Eu²⁺ Site Preferences in the Mixed Cation K₂BaCa(PO₄)₂ and Thermally Stable Luminescence

Site preferences of dopant Eu²⁺ on the locations of K⁺, Ba²⁺, and Ca²⁺ in the mixed cation phosphate K₂BaCa­(PO₄)₂ (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu²⁺ ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu²⁺ phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu²⁺ 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs

Eu²⁺ Site Preferences in the Mixed Cation K₂BaCa(PO₄)₂ and Thermally Stable Luminescence

Site preferences of dopant Eu²⁺ on the locations of K⁺, Ba²⁺, and Ca²⁺ in the mixed cation phosphate K₂BaCa­(PO₄)₂ (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu²⁺ ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu²⁺ phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu²⁺ 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs

Site Occupation Engineering toward Giant Red-Shifted Photoluminescence in (Ba,Sr)₂LaGaO₅:Eu²⁺ Phosphors

Exploring oxide-based red-emitting phosphors is essential for improving the color rendering index (Ra) and reducing the correlated color temperature (CCT) of white-light-emitting diode (LED) lighting sources. Especially, it is challenging to design Eu2+ red emission in inorganic solids. Here, the Eu2+-activated oxide phosphor Sr2LaGaO5:Eu2+ was synthesized with red emission peaking at 618 nm under 450 nm excitation. The crystal structure and spectral analysis indicate that Eu2+ tends to occupy [Sr1/LaO8] polyhedrons with a smaller coordination number, resulting in a large crystal field splitting at the 5d level and realizing the broadband 4f–5d red emission. When Sr is substituted by Ba atoms, density functional theory calculations verify that Ba tends to enter [Sr2O10] with a large coordination number, further giving rise to the lattice distortion and a giant spectral redshift (618–800 nm). The white LED device fabricated by mixing red Sr1.8Ba0.2GaO5:Eu2+ and green Lu3Al5O12:Ce3+ phosphors exhibits a high color rendering index (Ra = 92.1) and a low color-dependent temperature (CCT = 4570 K). This study will give guidance for exploring new Eu2+ activated oxide-based red phosphors as well as achieving tunable emission through cations’ substitution