Investigation of upconversion phenomenon in Y1-xLn3+x(BTC)(DMF)2(H2O) and Y0.8-xYb0.2Ln3+x(BTC)(DMF)2(H2O) metal organic frameworks

Abstract

In this study, Y_1-xLn³⁺_x(BTC)(DMF)₂(H₂O) and Y_0.8-xYb_0.2Ln³⁺_x(BTC)(DMF)₂(H₂O) metal organic frameworks (MOFs), which structure included lanthanide ions, Ln³⁺ (Er³⁺, Ho³⁺, Tm³⁺, Yb³⁺, Nd³⁺), suitable for monitoring the upconversion phenomenon, have been synthesised. For this purpose the precursor of the organic moiety, benzene-1,3,5-tricarboxylic acid (BTC), as one of the simplest and very frequently cited carboxylic acid analogues in MOF syntheses, has been selected. By characterising upconversion properties of new MOFs it was determined that only Er³⁺ can be used as an activator for one centre luminescence upconversion by a ground state absorption/ excited-state absorption (GSA/ESA) mechanism, while with Yb³⁺, Ho³⁺, Tm³⁺ and Nd³⁺ ions the upconversion was not observed. It was also established that BTC cannot initiate triplet–triplet annihilation upconversion (TTA-UC) as this mechanism sensitizer. Yb³⁺–Er³⁺ and Yb³⁺–Ho³⁺ ion pairs as a sensitizeractivator were suitable for two-centre luminescence upconversion by a GSA/ excited-state upconversion (GSA/ESU) mechanism. A pair of Yb³⁺–Tm³⁺, contrary as shown in the literature review, does not exhibit upconversion properties in the synthesised MOFs.