Multicolor upconversion emission and highly optical temperature sensing based on lanthanide-doped double perovskite Sr2LaNbO6 phosphors

Here we adopt trivalent lanthanide (Ln³⁺ = Er³⁺, Er³⁺/Ho³⁺, and Yb³⁺/Tm³⁺) doped Sr₂LaNbO₆ (SLNO) as novel upconversion luminescence (UCL) materials for achieving UCL and optical temperature sensing under 980 nm excitation. Specifically, Er³⁺ single doped Sr₂LaNbO₆ phosphors present bright high-purity green emission under the 980 nm excitation. While co-doping with the Ho³⁺ ions, the component of red emission from Er³⁺ ions increases significantly and sample show a remarkable enhancement of luminescent intensity relative to SLNO:Er³⁺ sample. The above-mentioned phosphors and Yb³⁺/Tm³⁺ co-doped phosphor (blue emission) successfully achieve high-purity trichromatic UCL and mixed white light output in the same host. Furthermore, the temperature sensing performance of the SLNO:Er³⁺/Ho³⁺ phosphor based on the fluorescence intensity ratio (FIR) is systematically studied for the first time. The temperature sensing based on the non-thermal coupling levels (NTCLs) exhibit higher sensitivity than that based on the thermal coupling levels (TCLs). The maximum absolute and relative sensitivity for ⁴F_9/2/⁴I_9/2 NTCLs reach 0.16803 K^?1 at 427 K and 0.01591 K^?1 at 641 K, respectively. Interestingly, NIR emission of ⁴I_9/2 → ⁴I_15/2 transition presents a thermal enhancement, while visible emissions show thermal quenching. These results indicate that the Ln³⁺ doped Sr₂LaNbO₆ UCL phosphors have potential applications in the fields of non-contact temperature sensors, full-color displays, and anti-counterfeiting.     

Dual-mode dichromatic SrBi4Ti4O15: Er3+ emitting phosphor for anti-counterfeiting application

Fluorescent materials have been widely used for anti-counterfeiting of important documents and currencies, wherein their anti-counterfeit abilities could be improved through multi-mode excitation. Herein, dual-mode-excited double-colour-emitting Er³⁺doped SrBi₄Ti₄O₁₅ up-conversion (UC) phosphors (SBTO: Er³⁺) were synthesised, and their UC spectra included green (2H11/2/4S3/2 → 4I15/2) and red (4F9/2 → 4I15/2) emissions from Er3+ ions under 980 or 1550 nm excitation. However, the green emission colour of phosphors was independent of dopant concentration under 980 nm laser irradiation; whereas the final emission colour was dominated by red emission and significantly affected by contents of Er3+ under 1550 nm excitation. These observations demonstrated potential application in dual-mode double-colour anti-counterfeiting. The possible UC mechanisms and emission characteristics of the phosphors using different 980 and 1550 nm irradiation source were contrastively investigated, and some fluorescent security patterns were also designed to demonstrate the potential applications in anti-counterfeiting and concealing important information.     

Color-tunable up-conversion emission from Yb3+/Er3+/Tm3+/Ho3+ codoped KY(MoO4)2 microcrystals based on energy transfer

Tunable up-conversion luminescent material KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) has been synthesized by a typical hydrothermal process. Under 980 nm laser diode (LD) excitation, the emission intensity and the corresponding luminescence colors of KY(MoO₄)₂: Yb³⁺, Ln³⁺ (Ln=Er, Tm, Ho) have been investigated in detail. The energy transfer from the Yb³⁺ sensitizer to Ho³⁺, Er³⁺ and Tm³⁺ activators plays an important role in the development of color-tunable single- phased phosphors. The emission intensity keep balance through control of the Ho³⁺ co-doping concentrations, white light was experimentally shown at KY(MoO₄)₂: 20 mol% Yb³⁺, 0.8 mol% Er³⁺, 0.5 mol% Tm³⁺, 1.0 mol% Ho³⁺ phosphor with further calcination at 800 °C for 4 h under 980 nm laser excitation. The color tunability, high quality of white light and high intensity of the emitted signal make these up-conversion (UC) phosphors excellent candidates for applications in solid-state lighting.     

