Role of Yb and Tm ions in upconversion emission of Tb under 798 and 980 nm laser excitations in Tb-Tm-Yb doped tellurite glass

Upconversion emission and energy transfer processes in singly, doubly and triply doped tellurite glasses have been studied under 798 and 980 nm laser excitations. Emissions have been observed at 482, 544, 584, 655 nm and at 477, 655, 698, 800 nm corresponding to Tb³⁺: ⁵D₄ → ⁷F₆, ⁷F₅, ⁷F₄, ⁷F_J (J = 0, 1, 2, 3) and Tm³⁺: ¹G₄ → ³H₆, ¹G₄ → ³F₄, ³F₃ → ³H₆, ³H₄ → ³H₆ transitions, respectively. Among Tm³⁺, Yb³⁺and Tb³⁺ ions only Tm³⁺ has a ground state absorption at 798 nm excitation due to ³H₄ ← ³H₆ transition. For 980 nm excitation only Yb³⁺ can absorb the incident radiation. However, for both types of excitations, emission from all the three ions Tb, Yb and Tm has been observed. Possible mechanisms are proposed as follows: under 798 nm excitation Tm³⁺ ions are excited which excite Yb³⁺ ions through energy transfer. Finally “cooperative energy transfer” from a pair of Yb³⁺ ions to Tm³⁺ and Tb³⁺ ions takes place. Under 980 nm excitation Yb³⁺ ions absorb the incident energy and excite Tm³⁺ and Tb³⁺ ions via cooperative energy transfer. Variation of emission intensity with the ion concentrations of Yb³⁺, Tm³⁺ and Tb³⁺ has been studied. The lifetime of the ¹G₄ level has also been measured.     

Spectral analysis of Pr-, Sm- and Dy-doped transparent GeO2-BaO-TiO2 glass ceramics

In this paper, we present the photoluminescence properties of Pr³⁺-, Sm³⁺- and Dy³⁺-doped germanate glasses and glass ceramics. From the X-ray diffraction measurement, the host glass structure was determined. These glasses have shown strong absorption bands in the near-infrared (NIR) region. Compared to Pr³⁺-, Sm³⁺- and Dy³⁺-doped glasses, their respective glass ceramics have shown stronger emissions due to the Ba₂TiGe₂O₈ crystalline phase. For Pr³⁺-doped glass and glass ceramic, emission bands centered at 530 nm (³P₀→³H₅), 614 nm (³P₀→³H₆), 647 nm (³P₀→³F₂) and 686 nm (³P₀→³F₃) have been observed with 485 nm (³H₄→³P₀) excitation wavelength. Of them, 647 nm (³P₀→³F₂) has shown bright red emission. Emission bands of ⁴G_5/2→⁶H_5/2 (565 nm), ⁴G_5/2→⁶H_7/2 (602 nm) and ⁴G_5/2→⁶H_9/2 (648 nm) for the Sm³⁺:glass and glass ceramic, with excitation at ⁶H_5/2→⁴F_7/2 (405 nm) have been recorded. Of them, ⁴G_5/2→⁶H_7/2 (602 nm) has shown a bright orange emission. With regard to the Dy³⁺:glass and glass ceramic, a bright fluorescent yellow emission at 577 nm (⁴F_9/2→⁶H_13/2) has been observed, apart from ⁴F_9/2→⁶H_11/2 (667 nm) emission transition with an excitation at 454 nm (⁶H_15/2→⁴I_15/2) wavelength. The stimulated emission cross-sections of all the emission bands of Pr³⁺, Sm³⁺ and Dy³⁺:glasses and glass ceramics have been computed based on their measured full-width at half-maxima (FWHM, Δλ) and lifetimes (τ_m).     

