Upconversion Luminescence Properties Research Articles

Untypical tuneable emission activated by NIR radiation observed in gadolinium borate nanomaterials doped with Yb3+, Ho3+ and Ce3+ ions

New luminescent nanoparticles with adjustable emission properties were synthesized via a hydrothermal method to investigate the effect of Ce3+ concentration on the tuneable emission properties of Yb3+/Ho3+ co-doped gadolinium borates. The synthesized samples’ comprehensive structural and morphological analysis was conducted utilizing X-ray diffraction and transmission electron microscopy. To obtain highly crystalline nanoparticles GdBO3:Yb3+/Ho3+/Ce3+ characterized by intense and bright emission, they were annealed at 525 °C and 925 °C. Under the excitation of 972 nm, the tunable yellow to green up-conversion (UC) emission was observed, while the Ce3+ concentration increased. This change correlated with a difference in the correlated color temperature from 4345 K to 5442 K, respectively. The untypical changes observed in the red-to-green (R/G) ratio, displaying a declining trend contrary to conventional expectations, allowed for the proposed mechanism for understanding their UC luminescence properties. The results obtained indicate that the Ce3+ doped GdBO3:Yb3+/Ho3+ nanoparticles demonstrate high application potential for anti-counterfeiting.

Innovative synthesis of Tm³⁺/Er³⁺-doped Yb-YGG single crystals for upconversion-based white light emission

In recent years, there has been a growing interest in developing advanced materials for photonics applications, particularly for efficient white light emission, which is crucial for technologies like solid-state lighting and display devices. One interesting approach for emitting white light is Upconversion (UC) luminescence. This study focuses on synthesis, by a new and alternative method, and characterization of yttrium ytterbium gallium garnet (Yb-YGG) single crystals, specifically Y1.8Yb1.2Ga5O12, doped with various concentrations of Er3+ and Tm3+ ions. These crystals were studied intending to enhance UC luminescence properties for white light generation by modifying their respective emissions in the red, green, and blue (RGB) regions. Unlike traditional methods such as Czochralski, these crystals were produced by controlled nucleation and growth through gradual cooling of a specific glass mixture, leading to Yb-YGG single crystals doped with different concentrations of Yb3+, Er3+, and Tm3+ ions. By optimizing the Yb3+/Tm3+/Er3+ ratio, the study allowed to obtain micrometric single crystals that efficiently emit white light via UC. The crystals were characterized by X-ray diffraction, optical and electronic microscopies, EDS and luminescence spectroscopy.

Improved upconversion luminescence of NaBiF4: Tm3+/Yb3+/Al3+ as a ratio thermometer

NaBiF4: 0.5 %Tm3+/20 %Yb3+/x%Al3+ upconversion luminescence materials were synthesized by co-precipitation method. The crystal structure, upconversion luminescence properties and temperature measurement properties systematically studied. Under 980 nm laser excitation, the characteristic transitions of Tm3+ were observed, corresponding to 1G4 → 3H6 (475 nm), 1G4 → 3F4 (650 nm), 3F2, 3 → 3H6 (700 nm) and 3H4 → 3H6 (800 nm), respectively. Al3+ substitution significantly increases the upconversion luminescence intensity, and the fluorescence lifetime of 1G4 level shortens from 277.8 to 179.1 μs. An anomalous thermal enhancement behavior is observed. The optical thermometry properties of Tm3+ based on the non-thermally coupled energy levels 3F2, 3 and 3H4 have been studied using the fluorescence intensity ratio technique. Relative sensitivity and absolute sensitivity show maximum values at 316 K, which are 1.1 % K−1 and 0.21 % K−1, respectively. The above results demonstrate that this material is a promising optical ratio thermometer.

Synthesis and characterizations of upconverting luminescent Er3+/ Yb3+: Gd2O3 uniform nanospheres for biomedical applications