Concentration effects on the upconversion luminescence in Ho3+/Yb3+ co-doped NaGdTiO4 phosphor

Ho³⁺/Yb³⁺ co-doped NaGdTiO₄ phosphors were synthesized by a solid-state reaction method. The upconversion (UC) luminescence characteristics excited by 980 nm laser diode were systematically investigated. Bright green UC emission centered at 551 nm accompanied with weak red and near infrared (NIR) UC emissions centered at 652 and 761 nm were observed. The dependence of UC emission intensity on excitation power density showed that all of green, red and NIR UC emissions are involved in two-photon process. The UC emission mechanisms were discussed in detail. Concentration dependence studies indicated that Ho³⁺ and Yb³⁺ concentrations had significant influences on UC luminescence intensity and the intensity ratio of the red UC emission to that of the green one. Rate equations were established based on the possible UC mechanisms and a theoretical formula was proposed to describe the concentration dependent UC emission. The UC luminescence properties of the presented material was evaluated by comparing with commercial NaYF₄:Er³⁺, Yb³⁺ phosphor, and our sample showed a high luminescence efficiency and good color performance, implying potential applications in a variety of fields.     

Preparation,luminescence properties,and application of temperature sensing and anti-counterfeiting of La2MgTiO6:Yb3+/Ln3+/Mn4+

The doping of transition metal ions in the up-conversion (UC) luminescent material doped with Yb³⁺/Ln³⁺ is a facile way to increase their UC luminescence intensities and alter their colors. In this study, La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ (Ln³⁺ = Er³⁺, Ho³⁺, and Tm³⁺) phosphors showing excellent luminescence properties were prepared by a solid-state method. The sensitivity of the La₂MgTiO₆:Yb³⁺/Ln³⁺/Mn⁴⁺ phosphor was double that without Mn⁴⁺, because Mn⁴⁺ affects the UC emissions of Ln³⁺ via energy transfer between these ions. Moreover, Mn⁴⁺ also acts as a down-conversion activator, which can combine with UC ions to achieve multi-mode luminescence at different wavelengths. Under 980 nm excitation, these samples emit green light (from Er³⁺ and Ho³⁺) and blue light (from Tm³⁺). In contrast, under 365 nm excitation, they emit red light (from Mn⁴⁺). Further testing revealed that the La₂MgTiO₆:Yb³⁺/Mn⁴⁺/Ln³⁺ phosphors have potential applications in temperature sensing and anti-counterfeiting.     

Warm white-light generation in Ca9MgNa(PO4)7:Sr2+, Mn2+, Ln (Ln=Eu2+, Yb3+, Er3+, Ho3+, and Tm3+) under near-ultraviolet and near-infrared excitation

To obtain warm white-light emission, a series of Ca₉MgNa(PO₄)₇:Sr²⁺, Mn²⁺, Ln (Ln=Eu²⁺, Yb³⁺, Er³⁺, Ho³⁺, and Tm³⁺) phosphors were designed and their photoluminescence properties under near-ultraviolet and near-infrared excitation were studied. For near-ultraviolet excitation, blue-white emission is produced initially in the Eu²⁺ single-doped Ca₉MgNa(PO₄)₇, whose excitation band can well match with the near ultraviolet LED chip. By introducing Sr²⁺ ions into Ca₉MgNa(PO₄)₇:Eu²⁺, the Eu²⁺ emission band beyond 500 nm is enhanced obviously. Correspondingly, the emitting light color is tuned to nearly white. To generate warm white light further, Mn²⁺ is doped into the Ca_8.055MgNa(PO₄)₇:0.045Eu²⁺, 0.9Sr²⁺ and the correlated color temperature is decreased largely. For near-infrared excitation, the green, red, and blue emissions have been obtained in the Yb³⁺-Er³⁺, Yb³⁺-Er³⁺, and Yb³⁺-Er³⁺ co-doped Ca₉MgNa(PO₄)₇ phosphors, respectively. And warm white light is also produced in the Ca₉MgNa(PO₄)₇:Yb³⁺, Er³⁺, Ho³⁺, Tm³⁺ under 980 nm excitation.     

