The influence of Nd3+ concentration and alkali ions on the sensitivity of non-contact temperature measurements in ALaP4O12:Nd3+ (A = Li, K, Na, Rb) nanocrystalline luminescent thermometers

Abstract

Luminescent properties of ALaP₄O₁₂:Nd (A = Li, Na, K, Rb) nanocrystals were measured as a function of temperature. It was found that three spectroscopic parameters were temperature dependent, namely: the position of the emission band (λ_M), its full width at half maximum (FWHM) and the luminescence intensity ratio (LIR) between the R₁ → Z₁ and R₂ → Z₁ Stark components. The influence of the dopant concentration and the type of tetraphosphate host on the sensitivity of luminescent thermometers was analyzed. It was found that the sensitivity of Nd³⁺ based luminescent thermometers (LIR) decreases with increasing dopant concentration.The band position was found to have the highest temperature sensitivity, while the lowest was that of the luminescence intensity ratio figure of merit. The highest sensitivity of LIR based thermometers was found for LiLaP₄O₁₂:1%Nd nanocrystals, reaching 0.31% K⁻¹. The influence of dopant concentration on the sensitivity of luminescent thermometers was discussed in terms of different electron–phonon interaction strengths.