We present the synthesis of Er3+/ Yb3+ co-doped Gd2O3 nanospheres using the wet-chemical method followed by a synergistic step-by-step calcination process, a novel approach in the field. The nanospheres exhibited red color upconversion luminescence (UCL) after multi-step annealing at temperatures ranging from 650 °C to 1150 °C, achieving a fully spherical morphology. The diameter and surface morphology of the nanospheres were significantly altered by the annealing process, decreasing from 382.77 ± 1.72 nm with a smooth surface to 245.7 ± 1.31 nm with a rougher surface. The UCL intensity increased with the annealing temperature. The influence of Er3+/ Yb3+ co-doped Gd2O3 nanospheres, excited by a 975 nm laser, was investigated, and the decay time for UCL samples was analyzed. The luminescence peak at 1026 nm was attributed to the 4I11/2 (Er3+) + 2F7/2 (Yb3+) → 4I15/2 (Er3+) + 2F5/2 (Yb3+) transition/ or 2F5/2 → 2F7/2 of the Yb3+ ions within the Gd2O3 matrix. Furthermore, the UCL properties of Er3+/ Yb3+ co-doped Gd2O3 nanophosphors were explored to detect the NTERA-2 cancer cells. These findings suggest that the rare earth co-doped Gd2O3 nanospheres might hold significant potential for biomedicine and imaging diagnostics applications, sparking new interest and possibilities in these fields.

Enhancing upconversion luminescence intensity of BiTa7O19:Er3+/Yb3+/Mo4+ by doping Sc3+ or Sb

AbstractBased on the previous optimal concentration of Er3+/Yb3+/Mo4+ co‐doped BiTa7O19 (BTO) samples, Sc3+ or Sb is planned to be doped into BTO:Er3+/Yb3+/Mo4+ for further improving the upconversion luminescence (UCL) intensity under 980‐nm laser excitation. A series of BTO:Er3+/Yb3+/Mo4+/Sc3+ and BTO:Er3+/Yb3+/Mo4+/Sb samples are prepared by high‐temperature solid‐phase sintering method. The microstructure and UCL properties are investigated by X‐ray diffraction, Raman, X‐ray photoelectron spectroscopy (XPS), diffuse reflection, and luminescence spectrum. The green UCL intensity of BTO:Er3+/Yb3+/Mo4+/Sb is little better than that of BTO:Er3+/Yb3+/Mo4+/Sc3+, which reaches 2.40 times than that of β‐NaYF4:Er3+/Yb3+. XPS results show that Sc is 3+, Mo is 4+, and Sb is 3+ and 5+. Raman spectra show that BTO:Er3+/Yb3+/Mo4+/Sb has lower phonon energy and more disorder than BTO:Er3+/Yb3+/Mo4+/Sc3+. The maximum relative temperature sensitivity is got as 0.01012 K−1 at 303 K based on luminescence intensity ratio technology. BTO:Er3+/Yb3+/Mo4+/Sb has outstanding pure green UCL intensity, which can be applied to luminescence display and temperature sensing.

Preparation and significant enhancement of upconversion luminescence of α-Ba2ScAlO5:Yb3+/Er3+ phosphors by Ca2+ ions doping

The intensity of upconversion luminescence (UCL) poses a significant challenge for oxides characterized by high phonon energy. Herein, a significant enhancement of red UCL is achieved through the introduction of an intermediate band (IB) in α-Ba2ScAlO5: Yb3+/Er3+ by Ca2+ ions doping. The absorption spectra verify the existence of the IB. The IB of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+ increases the host's absorption of excited photons, provides more electrons for the excitation of Er3+, and realizes the enhancement of UCL emission. The optimal concentration of Ca2+ in α-Ba2ScAlO5: 0.2Yb3+, 0.03Er3+ is 0.15. Compared with undoped Ca2+ samples, the red and green UCL intensity of α-Ba2ScAlO5: Yb3+, Er3+, 0.15Ca2+ increased by 48.2 and 10.6 times, respectively. The mechanism of Ca2+ enhanced UCL was investigated by analyzing the UCL spectra, absorption spectra and lifetime decay curves of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+. The temperature-dependent UCL properties of α-Ba2ScAlO5: Yb3+/Er3+/Ca2+ were also studied by the 2H11/2 (525 nm) and 4F9/2 (667 nm) energy level radiation transitions. The observed linear correlation between luminescence intensity and temperature, coupled with its high sensitivity, indicates the promising potential for temperature sensing applications. This study not only opens a new avenue for enhancing UCL but also holds significant implications for sparking widespread interest in non-contact temperature sensing applications leveraging UCL.

Synthesis and Upconversion Luminescence Fine-tuning of Yb3+/Ho3+-Doped Indium and Gallium Oxide Nanoparticles.