Tailorable Multicolor Up‐conversion Emissions in Tm3+/Ho3+/Yb3+ Co‐Doped LiLa(MoO4)2

Using a modified sol–gel method, LiLa(MoO₄)₂: Tm³⁺/Ho³⁺/Yb³⁺ phosphors with tailorable up‐conversion (UC) emission colors were prepared. Under the excitation of a 980 nm laser diode, up‐conversion red and green emissions in Ho³⁺/Yb³⁺ co‐doped and blue emission in Tm³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂ were observed, respectively. The intensities of the RGB (red, green, and blue) emissions could be controlled by varying concentrations of Tm³⁺ or Ho³⁺, and the optimal composition was also determined. In Tm³⁺/Ho³⁺/Yb³⁺ co‐doped LiLa(MoO₄)₂, the UC emission colors could be tuned from blue through white to yellow by adjusting the concentrations of Tm³⁺ or Ho³⁺. The UC excitation mechanisms were also investigated based on the power dependence of UC luminescence intensity.     

Upconversion thermal enhancement of 2H11/2→4I15/2 of Er3+ and blue emission of impurity Tm3+ in Sr3(PO4)2:Er3+/Yb3+

A series of Sr_2.99-x(PO₄)₂:.01Er³⁺/xYb³⁺ (x = .02, .04, .06, .08, .10) phosphors in the presence of impurity Tm³⁺ were synthesized by high temperature solid-state method, and X-ray diffraction results show that these samples are pure R-3 m(166) space group phase. The upconversion luminescence (UCL) of Er³⁺ and impurity Tm³⁺ under 980-nm laser excitation were investigated, and the results show that the intense blue UCL of impurity Tm³⁺ and thermal enhancement of ²H_11/2→⁴I_15/2 of Er³⁺ simultaneously exist. When Er³⁺ doping concentration is kept at .01, both the blue UCL intensity of impurity Tm³⁺ and green and red UCL intensity of Er³⁺ reach the maximum at Yb³⁺ doping concentration of .08. The thermal enhancement effect of ²H_11/2→⁴I_15/2 of Er³⁺ was observed as high as 3.27 times from 303 to 723 K, which is because of lattice distortion and phonon-assisted transition. In addition, the optical temperature performance of Sr_2.91(PO₄)₂:.01Er³⁺/.08Yb³⁺ sample was studied, and the maximum absolute temperature sensitivity was calculated as .00623 K⁻¹ at 538 K. This study suggests that Sr₃(PO₄)₂:Er³⁺/Yb³⁺ phosphors in the presence of impurity Tm³⁺ have a promising application prospect as optical temperature sensor at high temperature.     

Abnormal upconversion luminescence induced by defects and Er3+–Yb3+ distance change in Cs3GdGe3O9:Er3+/Yb3+ phosphors

A series of Er³⁺/Yb³⁺ co-doped Cs₃GdGe₃O₉ (CGG) phosphors were prepared by solid-phase sintering method, and the microstructure and upconversion luminescence (UCL) properties were tested by variable-temperature X-ray diffractometry and variable-temperature spectrometer. Abnormal UCL phenomena were found, which include UCL intensity continuously increasing under 980 nm laser continuous irradiation and UCL thermal enhancement. After 10 min of continuous irradiation by 980 nm laser at 513 K, the UCL intensity increased 2.91 times compared with the initial UCL intensity. The phenomenon is due to the electron releasing of host defects. The green UCL intensity of CGG:0.1Er³⁺/0.2Yb³⁺ decreases at 303–423 K and increases at 423–723 K, which reaches 13.23 times compared with that at 423 K. The phenomenon is due to Er³⁺–Yb³⁺ distance change by temperature and phonon-assisted transitions. In addition, the absolute temperature sensitivities of samples are calculated by luminescence intensity ratio technology, the maximum absolute sensitivity of CGG:0.1Er³⁺/0.4Yb³⁺ is 0.00691 K⁻¹ at 546 K, and the maximum relative sensitivity of CGG:0.1Er³⁺/0.1Yb³⁺ is 0.01224 K⁻¹ at 303 K. These results indicate that CGG:Er³⁺/Yb³⁺ phosphors can be used as a high-temperature optical thermometer.     

