Three-photon upconversion and optical thermometry characterization of Er3+:Yb3+ co-doped yttrium silicate powders

The effect of the presence of ytterbium (Yb3+) on the upconversion (UC) emission of erbium (Er3+) in yttrium silicate crystalline ceramic powders prepared by combustion synthesis was investigated under continuous wave (cw) near-infrared (λ = 975 nm) laser excitation. UC emission bands centered at ∼380, ∼410, ∼480, ∼530, ∼555 and ∼660 nm were identified, respectively, as 4f–4f transitions from Er3+ excited states 4G11/2, 2H9/2, 4F7/2, 2H11/2, 4S3/2 and 4F9/2. Aiming to photonics applications, the optical temperature sensor performance of this material was also investigated by measurements of the fluorescence intensity ratio of the signals at 530 and 555 nm in the temperature range of 300–600 K. The maximum sensor sensitivity found was ∼56 × 10−4 K−1. We observed that the maximum sensor sensitivity increased to ∼70 × 10−4 K−1 when the cw laser excitation was replaced by a pulsed (∼5 ns) laser excitation. The change in sensor sensitivity is attributed to optical heating of the sample that occurs under cw excitation.