Comparative optical thermometry analysis using Na2SrP2O7:Er3+/Yb3+ phosphors: evaluation of LIRTCL and LIRNTCL methods for high-resolution temperature sensing

Optical thermometry is a valuable non-contact technique for temperature measurement, especially in environments where traditional methods are impractical. Despite its advantages, enhancing the precision of optical thermometers remains a significant challenge. In this study, we explored the thermometric properties of Na2SrP2O7 phosphors co-doped with Er3+/Yb3+, synthesized via a solid-state reaction method, for temperature sensing within the 200-440 K range under 980 nm excitation. Upconversion (UC) luminescence, observed in the visible spectrum, was analyzed using the fluorescence intensity ratio (FIR) method, focusing on both thermally coupled (TCLs) and non-thermally coupled (NTCLs) energy levels of Er3+/Yb3+. Specifically, the transitions 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 were examined to calculate thermometric parameters. The maximum absolute sensitivity (S A) and relative sensitivity (S R) for the 2H11/2 → 4I15/2 to 4S3/2 → 4I15/2 transition were 0.0009 K-1 and 0.6% K-1, respectively, while for the 2H11/2 → 4I15/2 to 4F9/2 → 4I15/2 transition, S A was 0.004 K-1, with a maximum S R of 1.14% K-1. Furthermore, by employing a luminescence intensity ratio technique based on TCLs (LIRTCL), the minimum temperature uncertainty (δT) was found to be 1.31 K at 320 K. In contrast, the luminescence intensity ratio method based on NTCLs (LIRNTCL) yielded a much lower minimum δT value of 0.34 K at 200 K, indicating superior performance in terms of temperature resolution. These findings demonstrate that the LIRNTCL technique provides more sensitive and accurate temperature measurement compared to LIRTCL. The excellent temperature resolution and sensitivity of Na2SrP2O7:Er3+/Yb3+ phosphors highlight their potential for highly accurate optical thermometry applications in scientific and industrial contexts.

Color-tunable luminescence based on the efficient energy transfer of a Tm-Dy system for optical thermometry and white LED lighting

The development of phosphors with color-tunable luminescence including white emission is at the forefront of lighting and display technologies. Herein, Dy3+,Tm3+ single-doped or co-doped K3Y(PO4)2 phosphors are synthesized through the solid-state reaction method. By properly adjusting the ratio of Dy3+,Tm3+ co-doping concentrations, color-tunable luminescence from blue to yellow, including white luminescence, is realized under 359 nm excitation. The mechanism of energy transfer between Tm3+ and Dy3+ is further investigated via measuring the luminescence decay curve. Based on efficient energy transfer from Tm3+ to Dy3+, the emission of Dy3+ exhibits an abnormal thermal enhancement phenomenon as the temperature increases. The optical thermometry behaviors of various emission combinations for the Dy3+,Tm3+ co-doped system are analyzed. The maximum sensitivity can be obtained as a constant of 4.8 × 10-3 K-1, which is conducive to improve the measurement accuracy of optical temperature sensing at high temperatures. Furthermore, we also demonstrate the applicability of K3Y(PO4)2:Tm3+,Dy3+ phosphors in white LEDs, providing proof-of-concept for the lighting and display fields.

Promising lanthanide-doped BiVO4 phosphors for highly efficient upconversion luminescence and temperature sensing

The semiconductor oxide BiVO₄ has been intensively studied as a highly efficient photocatalyst. Here we attempt to adopt trivalent lanthanide (Ln³⁺)-doped BiVO₄ as a novel upconversion luminescence (UCL) material for achieving high-efficiency UCL and temperature sensing under near-infrared (NIR) irradiation. Er³⁺/Tm³⁺, Yb³⁺/Er³⁺, and Yb³⁺/Tm³⁺ ions were selected to co-dope the BiVO₄ phosphors, achieving three primary colors of red, green, and blue (RGB) with high color-purity. At an optimal doping concentration, the upconversion quantum yield of the BiVO₄:8%Yb³⁺,18%Er³⁺ phosphor reaches as high as 2.9%. Furthermore, we, for the first time, demonstrate the non-contact temperature sensing properties of a BiVO₄:Er³⁺,Tm³⁺ phosphor via employing fluorescence intensity ratio technology. The results show that the maximum absolute thermal sensitivity is ≈70 × 10^-4 K^-1 at 473 K under 980 nm excitation, with high and stable sensitivity of more than 60 × 10^-4 K^-1 over a wide temperature range of 333-493 K. In addition, at a much safer wavelength of 1550 nm, this sample achieves maximum absolute sensitivity of 56 × 10^-4 K^-1 at 453 K. Moreover, the BiVO₄:Er³⁺,Tm³⁺ phosphor presents high relative sensitivity of about 1.1% K^-1 under both 980 and 1550 nm excitation at 293 K. These results indicate that the BiVO₄ semiconductor oxide can be used as a novel host to achieve high UCL efficiency and promising thermal sensing performance, suggesting potential applications in the new fields of anti-counterfeiting, displays, and non-contact temperature sensors.