Spectral pure RGB up-conversion emissions in self-assembled Gd2O3: Yb3+, Er3+/Ho3+/Tm3+ 3D hierarchical architectures

Self-assembled three-dimensional Yb³⁺(Ln = Er, Ho, Tm) co-doped Gd₂O₃ up-converted (UC) phosphors were synthesized by a facile co-precipitation method, and their morphologies and microstructures were investigated by scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. Under the excitation at 980 nm, spectral pure three primary colors red, green and blue (RGB) emissions were respectively achieved in Yb³⁺/Er³⁺, Yb³⁺/Ho³⁺ and Yb³⁺/Tm³⁺ co-doped Gd₂O₃ phosphors, in which spectral color purities were tuned by adjusting the doping concentration, annealing temperature, excitation power density and the pulse-width of 980 nm laser. These results provide deeper insights into modulating spectral color purities of up-converted emission, and the potential applications of spectrally pure RGB up-converted materials in fingerprint recognition and multi-color printing were also investigated.     

Preparation and photoluminescence enhancement of Au nanoparticles with ultra-broad plasmonic absorption in glasses

The metal nanoparticles with ultra-broad localized surface plasmonic resonance (LSPR) absorption have been widely used to enhance the up conversion luminescence (UCL) of rare-earth doped nanoparticles. However, there have been no reports on the preparation of metal nanoparticles with the ultra-broad LSPR in the glasses. In this work, the gold nanoparticles with the ultra-broad LSPR were prepared for the first time in the rare-earth doped tellurite glasses by the high-temperature melting method, and the influence of ultra-broad LSPR on the UCL of Er³⁺–Yb³⁺ and Er³⁺–Yb³⁺–Nd³⁺ co-doped tellurite glasses was investigated upon 980 and 808 nm excitation, respectively. With the precipitation of the Au NPs, about seven and 12-fold enhancements were obtained for the green and red UCL of Er³⁺–Yb³⁺ co-doped tellurite glasses excited at 980 nm, respectively, and about 5.9 and sevenfold enhancements were observed for the green and red UCL of Er³⁺–Yb³⁺–Nd³⁺ co-doped tellurite glasses excited at 808 nm, respectively. The UCL mechanism related to UCL enhancement was confirmed. The results demonstrated that the enhanced excitation field and the increasing rate of radiative decay were responsible for the enhancement of UCL.     

Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808 nm

As alternatives to Yb³⁺-sensitized up-conversion (UC) materials excited at 980 nm, Nd³⁺-sensitized UC phosphors irradiated by 808 nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from ⁵F₅→⁵I₈ and ⁵F₄/⁵S₂→⁵I₈ transitions of Ho³⁺ appeared in Nd³⁺/Yb³⁺/Ho³⁺ tri-doped NaLa(MoO₄)₂ through successive energy transfer Nd³⁺→Yb³⁺→Ho³⁺ under 808 nm excitation, in which Yb³⁺ ions were proven to be the energy transfer bridge between Nd³⁺ and Ho³⁺ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb³⁺, pulse width of the excitation laser and the addition of Ce³⁺ ion, which depends on the different population pathways to the green and red emitting states of Ho³⁺. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.     

BiLaWO6: Er3+/Tm3+/Yb3+ phosphor: Study of multiple fluorescence intensity ratiometric thermometry at cryogenic temperatures

