of highly efficient phosphors. Through a new method of low‐temperature (only 350 °C) self‐reduction, a highly efficient deep blue‐emitting phosphor Ca[B8O11(OH)4] : Eu2+ was prepared, with a high PLQY of 95 % and a color purity of 97.6 %. Then, a WLED fabricated by the as‐prepared CBH : 2 %Eu2+ presents outstanding performance with a luminous efficacy (LE) of 13.9 lm/W, a color rendering index (CRI) of 89.4, and a correlated color temperature (CCT) of 5825 K.