Host sensitized intense infrared emissions from Ln3+ doped GdVO4 nanocrystals: ranging from 950 nm to 2000 nm

Abstract

In this communication we report the observation of intense near infrared (NIR) emissions in the 900 nm to 2000 nm range from colloidal water dispersible lanthanide (Ln³⁺) doped GdVO₄ nanocrystals (Ln = Sm³⁺, Nd³⁺, Dy³⁺, Tm³⁺, Er³⁺ and Ho³⁺). Observing strong NIR emission, particularly from aqueous medium, is a challenge as the luminescence is more prone to non-radiative relaxation. The observed intense NIR emissions from Ln³⁺-doped GdVO₄ nanocrystal ions are attributed to the efficient sensitization of the Ln³⁺ excited levels via a GdVO₄ host matrix. The GdVO₄ matrix shows intense and broad absorbance in the ultraviolet (UV) region resulting from the charge transfer from the 2p orbital of oxygen to the d orbital of V⁵⁺ ions of the VO₄⁻ group. Upon UV excitation, GdVO₄ absorbs the light and efficiently transfers the energy to the excited state of the Ln³⁺ ions, which emit in the NIR region. The calculated energy transfer efficiencies for most of the studied Ln³⁺ ions are about 90%. In fact, the observed enhancement in the NIR emission intensity varies between 3 (for Sm³⁺) and 53 fold (Nd³⁺) compared to direct excitation. The combination of high aqueous stability and intense NIR emission can be advantageous for applications like NIR bioimaging. In addition, these colloidal nanocrystals can easily be incorporated into sol–gel or glass matrices for the fabrication of devices such as optical amplifiers, fiber optics for telecommunications, etc.