Upconversion and Optical Nanothermometry in LaGdO₃: Er³⁺ Nanocrystals in the RT to 900 K Range

Abstract

The search for material hosts being able to incorporate Er 3+ impurities with a thermally stable structure and a high melting temperature is priority in optical thermometry. In this work, we report on the structural and spectroscopic characterization of Er 3+ -doped and Yb 3+ /Er 3+codoped LaGdO 3 nanocrystals synthesized via the sol−gel Pechini method. X-ray diffraction and Raman spectroscopy unequivocally show that the synthesis method provides nanocrystals with a single-phase B-type monoclinic structure (space group, C2/m). Intensity decay curves, I(t), were measured to investigate the efficiency of upconversion processes yielding green emission. We showed that an energy transfer upconversion (ETU) process involving Yb−Er pairs governs visible emission upon near-infrared (NIR) excitation. The temperature dependence of the thermalized green luminescence at 525 nm ( 2 H 11/2 → 4 I 15/2 ) and 549 nm ( 4 S 3/2 → 4 I 15/2 ) was checked for thermometric applications in the room temperature (RT) to 900 K range. We demonstrate that the B-type monoclinic phase of LaGdO 3 is stable from low temperatures up to 900 K. Doped with Er 3+ , it shows suitable thermometer capabilities with a maximum sensitivity of S = 4.3 × 10 −3 K −1 at 554 K and a relative sensitivity decreasing from its maximum value at 0 K to S R = 1.2 × 10 −2 K −1 at 298 K. The results suggest that LaGdO 3 in its B-type monoclinic phase is a promising material as a wide-range temperature sensor, without any further surface protection.

Thermal Analysis of High Entropy Rare Earth Oxides

“…They all show an orthorhombic ( Pnma ) distortion and do not melt congruently, but decompose at 800–2000 °C into solid solutions of one of rear earth oxide structure types [ 39 ]. LaGdO 3 in a B-type structure attracted attention for application as high-k gate dielectric [ 40 ] and as an optical temperature sensor when doped with Er/Yb [ 41 , 42 ].…”

Upconversion luminescence and temperature sensing properties of Yb2(MoO4)3:Ln3+ (Ln = Ho, Tm, Er) phosphors based on energy transfer

“…For an optical temperature sensor, sensitivity is an important criterion to measure whether it is practical. Sensitivity is divided into absolute sensitivity and relative sensitivity, which are expressed by formula (8) and (9) respectively: 59 …”

Ultrasensitive optical thermometer based on abnormal thermal quenching Stark transitions operating beyond 1500 nm

“…Non-invasive optical thermometry based on fluorescence intensity ratio (FIR) of thermally coupled energy levels (TCLs) of lanthanide ions in upconversion (UC) materials is a promising way to get over the above technical obstacle, due to the features of outstanding anti-jamming ability, excellent accuracy, and quick response capacity. [7][8][9][10] Meanwhile, UC materials own the advantages of high photostability and low toxicity, which makes them the promising candidates for monitoring the temperature in vivo. [11][12][13][14][15][16] However, the clinical performance of UC thermometers is far from satisfactory, which is severely hindered by the shallow penetration depth of the emitting visible light inside the organism resulting from the strong absorption and scattering by bio-tissues.…”