Spectroscopic investigation of Tm:TeO2-WO3 glass

We studied the spectroscopic characteristics of telluride glass with the host composition (0.85)TeO₂-(0.15)WO₃, containing 0.25 and 1.0 mol% thulium oxide (Tm₂O₃). By analyzing the absorption spectra with the Judd-Ofelt theory, the average radiative lifetimes of 305±7.5 μs and 1.95±0.02 ms were determined for the ³F₄ and ³H₄ levels, respectively. Measured fluorescence lifetime of the ³F₄ level decreased from 218 to 51 μs for the 0.25 and 1.0 mol% Tm₂O₃ doped samples, respectively, indicating the effect of boosted non-radiative decay at higher doping concentrations. A similar trend was observed for the ³H₄ level, where the fluorescence lifetime decreased from 1.86 ms to 350 μs at these concentrations. The quenching of the 1460 nm (³F₄→³H₄) emission in favor of the 1800 nm (³H₄→³H₆) emission due to cross relaxation was further evident in the fluorescence spectra of the samples. The calculated stimulated emission cross sections (3.73±0.1×10⁻²¹ cm² at 1460 nm and 6.57±0.07×10⁻²¹ cm² at 1808 nm) reveal the potential importance of the Tm³⁺:(0.85)TeO₂-(0.15)WO₃ glass for applications in fiber-optic amplifiers and fiber lasers.     

β-Na(Y1.5Na0.5)F6:Tm—A blue upconversion phosphor

A luminescent material β-Na(Y_1.5Na_0.5)F₆ doped with Tm³⁺ was synthesized by a solid-state reaction method for a steady phosphor of blue upconversion. Under the 671 nm laser excitation, the green emission band of 511 nm due to the ¹D₂→³H₅ transition is obtained for the first time, while the ultraviolet emission band is also observed at 368 nm, associated with the ¹D₂→³H₆ transition. Especially, a wide band of blue emissions is obtained at the wavelength region of 440-490 nm, originated mainly from the ¹D₂→³F₄ (450 nm) and ¹G₄→³H₆ (471-487 nm) transitions, which have potential application in tunable solid-state blue laser of Tm³⁺. The upconversion mechanism is explored in terms of the energy-level structures of Tm³⁺ ion and the power dependence of upconverted emission intensity, which is believed to be performed by excited-state absorption.     

Multiphoton ultraviolet and visible upconversion luminescence of TmYb co-doped oxyfluoride glass

The ultraviolet upconversion luminescence of Tm³⁺ ions sensitized by Yb³⁺ ions in oxyfluoride glass when excited by a 975 nm diode laser was studied in this paper. One typical ultraviolet upconversion luminescence lines positioned at 362.3 nm was found. It can be attributed to the five-photon upconversion luminescence transition of ¹D₂ → ³H₆. Several visible upconversion luminescence lines at 451.1 nm, (477.9 nm, 462.5 nm), 648.7 nm, (680.5 nm, 699.5 nm) and (777.5 nm, 800.7 nm) were found also, which results from the fluorescence transitions of five-photon ¹D₂ → ³F₄, three-photon ¹G₄ → ³H₆, three-photon ¹G₄ → ³F₄, two-photon ³F₃ → ³H₆ and two-photon ³H₄ → ³H₆ of Tm³⁺ ion, respectively. The theoretical analysis suggests that the upconversion mechanism of the 362.3 nm ¹D₂ → ³H₆ upconversion luminescence is the cross energy transfer of {³H₄(Tm³⁺) → ³F₄(Tm³⁺), ¹G₄(Tm³⁺) → ¹D₂(Tm³⁺)} and {¹G₄(Tm³⁺) → ³F₄(Tm³⁺), ³H₄(Tm³⁺) → ¹D₂(Tm³⁺)} between Tm³⁺ ions. In addition, the upconversion luminescence of ¹G₄ and ³H₄ state results from the sequential energy transfer {²F_5/2(Yb³⁺) → ²F_7/2(Yb³⁺), ³H₄(Tm³⁺) → ¹G₄(Tm³⁺)} and {²F_5/2(Yb³⁺) → ²F_7/2(Yb³⁺), ³F₄(Tm³⁺) → ³F₂(Tm³⁺)} from Yb³⁺ ions to Tm³⁺ions, respectively.     