Highly thermally stable Er³⁺/Tm³⁺/Yb³⁺ tri-doped bismuth lanthanum tungstate phosphors were prepared by high temperature solid-state reaction method. The structural and morphological properties of the prepared phosphors were analysed by X-ray diffraction (XRD), Raman spectroscopy and Scanning electron microscopy (SEM) coupled with energy dispersion spectrum (EDS). Visible upconversion (UC) luminescence was measured by exciting the phosphors with 980 nm laser radiation. The dependence of the UC intensity of each emission band of Er³⁺ and Tm³⁺ ions as a function of temperature in the range from 30 to 300 K was monitored. Fluorescence intensity ratios (FIR) of thermally coupled levels (TCL) and non-thermally coupled levels (NTCL) were analysed and verified with appropriate theoretical validation. The absolute (S_A) and relative sensitivities (S_R) were estimated and compared with the reported systems. In the present case of BiLaWO₆: Er³⁺/Tm³⁺/Yb³⁺, S_R (0.43 % K^?1) related to TCL of Er³⁺ UC is found to have maximum sensitivity compared to any of the NTCL combinations at 300 K. From this study we inferred that the S_R values estimated from NTCL are smaller than that of TCL involved in BLW: Er³⁺/Tm³⁺/Yb³⁺ phosphor. The temperature dependent CIE color coordinates were also evaluated in the cryogenic temperature region.     

Down-conversion from Er3+-Yb3+ codoped CaMoO4 phosphor: A spectral conversion to improve solar cell efficiency

The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er³⁺ and Yb³⁺ in CaMoO₄:Er³⁺, Yb³⁺ phosphors. We have successfully synthesized a series of Er³⁺ doped and Yb³⁺ codoped CaMoO₄ phosphors by hydrothermal method. The down-conversion of Er³⁺-Yb³⁺ combination with CaMoO₄ phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er³⁺ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to ⁴S_3/2→⁴I_15/2 transition. The addition of Yb³⁺ into Er³⁺ doped CaMoO₄ attribute an emission at 980 nm due to ²F_5/2→²F_7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er³⁺ to Yb³⁺ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb³⁺ ion. The lifetime measurement also reveals the energy transfer from Er³⁺ to Yb³⁺ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively.     

Intense 2.85 μm mid-infrared emissions in Yb3+/Ho3+ codoped and Yb3+/Er3+/Ho3+ tridoped TBLL fluorotellurite glasses and their energy transfer mechanism

Yb³⁺/Ho³⁺ codoped and Yb³⁺/Er³⁺/Ho³⁺ tridoped TeO₂–BaF₂–LaF₃–La₂O₃ (TBLL) fluorotellurite glasses with low OH^? absorption (0.026 cm^-1), high glass transition temperature (434 °C) and low phonon energy (784 cm^-1) were prepared. Their mid-infrared fluorescence properties and related energy transfer (ET) mechanism were studied under 980 nm excitation. A strong emission at 2.85 μm was realized in Yb³⁺/Ho³⁺ codoped tellurite glass, which was attributed to the high-efficiency ET from Yb³⁺ ions to Ho³⁺, and the ET efficiency was 91.1%. Further introduction of Er³⁺ ions induced stronger 2.85 μm emission, and the ET efficiency was improved to 96.2%, ascribed to the establishment of more ET channels and Er³⁺ ions playing the role of ET bridge between Yb³⁺ and Ho³⁺ ions. These results indicate that the Yb³⁺/Er³⁺/Ho³⁺ tridoped tellurite glass could be a hopeful gain medium material for the ～3 μm fiber laser.     

La2O2SO4:RE/Yb new phosphors for near infrared to visible and near infrared upconversion luminescence (RE=Ho,Er, Tm)

The 3 new upconversion (UC) phosphors of La₂O₂SO₄:RE/Yb (RE=Ho, Er, and Tm, respectively) were derived via facile dehydration of their layered hydroxide precursors that were hydrothermally synthesized at 100°C. Rietveld XRD refinement found contracting cell dimension with decreasing RE³⁺ size, confirming the direct crystallization of solid solution. The Er³⁺ and Ho³⁺ activators both exhibited simultaneous green and red (dominant) emissions under 978‐nm near‐infrared (NIR) laser excitation (NIR‐Vis UC). Particularly, Tm³⁺ produced a Gaussian‐shaped pure NIR emission band at ~812 nm via its ³H₄ → ³H₆ transition (NIR‐NIR UC), which is highly desired for NIR biological application. Analysis of the excitation‐power dependent UC properties manifested a 3‐photon mechanism for the 3 phosphors, and the possible photon reactions leading to UC were illustrated.     

