Revisiting Cr³⁺-Doped Bi₂Ga₄O₉ Spectroscopy: Crystal Field Effect and Optical Thermometric Behavior of Near-Infrared-Emitting Singly-Activated Phosphors

Abstract

The increasing interest in the development of ratiometric optical thermal sensors has led to a wide variety of new systems with promising properties. Among them, singly-doped ratiometric thermometers were recently demonstrated to be particularly reliable. With the aim to discuss the development of an ideal optical thermal sensor, a combined experimental and theoretical insight into the spectroscopy of the Bi2Ga4O9:Cr3+ system is reported showing the importance of an insightful analysis in a wide temperature range. Low-temperature photoluminescence analysis (from 10 K) and the temperature dependence of the lifetime investigation, together with the crystal field analysis and the modeling of the thermal quenching process, allow the estimation of key parameters such as the Debye temperature (cutoff frequency), the Huang–Rhys parameter, and the energy barrier between 2Eg and 4T2g. Additionally, by considering the reliable class of singly-doped ratiometric thermometers based on a couple of excited states obeying the Boltzmann law, the important role played by the absolute sensitivity was discussed and the great potential of Cr3+ singly-activated systems was demonstrated. The results may provide new guidelines for the design of reliable optical thermometers with outstanding and robust performances.

Boltzmann Thermometry in Cr3+‐Doped Ga2O3 Polymorphs: The Structure Matters!

“…The values calculated at 300 K are 0.64% and 1.05% K −1 for β‐Ga 2 O 3 :Cr 3+ and α‐Ga 2 O 3 :Cr 3+ , respectively. The absolute sensitivity is also an important parameter giving information on the extent of change of the thermometric parameter with the temperature [ 23 ] and, consequently, the ability to discriminate small variation of temperatures as can be inferred by considering the relationship between the temperature uncertainty δT (also defined as thermal resolution Δ T ) and S a where δLIR is the uncertainty on the calculation of the LIR. Despite the difficulty to compare the S a values due to the different setup employed by different groups, it is worth mentioning that the values are calculated to be in the order of 10 −2 for both the thermometers in the whole temperature range (Figure 5b) suggesting promising ability to discriminate small variation of temperature.…”

Cr3+‐Doped Broadband NIR Garnet Phosphor with Enhanced Luminescence and its Application in NIR Spectroscopy

“…Luminescence of Cr 3+ is originated from transition between outer 3d levels, which is sensitive to both crystal field and electron–phonon coupling . To modify the local crystal field of Cr 3+ , ion substitution was widely adopted . In recent years, a strategy named “chemical unit co‐substitution” was developed from complex polyatomic substitution, which changes two structural units at the same time.…”

Efficient Super Broadband NIR Ca2LuZr2Al3O12:Cr3+,Yb3+ Garnet Phosphor for pc‐LED Light Source toward NIR Spectroscopy Applications

“…In recent years, many researches have been focused on the development of the broadband NIR phosphors . OSRAM has demonstrated the prospect of NIR phosphors for endoscopy applications that facilitates mobile phones for analyzing the food composition .…”