Managing optical heating via Al3+-doping in Er3+:SrF2 powder phosphors prepared by combustion synthesis

Quenching of photoluminescence due to optical heating generated by high power laser sources has been identified as a major concern for photonics applications that relies on inorganic phosphor materials. Here we investigate how erbium-doped strontium fluoride (Er3+:SrF2) powders prepared by combustion synthesis respond to intense optical heating. We found that the near-infrared to visible photon up-conversion (UC) luminescence from Er3+ was quenched and the internal temperature of the sample increased from 298 to 695 K when the excitation power of a CW diode laser operating at 808 nm was increased from 0.1 to 2.1 W. However, when SrF2 was co-doped with Al3+, we observed an increase in the UC intensity and an unexpected internal temperature reduction of up to 155 K for an excitation power of 2.1 W. Our analysis suggests that Al3+ decreases the phonon energy and increases the local symmetry of the environment of the rare-earth ion in SrF2.

Enhancement of 1.5 μm fluorescence signal from Er3+ due to Yb3+ in yttrium silicate powders pumped at 975 and 808 nm

The effect of the presence of ytterbium (Yb³⁺) on the near-infrared (NIR) emission profile of erbium (Er³⁺), more specifically the ⁴I_13/2 → ⁴I_15/2 radiative transition around 1.5 μm, in yttrium silicate crystalline ceramic powders prepared by combustion synthesis was investigated under different NIR laser excitation wavelengths (λ = 808 and 975 nm). Enhancement of fluorescence around 1.5 μm due to the presence of Yb³⁺ was observed, which has potential use in medicine (NIR-III biological window) and optical communications (C-band transmission window). Two different excitation channels involving energy transfer between Er³⁺ and Yb³⁺ were studied: one involving the sensitization of Er³⁺ by Yb³⁺ (for λ = 975 nm laser light excitation) and the other involving direct excitation of Er³⁺ with Yb³⁺ acting as an energy reservoir (for λ = 808 nm laser light excitation). The energy transfer mechanisms of both processes are discussed in the text.

Effects of Tm3+ concentration on upconversion luminescence and temperature-sensing behavior in Tm3+/Yb3+:Y2O3 nanocrystals

The effects of Tm³⁺ concentration on upconversion emission and temperature-sensing behavior of Tm³⁺/Yb³⁺:Y₂O₃ nanocrystals were investigated. Blue and red emissions were observed under 980 nm excitation. Both upconversion emissions and the blue to red intensity ratio were found to decrease with increasing Tm³⁺ concentration. The temperature-sensing performances of the samples were studied, the fluorescence intensity ratio of ¹G_4(a)→³H₆ (477 nm) and ¹G_4(b)→³H₆ (490 nm) transitions from Tm³⁺ ions was chosen as the thermometric index. The results showed that the sensor sensitivity was sensitive to Tm³⁺ ion concentration. The maximum sensitivity of ~32 × 10^-4 K^-1 was obtained for 0.1%Tm³⁺/5%Yb³⁺:Y₂O₃ nanocrystals at 344 K. Moreover, a marked optical induced heating effect was also found in the nanocrystals. The prepared Tm³⁺/Yb³⁺:Y₂O₃ nanocrystals could be used in temperature-sensing probes and in optical heaters.

Solution Combustion Synthesis of Nanoscale Materials

Solution combustion is an exciting phenomenon, which involves propagation of self-sustained exothermic reactions along an aqueous or sol-gel media. This process allows for the synthesis of a variety of nanoscale materials, including oxides, metals, alloys, and sulfides. This Review focuses on the analysis of new approaches and results in the field of solution combustion synthesis (SCS) obtained during recent years. Thermodynamics and kinetics of reactive solutions used in different chemical routes are considered, and the role of process parameters is discussed, emphasizing the chemical mechanisms that are responsible for rapid self-sustained combustion reactions. The basic principles for controlling the composition, structure, and nanostructure of SCS products, and routes to regulate the size and morphology of the nanoscale materials are also reviewed. Recently developed systems that lead to the formation of novel materials and unique structures (e.g., thin films and two-dimensional crystals) with unusual properties are outlined. To demonstrate the versatility of the approach, several application categories of SCS produced materials, such as for energy conversion and storage, optical devices, catalysts, and various important nanoceramics (e.g., bio-, electro-, magnetic), are discussed.

Photon conversion in lanthanide-doped powder phosphors: concepts and applications

Structural and optical properties of a lanthanide-doped material (Er³⁺, Yb³⁺ co-doped Y₂SiO₅ powder) prepared by combustion synthesis.

Investigation into the temperature sensing behavior of Yb3+ sensitized Er3+ doped Y2O3, YAG and LaAlO3 phosphors

The sensitivities (S) of Y₂O₃ (YAG/LaAlO₃):Yb³⁺/Er³⁺ phosphors increased with increasing average bond covalency and the calculated values were basically in good agreement with our experimental results.