Yb3+/Er3+ co-doped Gd2Te4O11 nanosheets with intrinsic polarity: One-step hydrothermal synthesis and upconverted optical temperature measuring ability

The digadolinium tellurite phosphors of Gd₂Te₄O₁₁(GTO):Yb³⁺/Er³⁺ have been successfully synthesized as upconversion luminescence (UCL) materials via one-step hydrothermal method. The crystal structure, morphology, and upconversion luminescence property were systematically characterize by XRD, SEM, and spectroscopy techniques. The Rietveld refinements of crystal structure were carried out on the XRD patterns and the feature of crystal structure was analyzed. Under the 980 nm NIR excitation, these materials showed very bright upconverted emissions. The concentrations of Yb³⁺ and Er³⁺ were optimized and the strongest upconverted emissions were achieved in the GTO:15%Yb³⁺/1%Er³⁺. The possible energy transfer mechanism of UCL was proposed based upon the analysis of power-dependent UCL and fluorescence kinetics. Furthermore, the fluorescence intensity ratio (FIR) derive from the two thermally coupled energy levels (²H_11/2 and ⁴S_3/2) of Er³⁺ was employed as indicator for temperature measurement. The maximum absolute sensitivity can be achieved to be 7.34 × 10^?3 K^?1 at 501 K. This material exhibited good reliability and repeatability in optical temperature measurement, which could be a novel promising candidate for noncontact temperature sensors.     

Up-conversion phosphor plate for white lighting device using NIR excitation source

Upconversion phosphors have numerous advantages compared to down conversion phosphor materials, such as a weak background interface, low excitation energy, sharp emission lines, and long lifetimes. Conventionally, blue laser diodes are used to obtain strong white light by combining green- and red-emitting phosphors. The blue-excited white-light-emitting devices can be harmful when the blue light penetrates directly into the human body. However, lower energy excited lighting devices does not harm the human body because of their low-energy photons are compatible with the biologically safe window. Hence, we present a prototype device that converts invisible near-infrared light into visible white light. For this, we synthesized orange-emitting Y₂O₃:Er³⁺, Yb³⁺ and blue-emitting Y₂O₃:Tm³⁺, Yb³⁺ upconversion phosphors using a solid-state reaction. Using these, phosphor-in-glass (PiG) samples with sintered glass frit were prepared to investigate their optical behavior under low-excitation energy. The emission color from the stacked PiGs depends on the color balance between the activator ions of Er³⁺, Tm³⁺, and Yb³⁺, and their balance is optimized to obtain a white light. The results might pave the way for designing safe white-light-emitting devices using a low-energy excitation source.     

Thermal enhancement of up-conversion luminescence in Lu2W2.5Mo0.5O12: Er3+, Yb3+ phosphors

Lu₂W_2.5Mo_0.5O₁₂: Er³⁺/Yb³⁺ phosphors were synthesized through high temperature solid state method. Under 980 nm laser excitation, the Lu₂W_2.5Mo_0.5O₁₂: Er³⁺/Yb³⁺ compounds show thermal enhancement of up-conversion luminescence (UCL), which is attributed to the lattice contraction and distortion from negative thermal expansion (NTE) of Lu₂W_2.5Mo_0.5O₁₂ host enhancing the energy transfer of Yb³⁺ to Er³⁺, eliminating the energy transfer of Er³⁺ to Er³⁺ through Er³⁺ single-doped Lu₂W_2.5Mo_0.5O₁₂ phosphors without thermal enhancement of UCL. The green luminescence intensities at 693 K of the Lu_1.98-xW_2.5Mo_0.5O₁₂: 0.02Er³⁺, xYb³⁺ (x = 0.2, 0.3, 0.4) samples are 4.6, 4.3 and 7.0 times as that of 302 K, respectively. And through fluorescence intensity ratio (FIR) technique, the corresponding maximum absolute sensitivities are 0.00741, 0.00744 and 0.00723, respectively. The green monochromaticity of UCL spectra in Er³⁺/Yb³⁺ co-doped samples increase with the increasing of temperature, and the possible UCL mechanism with temperature was discussed. The results indicate that the Lu₂W_2.5Mo_0.5O₁₂: Er³⁺/Yb³⁺ phosphors can be applied at a high temperature as optical thermometer with a good green monochromaticity.