Rare earth (RE) dopants can modulate the bandgap of oxides of indium and gallium and provide extra upconversion luminescence (UCL) abilities. However, relevant UCL fine-tuning strategies and energy mechanisms have been less studied. In this research, InGaO, Ho3+ monodoped and Yb3+/Ho3+ codoped In2O3, and Ho3+ monodoped Yb3Ga5O12 nanoparticles (NPs) were synthesized by a solvothermal method. The effects of Yb3+ and Ho3+ dopants on the crystal structures, UCL properties, and optical bandgaps of the oxides were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UCL spectroscopy, and measurements of decay times, pump power dependence, and transmittance spectra. The crystal structures of oxide products of indium and gallium were significantly modified with RE dopants. In2O3 and Yb3Ga5O12 were selected as the host materials. For Yb3+/Ho3+ codoped In2O3 NPs, there existed energy transfers from the defect states of In2O3 to Ho3+ and from Yb3+ to Ho3+. With a fixed Ho3+ concentration, In2O3:0%Yb3+,2%Ho3+ NPs showed the optimal UCL properties mainly due to In2O3-Ho3+ energy transfer and Ho3+-Yb3+ energy-back-transfer, while with a fixed Yb3+ concentration, In2O3:5%Yb3+,3%Ho3+ NPs with a slight Yb2O3 impurity and Yb3Ga5O12:2%Ho3+ NPs did mainly due to Ho3+-Ho3+ cross-relaxation. Besides, the optical bandgaps of In2O3 and Yb3Ga5O12 were noticeably broadened with RE dopants. These findings can offer feasible directions for the synthesis and UCL fine-tuning of RE-doped oxides of indium and gallium and improve their multifunction application prospects in the fields of semiconductor and UCL nanomaterials.

Up-Conversion Luminescence and Optical Temperature-Sensing Properties of Yb3+ and Er3+ Co-doped Yttrium Aluminum Garnet Phosphor

Up-Conversion Luminescence and Optical Temperature-Sensing Properties of Yb3+ and Er3+ Co-doped Yttrium Aluminum Garnet Phosphor

Sr2BiF7: A New Bismuth-Based Host Material for Lanthanide Ions Doping: Synthesis, Downshifting, and Upconversion Luminescence Properties for Multimode Anticounterfeiting.

A new bismuth-based host material, i.e., Sr2BiF7, is explored in this work. Undoped and lanthanide ion-doped Sr2BiF7 nanomaterials are prepared using a simple coprecipitation technique at 120 °C. The undoped nanomaterials exhibit a blue color under 365 nm excitation. The downshifting and upconversion photoluminescent properties of Er and Yb codoped Sr2BiF7 nanomaterials are investigated. The optimum up-conversion luminescence is produced by nanomaterials doped with 5% Yb3+ and 0.2% Er3+. These nanomaterials show blue and magenta colors upon excitation at 365 and 395 nm wavelengths, respectively. Sr2BiF7 material doped with Er3+ shows green emission, while the codoped Er3+, Yb3+ nanomaterials exhibit an orange-red color under 980 nm light. A specific amount of polyvinyl chloride (PVC) is used for producing luminescent ink with these nanoparticles for multimode anticounterfeiting applications. The letters and patterns written with luminescent ink based on Er3+, Yb3+ doped nanomaterials show blue, magenta, and orange-red colors under 365, 395, and 980 nm light, respectively. These results establish that this material can be effectively used as a multimode photoluminescent covert tag to combat counterfeiting.

Influence of Host Lattice Ions on the Dynamics of Transient Multiband Upconversion in Yb-Er Codoped NaLnF4 and LiLnF4 Microcrystals (Ln: Y, Lu, Gd).

Inorganic host matrices provide a tunable luminescence environment for lanthanide ions, allowing for the modulation of upconversion luminescence (UCL) properties. AREF4 (A = alkali metal, RE = rare earth) have a low phonon energy and a high optical damage threshold, making them widely used as the host matrix for UCL materials. However, the impact mechanism of alkali metal ions and lanthanide lattice ions on transient UCL dynamics in AREF4 remains unclear. This study utilized a high-power nanosecond-pulsed laser at 976 nm to excite Yb-Er codoped NaLnF4 and LiLnF4 (Ln: Y, Lu, and Gd) microcrystals (MCs). All samples exhibit multiband emission, and the transient UC dynamics are discussed in detail. Compared with LiLnF4, NaLnF4 has higher UC efficiency and red to green (R/G) ratio. Lanthanide ions (Y, Lu, and Gd) affect the energy transfer (ET) distance in Yb-Er codoped systems, thereby altering UC efficiency and the R/G ratio. The energy level coupling between Gd3+ and Er3+ prolongs the duration of the UC emission. Specifically, the red emission lifetime of NaGdF4 is five times longer than that of NaYF4. Our research contributes to exploring excellent alternative host matrices for NaYF4 in the fields of rapid-response optoelectronic devices, micro-nano lasers, and stimulated emission depletion (STED) microscopy.

