Solid-state inorganic phosphors for luminescence thermometry

Abstract

Through the link between emission quenching and temperature, luminescence thermometry has emerged as a remote, semi-contact method for temperature sensing. This thesis investigates through variables including the host material choice, and the luminescent ion’s identity and concentration, how solid-state thermometers can be designed for specific purposes such as for biological use, with high sensitivity and temperature resolution.

Chapter 1 reviews phosphor constituents, theory of luminescence, method of luminescence thermometry, and current luminescence thermometers using different host materials.
Chapter 2 gives an overview on all methods used in the synthesis and characterisation of the host material’s structure, and the optical properties of the introduced activator ions.
Chapter 3 investigates the LaGa1-xO3:Cr3+x phosphor series (x = 0.0, 0.2, 0.5, 1.0, 2.0, 4.0 mol%). Room-temperature luminescence measurement showed LaGa0.99O3:Cr0.01 with the highest quantum yield of the series. Investigation of LaGa0.99O3:Cr0.01 by variable-temperature photoluminescence confirmed its application as a luminescence thermometer with a relative sensitivity of 2.5% K-1 and a temperature resolution of 0.04 K at 300 K.
Chapter 4 explores the La1-xGa0.99O3:Cr3+0.01, Nd3+x series (where x = 0.5, 1.0, 2.0 mol%). Emission from both Cr3+ and Nd3+ using a single excitation wavelength was confirmed. Variable-temperature emission of the materials presented La0.98Ga0.99O3:Cr3+0.01, Nd3+0.02 as the best candidate for luminescence thermometry, with a relative sensitivity of 2.0% K-1 and a temperature resolution of 0.05 K at 300 K.
Chapter 5 discusses the A5(V0.97O4)3Cl: Mn5+0.03 materials (where A = Sr2+, Ba2+). Room-temperature luminescence investigations confirmed Mn5+ emission within biological window-2 with quantum yields recorded as 47% and 51% respectively. Variable-temperature investigation confirmed both materials as luminescence intensity ratio (LIR), band-shift, and bandwidth thermometers. Multiparametric linear regression (MLR) thermometry of Sr5(V0.97O4)3Cl: Mn5+0.03 gave a relative sensitivity of 3.14% K-1 and a temperature resolution of 0.042 K at 308 K.
Chapter 6 concludes with the closing remarks on all discussed work, alongside a perspective on further work that can be continued on the presented, and similar, materials.