A broad spectrum photon responsive, paramagnetic β-NaGdF4:Yb3+,Er3+ – mesoporous anatase titania nanocomposite

Abstract

Herein, we report a novel single multifunctional platform based on broad-spectrum photoactive β-NaGdF₄:18% Yb³⁺, 2% Er³⁺ and mesoporous anatase TiO₂ for enhanced energy and simultaneous biomedical applications. Currently, the photoactive materials for solar energy harvesting applications have limitations in their efficiency due to their narrow photon absorption spectrum. The upconversion phosphor β-NaGdF₄:18% Yb³⁺, 2% Er³⁺ nanorods collect and harvest the NIR photons (∼980 nm) of sunlight and transform them into visible light via anti-Stokes emission (λ_em ∼521 and ∼540 nm), and the photoactive mesoporous anatase TiO₂ (mTiO₂) utilizes UV and weak visible photons, thus the composite forms a broad spectrum photon-capture system and improved power conversion efficiency for enhanced applications in photocatalysis, and dye sensitized solar cells (DSSCs). The photocatalytic activity of the nanocomposite showed an improvement in comparison to the mTiO₂ for the degradation of various dyes. In addition, the photocurrent density and solar cell efficiency of the nanocomposites showed an improvement by ∼24% and ∼17% respectively, over mTiO₂. The β-NaGdF₄:Yb³⁺,Er³⁺/mTiO₂ nanocomposite exhibits a strong paramagnetic signal (χ ∼ 6.45 × 10⁻⁵ emu g⁻¹ Oe⁻¹). The nuclear magnetic resonance (NMR) measurements showed large longitudinal T₁ relaxivity (r₁ = 7.09 s⁻¹ mM⁻¹) and magnetic resonance imaging showed enhanced T₁-weighted MRI images with increased concentrations of β-NaGdF₄:Yb³⁺,Er³⁺/mTiO₂ nanocomposite making them suitable for simultaneous magnetoresonance imaging. In addition, this composite system can also be used as a NIR triggered drug delivery system and in biomedical applications. Moreover, mesoporous TiO₂ is expected to increase the photocatalytic active sites, dye, and absorption, and drug loading capacity. The as-designed multifunctional β-NaGdF₄:Yb³⁺,Er³⁺/mTiO₂ nanocomposite possessed simultaneous multiple discrete functionalities with excellent luminescence properties, intrinsic paramagnetism, biocompatibility, improved photocatalytic activity, and solar cell efficiency. This work provides a promising system to utilize NIR light, which will contribute to efficient photon harvesting and biological applications.