Enhanced white light emission in Er/Tm/Yb/Li codoped Y2O3 nanocrystals

Er/Tm/Yb codoped Y₂O₃ nanocrystals and Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals have been synthesized by sol-gel method, bright white light emission has been observed at 976 nm excitation. The blue, green, and red emissions, respectively, arise from the transitions ¹G₄ → ³H₆ of Tm³⁺, ²H_11/2/⁴S_3/2 → ⁴I_15/2, and ⁴F_9/2 → ⁴I_15/2 of Er³⁺ ion. Moreover, after doping Li⁺ ions into Er/Tm/Yb codoped Y₂O₃ nanocrystals, the white light emission increase greatly. CIE coordinate of Er/Tm/Yb/Li codoped Y₂O₃ nanocrystals is X = 0.32 and Y = 0.36 at 10 W/cm² excitation, which is very close to the standard equal energy white light illuminate (X = 0.33, Y = 0.33).     

Enhanced blue-green-red up-conversion and 1.3-μm emission of Pr/Yb-codoped oxyhalide tellurite glasses with PbCl2 doping

We report on the blue-green-red up-conversion spectroscopic properties of Pr³⁺/Yb³⁺-codoped oxyhalide tellurite glasses upon excitation of a conventional 980 nm laser diode (LD). Significant enhancement of the blue-green-red up-conversion emission intensity has been observed with increasing PbCl₂ doping. The up-conversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. The population of the Pr³⁺ upper ³P₀ emitting level was accomplished through a combination of a ground state absorption, energy transfer and excitated state absorption. 1.3-μm emission in the second telecom window originated from Pr³⁺:¹G₄→³H₅ transition has also been investigated upon excitation at 980 nm LD. The measured peak wavelength and full width at half-maximum of the fluorescent are 1335 nm and ∼100 nm, respectively. An enhanced 1.3μm emission with increasing PbCl₂ doping has also been observed. Codoping of Yb³⁺ significantly enhance both the blue-green-red up-conversion emission and 1.3-μm emission intensity by way of a nonradiative Yb³⁺:²F₅→Pr³⁺:¹G₄ energy transfer.     

Efficient blue upconversion emission due to confined radiative energy transfer in Tm-Nd co-doped Ta2O5 waveguides under infrared-laser excitation

Intense blue upconversion emission at 480 nm has been obtained at room temperature in Tm³⁺-Nd³⁺ co-doped Ta₂O₅ channel waveguides fabricated on a Si substrate, when the sample is excited with an infrared laser at 793 nm. The upconversion mechanism is based on the radiative relaxation of the Nd³⁺ ions (⁴F_3/2 → ⁴I_11/2) at about 1064 nm followed by the absorption of the emitted photons by Tm³⁺ ions in the ³H₄ excited state. A coefficient of energy transfer rate as high as 3 × 10⁻¹⁶ cm³/s has been deduced using a rate equation analysis, which is the highest reported for Tm-Nd co-doped systems. The confinement of the 1064 nm emitted radiation in the waveguide structure is the main reason of the high energy transfer probability between Nd³⁺ and Tm³⁺ ions.     

Spectroscopic investigations of Nd-, Er-, Er/Yb-, and Tm-ions doped SiO2-Al2O3-CaF2-GdF3 glasses

