Temperature sensitivity modulation through crystal field engineering in Ga3+ co-doped Gd3Al5-xGaxO12:Cr3+, Nd3+ nanothermometers

Luminescent nanothermometry (LNT) based on temperature-dependent emission intensity of transition metals (TM) is a promising new direction to enhance the performance and implement LNT in many fields of science and technology. However, insightfully understanding and analysis of the luminescence thermal quenching mechanisms in this type of compounds is required. In this work, we study temperature sensitivity (S) modified by crystal field engineering in Gd₃Al_5-xGa_xO₁₂:Cr³⁺, Nd³⁺ TM:LNTs. Substituting Al³⁺ ions in the host matrix by Ga³⁺ ones, caused gradual decline of crystal field strength from Dq/B = 2.69 for Gd₃Al₅O₁₂:Cr³⁺, Nd³⁺ to the Dq/B = 2.18 for Gd₃Ga₅O₁₂:Cr³⁺, Nd³⁺. In consequence, improvement of relative sensitivity was observed. Two temperature dependent parameters were taken into considerations as potential temperature measure, i.e. luminescence intensity ratios of ⁴T₂ → ⁴A₂ (Cr³⁺) to ⁴F_3/2 → ⁴I_9/2 (Nd³⁺) and ²E → ⁴A₂ (Cr³⁺) to ⁴T₂ → ⁴A₂ (Cr³⁺). The proposed method, based on crystal field strength engineering, improved the relative temperature sensitivity by over 1.37%/°C for −1 Dq/B change in crystal field strength, from initial 1.2–1.9%/°C.

… Instruments. Temperature dependent emission spectra were measured using 450nm excitation line from laser diode and recorded using a Silver-Nova Super Range TEC Spectrometer form Stellarnet of 1 nm spectral resolution …