Straightforward fabrication of luminescent-magnetic GdF3:Yb3+, Ho3+@void@SiO2 wire-in-tube structured nanofibers

GdF3:Yb3+,Ho3+@void@SiO2 wire-in-tube structured nanofibers (WITSN) with bifunctional characteristic of up-conversion luminescence and magnetism properties are successfully obtained by self-created technique combining monoaxial electrospinning and single-crucible fluorination technology. The products are pure orthorhombic phase. GdF3:Yb3+,Ho3+@void@SiO2 WITSN exhibit large specific surface area and distinctive void space structure. The unique structure of the prepared nanofibers expands the new field of one-dimensional special morphology nanomaterials. In addition, GdF3:Yb3+,Ho3+@void@SiO2 WITSN have the bifunctionality of excellent up-conversion luminescent and paramagnetic properties. Materials have broad applications prospects in display, lighting, optical imaging, magnetic resonance imaging, and biomedicine. This work presents an innovative and high-efficient approach to construct photoluminescence-magnetism bifunctional GdF3:Yb3+,Ho3+@void@SiO2 WITSN, providing a new idea for the preparation of coated structured nanomaterials with excellent multifunctional characteristics.

Maximizing Upconversion Luminescence of Co-Doped CaF₂:Yb, Er Nanoparticles at Low Laser Power for Efficient Cellular Imaging.

Upconversion nanoparticles (UCNPs) are well-reported for bioimaging. However, their applications are limited by low luminescence intensity. To enhance the intensity, often the UCNPs are coated with macromolecules or excited with high laser power, which is detrimental to their long-term biological applications. Herein, we report a novel approach to prepare co-doped CaF2:Yb3+ (20%), Er3+ with varying concentrations of Er (2%, 2.5%, 3%, and 5%) at ambient temperature with minimal surfactant and high-pressure homogenization. Strong luminescence and effective red emission of the UCNPs were seen even at low power and without functionalization. X-ray diffraction (XRD) of UCNPs revealed the formation of highly crystalline, single-phase cubic fluorite-type nanostructures, and transmission electron microscopy (TEM) showed co-doped UCNPs are of ~12 nm. The successful doping of Yb and Er was evident from TEM-energy dispersive X-ray analysis (TEM-EDAX) and X-ray photoelectron spectroscopy (XPS) studies. Photoluminescence studies of UCNPs revealed the effect of phonon coupling between host lattice (CaF2), sensitizer (Yb3+), and activator (Er3+). They exhibited tunable upconversion luminescence (UCL) under irradiation of near-infrared (NIR) light (980 nm) at low laser powers (0.28-0.7 W). The UCL properties increased until 3% doping of Er3+ ions, after which quenching of UCL was observed with higher Er3+ ion concentration, probably due to non-radiative energy transfer and cross-relaxation between Yb3+-Er3+ and Er3+-Er3+ ions. The decay studies aligned with the above observation and showed the dependence of UCL on Er3+ concentration. Further, the UCNPs exhibited strong red emission under irradiation of 980 nm light and retained their red luminescence upon internalization into cancer cell lines, as evident from confocal microscopic imaging. The present study demonstrated an effective approach to designing UCNPs with tunable luminescence properties and their capability for cellular imaging under low laser power.

Upconversion luminescence of pyrochlore structured (A2B2O7) phosphors

The pyrochlore-structured (A2B2O7) compounds have emerged as a focal point in contemporary research and materials science, captivating attention for their intriguing properties such as photoluminescence, superconductivity, ionic mobility, and potential applications in high-temperature barrier coatings. Their potential application in up- or down-conversion photoluminescence further positions them for integration into a myriad of optoelectronic and sensing devices. Building on extensive prior research, this review delves into the upconversion (UC) luminescence properties of numerous pyrochlore-structured host materials (titanates, zirconates, hafnates, and ytterbium pyrochlores), specifically those doped with rare earth ions. While these materials may share similar chemical and structural characteristics, their luminescent capabilities exhibit significant variation upon rare earth ion doping. The phase transitions of various pyrochlore-structured compounds with respect to cation ratio, the relationship between crystal structure, doping concentrations, and UC luminescent properties in pyrochlore-structured compounds are summarized in detail. Through controlled doping strategies and structural adjustments, researchers have been able to tailor the luminescence properties of pyrochlore structured compounds to meet specific application requirements. The intricate exploration of the UC luminescence properties of pyrochlore-structured compounds, especially when doped with rare earth ions, showcases the rich potential for these materials in a wide array of applications across various fields, from advanced sensing technologies to innovative optoelectronic devices, paving the way for exciting advancements in materials science and beyond.