This paper reports on the absorption, visible and near-infrared luminescence properties of Nd³⁺, Er³⁺, Er³⁺/2Yb³⁺, and Tm³⁺ doped oxyfluoride aluminosilicate glasses. From the measured absorption spectra, Judd-Ofelt (J-O) intensity parameters (Ω₂, Ω₄ and Ω₆) have been calculated for all the studied ions. Decay lifetime curves were measured for the visible emissions of Er³⁺ (558 nm, green), and Tm³⁺ (650 and 795 nm), respectively. The near infrared emission spectrum of Nd³⁺ doped glass has shown full width at half maximum (FWHM) around 45 nm (for the ⁴F_3/2→⁴I_9/2 transition), 45 nm (for the ⁴F_3/2→⁴I_11/2 transition), and 60 nm (for the ⁴F_3/2→⁴I_13/2 transition), respectively, with 800 nm laser diode (LD) excitation. For Er³⁺, and Er³⁺/2Yb³⁺ co-doped glasses, the characteristic near infrared emission bands were spectrally centered at 1532 and 1544 nm, respectively, with 980 nm laser diode excitation, exhibiting full width at half maximum around 50 and 90 nm for the erbium ⁴I_13/2→⁴I_15/2 transition. The measured maximum decay times of ⁴I_13/2→⁴I_15/2 transition (at wavelength 1532 and 1544 nm) are about 5.280 and 5.719 ms for 1Er³⁺ and 1Er³⁺/2Yb³⁺ (mol%) co-doped glasses, respectively. The maximum stimulated emission cross sections for ⁴I_13/2→⁴I_15/2 transition of Er³⁺ and Er³⁺/Yb³⁺ are 10.81×10⁻²¹ and 5.723×10^-21 cm². These glasses with better thermal stability, bright visible emissions and broad near-infrared emissions should have potential applications in broadly tunable laser sources, interesting optical luminescent materials and broadband optical amplification at low-loss telecommunication windows.     

Temperature-dependent photoluminescence spectra of Er-Tm-codoped Al2O3 thin film

Er-Tm-codoped Al₂O₃ thin films with different Tm to Er concentration ratios were synthesized by cosputtering from separated Er, Tm, Si, and Al₂O₃ targets. The temperature dependence of photoluminescence (PL) spectra was studied. A flat and broad emission band was achieved in the 1.4-1.7 μm and the observed 1470, 1533 and 1800 nm emission bands were attributed to the transitions of Tm³⁺: ³H₄ → ³F₄, Er³⁺: ⁴I_13/2 → ⁴I_15/2 and Tm³⁺: ³F₄ → ³H₆, respectively. The temperature dependence is rather complicated. With increasing measuring temperature, the peak intensity related to Er³⁺ ions increases by a factor of five, while the Tm³⁺ PL intensity at 1800 nm decreases by one order of magnitude. This phenomenon is attributed to a complicated energy transfer (ET) processes involving both Er³⁺ and Tm³⁺ and increase of phonon-assisted ET rate with temperature as well. It should be helpful to fully understand ET processes between Er and Tm and achieve flat and broad emission band at different operating temperatures.     

Infrared to visible upconversion fluorescence in Yb,Tm:YAG single crystal

Absorption spectrum from 400 to 2000 nm and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb³⁺ and 4 at.% Tm³⁺ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition ¹G₄ → ³H₆, the emission band around 646 nm corresponds to the transition ¹G₄ → ³F₄ of Tm³⁺. Energy transfer from Yb³⁺ to Tm³⁺ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of ¹G₄ level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions ¹G₄ → ³H₆ in YAG doped with Yb³⁺ and Tm³⁺ is potentially useful for blue light output.     

Spectral performance and intensive green upconversion luminescence in Er/Yb-codoped NaY(WO4)2 crystal

Using Czochralski (CZ) pulling method, an Er³⁺/Yb³⁺-codoped NaY(WO₄)₂ crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd-Ofelt (J-O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: ⁴G_11/2 + ⁴I_9/2 → ²H_11/2 (or ⁴S_3/2) + ²H_11/2 (or ⁴S_3/2), and ⁴G_11/2 + ⁴I_15/2 → ²H_11/2 (or ⁴S_3/2) + ²I_13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer ⁴G_11/2(Er³⁺) + ²F_7/2(Yb³⁺) → ⁴F_9/2(Er³⁺) + ²F_5/2(Yb³⁺) was also demonstrated.     

