Dual-emission luminescence thermometry using LaGaO3:Cr3+, Nd3+ phosphors

Abstract

A series of La_1−xGa_0.99O₃:Cr_0.01, Nd_x phosphors (where x = 0.005, 0.01, 0.02) for luminescence thermometry was synthesised by the solid-state method, structurally characterised using powder X-ray diffraction data, and investigated by ambient and variable-temperature optical measurements. The design principle relies on the use of a combination of transition metal and rare earth activator ions such that the excitation and emission wavelengths fall within the near infra-red spectral region, notably in the ‘first biological window’ that is attractive for potential in vivo applications. The photoluminescence spectra of the compounds feature the characteristic ²E phosphorescence of Cr³⁺ at 729 nm and the ⁴F_3/2 → ⁴I_9/2 emission of Nd³⁺ around 890 nm. The Nd³⁺ emission is quenched at a higher rate than that of Cr³⁺ with increasing temperature. Thermometric analysis by monitoring the luminescence intensity ratio (LIR) between the emissions of Cr³⁺ and Nd³⁺ from 300 K to 650 K shows a quasi-Boltzmann trend, with a maximum relative sensitivity of ∼2% K⁻¹, high absolute sensitivity values over this entire temperature range, excellent temperature resolution of 0.04 K at room temperature, and high stability.