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Despite the numerous advantages of lanthanide based luminescent thermometers, a major limitation is the limited brightness associated with the low absorption cross section of the 4f–4f transitions. In this paper, co-doping with Cr3+/4+ is proposed as a strategy to enhance the near-infrared luminescence emission of Nd3+/Er3+-based luminescent thermometers, as well as to modulate the temperature sensitivity of the ratio of Nd3+ to Er3+ in YAG microcrystals. It was found that an increase in the Cr3+ concentration leads to the enhancement of the YAG:Nd3+,Er3+ emission intensity via the Cr3+ → Ln3+ sensitization process. The quantitative analysis of the absolute brightness indicates the 30-fold enhancement of their near infrared emission upon broad white light excitation for 20% Cr3+ with respect to the non co-doped with the Cr3+ counterpart. In addition, the phonon-assisted nature of the simultaneously occurring Cr3+ → Ln3+ and Nd3+ → Cr4+ → Er3+ energy transfers leads to a 7-fold increase of the relative temperature sensitivity of the ratio of Nd3+ to Er3+ emission. In conclusion, co-doping with transition metals can enhance simultaneously the luminescence brightness and the temperature sensitivity of NIR luminescent thermometers, holding promise for sensitive and robust remote temperature sensing at physiological temperatures. [ABSTRACT FROM AUTHOR]

We report on the synthesis, photoluminescence optimization and thermometric properties of Sr 3 Al 2 O 5 Cl 2 :Eu 2+ and SrAl 2 O 4 :Eu 2+ phosphor powders. The photoluminescence of Sr 2.9 Al 2 O 5 Cl 2 :0.1Eu 2+ phosphors exhibits a blue-shift with an increasing annealing temperature owing to a decrease in the crystal field strength of the host caused by evaporation of Cl from the material. The quenching of the blue band in favour of the red band observed in the luminescence spectra of Sr 2.9 Al 2 O 5 Cl 2 :0.1Eu 2+ with an increased annealing temperature was explained using the mechanism of the Landau-Zener transitions. The quantum yield and the lifetime of the phosphors depend on the annealing temperature. Phosphor samples annealed at 850 °C, 1000 °C, 1200 °C and 1500 °C were found to be potential luminescence thermometers using the luminescence spectral method. For Sr 3 Al 2 O 5 Cl 2 :Eu 2+ annealed at 1000 °C, the temperature-dependent dual-band intensity ratio demonstrated a high-temperature sensitivity of ∼1.47%/°C in the temperature range of 23 °C to 40 °C which is superior to other reported phosphors with a microsecond decay time, suggesting that the material has potential for sensitive thermometry applications at ambient temperatures.