Photoluminescence Confocal Mapping of a Novel Nd3+/Yb3+: Zn2SiO4 Composite thin film on Si (100) Substrate Utilizing a 980nm Pumping Source.

A fixed Nd3+ and varied Yb3+ ion concentration were incorporated in a Zinc-Silicate (SZNYX) composite solution using ex-situ sol-gel solution to fabricate a novel thin film (TF) on Si (100)-substrate. The upconversion luminescence (UCL) spectra of the thin films were measured under 980nm laser excitation, with the most optimized result for Yb3+ ion concentration of 1.5mol%. Additionally, a 2-D photoluminescence (PL) confocal mapping of the SZNY15-TF material confirmed uniform PL distribution throughout the space under the same excitation wavelength. Structural characterization via XRD revealed the tetragonal Zn2SiO4 nano-crystalline nature of the film at three distinct annealing temperatures. Morphological characterization using the Field-emission scanning electron Microscope (FESEM) coupled with energy dispersion spectrometer (EDS) affirmed the nanoflower structure and the purity of doping purity in the samples, respectively. These findings collectively confirm the promising UCL properties of the SZNYX-TF samples, suggesting potential applications in photonic.

A novel single near-infrared luminescence of negative thermal quenching materials for optical temperature measurement

In recent years, upconversion (UC) luminescence has gained attention due to its unique optical properties, and the thermal response spectral characteristics of these materials have been widely utilized in various fields including temperature sensing and biomedical research. However, the photoluminescence (PL) intensity of most rare earth ions doped phosphors decreases with increasing temperature, and the visible fluorescence emission penetration is still limited. In the work, the pure phase of Yb3+ and Er3+ ions co-doped Sc2Mo3O12 was successfully prepared. The Sc2Mo3O12: Yb3+, Er3+ sample showed a single emission of UC near-infrared (NIR) light. The optimum doping concentrations of 0.2 for Yb3+ ions and 0.01 for Er3+ ions were achieved. The possible upconversion luminescence (UCL) mechanism was investigated by analysing the UCL spectra, the down-shift (DS) excitation and emission spectra of Sc2Mo3O12: Yb3+, Er3+ phosphor. The excitation path of NIR emission is mainly through Er3+ from 2H11/2 to 4I9/2 energy level. What's more, the temperature-dependent near-infrared UCL properties of sample is explored in the temperature range from 323 K to 673 K. The enhancement of upconversion luminescence intensity shows a linear relationship with increasing temperature. The study paves a new way for non-contact optical temperature measurement with single near-infrared UCL emission.

The role of thickness on the structural and luminescence properties of Y2O3:Ho3+, Yb3+ upconversion films

The structural, surface, and upconversion (UC) luminescence properties of Y2O3:Ho3+,Yb3+ films grown by pulsed laser deposition, for different numbers of laser pulses, were studied. The crystallinity, surface, and UC luminescence properties of the thin films were found to be highly dependent on the number of laser pulses. The X-ray powder diffraction analysis revealed that Y2O3:Ho3+,Yb3+ films were formed in a cubic structure phase with an Ia 3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{3 }$$\\end{document} space group. The thicknesses of the films were estimated by using cross-sectional scanning electron microscopy, depth profiles using X-ray photoelectron spectroscopy (XPS), and the Swanepoel method. The high-resolution XPS was used to determine the chemical composition and oxidation states of the prepared films. The UC emissions were observed at 538, 550, 666, and 756 nm, assigned to the 5F4 → 5I8, 5S2 → 5I8, 5F5 → 5I8, and 5S2 → 5I7 transitions of the Ho3+ ions. The power dependence measurements confirmed the involvement of a two-photon process in the UC process. The color purity estimated from the Commission International de I’Eclairage coordinates confirmed strong green UC emission. The results suggested that the Y2O3:Ho3+,Yb3+ UC transparent films are good candidates for various applications, including solar cell applications.

