Europium-Doped Calcium Silicate Nanoparticles as High-Quantum-Yield Red-Emitting Phosphors

Abstract

Europium ion-activated calcium silicate phosphors (Ca 2 SiO 4 :Eu 3+ ) with sharp red-light emission were fabricated via the hydrothermal method. The size of Ca 2 SiO 4 :Eu 3+ phosphors was controlled between 20 and 200 nm by precursor silicate particle sizes. Systematic studies to determine morphology, crystal phase, and photoluminescence (PL) were carried out for all the phosphors, and their optical efficiencies were compared. We found that the luminescence intensity and emission wavelength of Ca 2 SiO 4 :Eu 3+ phosphors depend on their particle sizes. Particularly, the Ca 2 SiO 4 :Eu 3+ synthesized with 20 nm silica seed contains the most intense red emission, high color purity, and high PL quantum yield. For the 20 nm-sized Ca 2 SiO 4 :Eu 3+ phosphor, PL quantum yields are measured to be above 87.95% and high color purity of 99.8%. The unusually high intensity of 5 D 0 → 7 F 4 emission (712 nm) is explained by structural distortion arising from silicate particle size reductions. We show that the obtained phosphor is a suitable candidate for solid-state lighting as a red component through CIE chromaticity coordinate and color purity measurements. Furthermore, the Ca 2 SiO 4 :Eu 3+ particles are examined for their validity as promising bio-imaging probes through cell labeling and imaging experiments and biodegradability studies.

Thermally Induced Morphological and Structural Transformations on Eu2+/Eu3+-Coactivated Calcium Silicate Nanophosphors

“…Conclusively, the Ca 2–0.05 SiO 4 : 0.05 Eu 3+ nanoparticles prepared with 20 nm silica showed significantly enhanced red emission (quantum efficiency: 87.95%, color purity: 99.8%) and a 400% increase in photoluminescence compared to the commercial silica one at 712 nm transition (Figure b). This enhanced optical performance is attributed to structural and spectroscopic alterations due to crystal size control …”

“…Specifically, under 270 nm excitation, the Ca 2–0.05 SiO 4 : 0.05 Eu 3+ sample with 20 nm silica showed a 35% increase in emission efficiency across the 575–725 nm spectrum compared to that of the sample with commercial silica. Under 397 nm excitation, the emission efficiency rose 130% in the same spectral range . These PLE and PL spectra results suggest that the Ca 2–0.05 SiO 4 : 0.05 Eu 3+ phosphor synthesized with 20 nm silica has superior UV absorption and effectively channels the excitation energy to the Eu 3+ ions, resulting in efficient PL emission.…”

“…Twenty nm silica nanoparticles (SNPs) were synthesized using the in situ silica sol–gel method, with some modifications based on previous studies. , The procedure began with thoroughly dispersing IGEPAL in cyclohexane through sonication for approximately 10 min and stirring at 30 °C for 30 min to ensure a uniform solution. Next, NH 4 OH and TEOS were added to the reaction mixture while vigorously stirring it overnight at 70 °C, resulting in the formation of spherical-shaped 20 nm SNPs.…”

“…In contrast, Eu 3+ ions emit in the orange-red or red spectral range, originating from their 5 D 0 - 7 F J ( J = 0–4) transitions. , Therefore, phosphors prepared by codoping Eu 2+ and Eu 3+ in a single host material can offer effective white light emission because they combine the blue-greenish emission of Eu 2+ with the red emission of Eu 3+ . − In our recent research, we successfully synthesized calcium silicate phosphors doped with trivalent europium ions (Eu 3+ ) (Ca 2 SiO 4 :Eu 3+ ), demonstrating exceptional luminescence properties, red emission, a high quantum yield (QY), and CCT. This was achieved through successful crystal size control in a hydrothermal synthesis using 20 nm silicate precursor seeds . In this study, we propose a thermal reduction process to enhance the material’s photoluminescent characteristics through coexistence of Eu 3+ and Eu 2+ in Ca 2 SiO 4 .…”

“…This was achieved through successful crystal size control in a hydrothermal synthesis using 20 nm silicate precursor seeds. 26 In this study, we propose a thermal reduction process to enhance the material’s photoluminescent characteristics through coexistence of Eu 3+ and Eu 2+ in Ca 2 SiO 4 . This tuning process had an impact on both the relative ratio of Eu 2+ -to-Eu 3+ ions and their crystal structure, adjusting the luminescence wavelengths of the phosphors ( Figure 1 ).…”