Down-conversion luminescence and temperature sensing characteristics of LaSrGaO₄ :Er³

Erbium(III) ion (Er³⁺ ) has abundant energy levels that can emit light covering a quite broad wavelength range in many hosts. Here we synthesized LaSrGaO₄ :Er³⁺ phosphors by a high-temperature solid-state method. Upon excitation at the ultraviolet (UV) band, LaSrGaO₄ :Er³⁺ phosphors could emit green, red and near-infrared emission simultaneously. The temperature dependent emission characteristics of the as-prepared samples was then studied and two kinds of luminescent ratiometric thermometry were constructed. The first one is on the basis of two green emission bands that stems from the ² H_11/2  → ⁴ I_15/2 and ⁴ S_3/2  → ⁴ I_15/2 transitions of Er³⁺ . The intensity ratio between these two emission bands was found to follow well with the Boltzmann distribution, and its maximum relative sensitivity was calculated to be 0.84% K^-1 at 299 K. The other one depends on the ⁴ F_9/2  → ⁴ I_15/2 transition of Er³⁺ and self-luminescence of the host LaSrGaO₄ , considering that these two emission lines have different temperature response. The relative sensitivity of this type of luminescence intensity ratio (LIR) thermometry could reach 1.86% K^-1 at 299 K, we have successfully developed materials with one of the largest relative sensitivities to date, which provides some basis for the subsequent development of a new type of non-contact temperature sensor.