Up-Conversion Luminescence and Optical Temperature Sensing Properties of NaLuF4:Yb3+/Ho3+ Micron-Sized Crystals at Low Temperature.

Non-contact temperature sensors utilising the fluorescence intensity ratio and the unique up-conversion (UC) luminescence of rare-earth ions have numerous benefits; however, their operational temperature range has remained limited. In this study, NaLuF4:Yb3+/Ho3+ samples were prepared by the hydrothermal method. The samples exhibited exceptional UC luminescence properties at low temperatures. The intensity of the green emission (with peak wavelengths of 540 and 546 nm) gradually decreased with increasing temperature, and the green emissions showed a unique change at low temperatures. In addition, we studied the dependence of the UC luminescence intensity on the excitation power and the variation in the decay lifetime with temperature. The experiments revealed excellent luminous performance and significantly enhanced sensitivity at low temperatures; the maximum absolute sensitivity Sa and relative sensitivity Sr of the 540 and 546 nm thermally coupled energy levels were 1.02% and 0.55% K-1, respectively. The potential temperature sensing properties of Yb3+/Ho3+-co-doped NaLuF4 makes it suitable for temperature sensing applications at temperatures as low as 30 K. This study offers a novel approach for the advancement of temperature sensing technology at low temperatures.

Co-precipitation synthesis and thermally enhanced upconversion luminescence properties of ScPO4:Yb3+/Er3+ phosphors for temperature sensing

A series of ScPO4:Yb3+/Er3+ upconversion luminescent (UCL) materials with different ytterbium and erbium doping concentrations have been synthesized by a co-precipitation method. Concentration-dependent UCL spectra revealed that the optimal composition was realized for the 15 at%Yb3+ and 1.0 at% Er3+-doping concentration with a strong UCL. Temperature-dependent UCL spectra of ScPO4:Yb3+/Er3+ phosphors indicate that this phosphor possesses thermally enhanced UCL properties. Under the excitation of 980 nm laser, ScPO4:Yb3+/Er3+ can emit intense green and red located at 526/550 nm and 668 nm attributed to the characteristic transitions 2H11/2/4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 of the Er3+ ion, respectively. In addition, the temperature sensing properties of the samples were investigated based on the thermally coupled energy levels (2H11/2 and 4S3/2) of Er3+. In the temperature range of 298∼573 K, the best relative sensitivity (Sr) is 1.28 %/K at 298 K. The above results indicate that ScPO4:Yb3+/Er3+ phosphors have excellent UCL performance and can be applied in luminescence display and temperature sensing.

Upconversion luminescence and optical thermometry properties of glass ceramics embedded with YbOF: Er3+ nanocrystals

Upconversion luminescence and optical thermometry properties of glass ceramics embedded with YbOF: Er3+ nanocrystals

Improved thermometry sensitivity of red-emitting SrGd2O4:Er3+,Yb3+ phosphors using novel NTCL-FIR technology based on 2H11/2 and 4F9/2

In this work, the upconversion luminescence (UCL) and temperature-sensing properties of SrGd2O4 phosphors doped with Er3+, Yb3+ were investigated. The UCL performance was studied by adjusting the doping concentrations of Er3+, Yb3+. It can be found that the intensity of red UCL is effectively improved by doping Yb3+ ions. The band structures of SrGd2O4, SrGd2O4:5 mol%Er3+, and SrGd2O4:5 mol%Er3+,15 mol%Yb3+ were calculated using the density functional theory (DFT) to verify the experimental results. The thermal sensitivity of SrGd2O4:5 mol%Er3+,15 mol%Yb3+ phosphors was studied using the novel fluorescence intensity ratio of non-thermally coupled energy levels (NTCL-FIR) technique based on the 2H11/2 and 4F9/2 energy levels. The analytical results reveal that the maximum values of Sr are 1.69%/K (300 K), 1.18%/K (300 K) and 1.47%/K (300 K) respectively under 915, 980 and 1550 nm excitations. The Sr values of novel NTCL-FIR are compared with that of thermal coupling of energy level (TCL) and other studies in the same field. The results show that the thermometry sensitivity of red-emitting UCL materials can be enhanced by using the novel NTCL-FIR technique. In addition, the intense red UCL of SrGd2O4:Er3+,Yb3+ phosphors have the advantage of deeply penetrating biological tissues. Therefore, the combination of novel NTCL-FIR and red-emitting SrGd2O4:Er3+,Yb3+ phosphors could be conducive to temperature monitoring in vivo.