Structure dependence of near-infrared stimulated blue emission in polycrystalline Ln2(WO4)3 (Ln=Gd and Lu) doped with Tm and Yb

Tm- and Yb-doped gadolinium tungstate, (Gd_xTm_yYb_1−x−y)₂(WO₄)₃ (x=0.7-0.9; y=0.001-0.01), have been prepared by the polymerized complex method to achieve a homogeneous dispersion of dopants and to stabilize the host structure. Decomposition (900 °C 5 h) of the precursors with x=0.8-0.9 yielded a pure monoclinic phase, while that of x=0.7 resulted in formation of an orthorhombic impurity. The monoclinic phase exhibits bright up-converted blue emission due to the ¹G₄→³H₆ transition of Tm³⁺ (472 nm) upon excitation into the Yb³⁺:²F_7/2→²F_5/2 absorption band as a result of energy transfer from Yb to Tm. The orthorhombic impurity acts as a strong quencher of emission, and the quenching mechanism has been discussed on the basis of structural and spectroscopic properties of orthorhombic Lu₂(WO₄)₃:Tm,Yb prepared by the same method.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Green emission from Tb-doped SrSi2O2N2 phosphors under ultraviolet light irradiation

Tb-doped SrSi₂O₂N₂ phosphors with promising luminescent properties were synthesized by the conventional solid-state reaction method, characterized by powder X-ray diffraction and studied by photoluminescence excitation and emission spectra. The synthesized materials exhibited a weak blue emission and a strong green emission in the region of 400-470 nm and 480-650 nm, which are attributed to ⁵D₃→⁷F_j (j=5, 4, 3) and ⁵D₄→⁷F_j (j=6, 5, 4, 3) transitions of Tb³⁺, respectively. The green emission from ⁵D₄→⁷F₅ at 543 nm showed the highest intensity under the optimized concentration of 0.1 mol, after which the quenching concentration became relevant. The quenching behavior of the emission of Tb³⁺ was explained by the cross-relaxation of its excited state.     

Conversion of infrared radiation into visible emission in NaY(WO4)2:Yb, Ho crystal

The spectroscopic characteristics and fluorescence dynamics for Yb³⁺/Ho³⁺:NaY(WO₄)₂ crystal were investigated. The parameters of oscillator strengths, the spontaneous transition probabilities, the fluorescence branching ratios, the radiative lifetimes and the stimulated emission cross sections have been calculated based on Judd-Ofelt theory and Füchtbauer-Ladenburg method. The energy transfer efficiency from Yb³⁺ to Ho³⁺ was 65.85%. The green emission (530-570 nm) corresponding to (⁵F₄, ⁵S₂)→⁵I₈ transition, red emission (640-670 nm) due to ⁵F₅→⁵I₈ transition and NIR emission (740-770 nm) attributed to (⁵F₄, ⁵S₂)→⁵I₇ transition were observed on 974 nm excitation at room temperature. Under low pump power, the intensity of green light emission is weaker than that of the red light, while under high pump power, the case is on the contrary. The upconversion is based on the two-photon process either the energy transfer from Yb³⁺ ions or by the excited state absorption. The proposed mechanisms of upconversion emissions were provided.     

Optical absorption and emission properties of Nd in TeO2-WO3 and TeO2-WO3-CdO glasses

Effects of WO₃ and CdO on the spectroscopic properties of Nd³⁺ doped tellurite glasses were investigated. The optical band gaps and Urbach energies of the samples were determined using the dependence of the absorption coefficient on the photon energy. The Urbach energies were found to vary from 0.18 to 0.25 eV as the WO₃ content in the binary glasses decreased from 20.0 to 10.0 mol% while the optical band gap of the same glasses did not show an appreciable dependence on the glass composition. Judd-Ofelt (Ω_t) parameters were calculated from the optical absorption spectra measured at room temperature. In all the glasses the J-O parameters follow the same trend as Ω₂>Ω₆>Ω₄. The J-O intensity parameters were used to compute the radiative properties such as the radiative transition probabilities (A_ed), branching ratios (β) and radiative lifetimes (τ_r) for all the possible fluorescence bands. The fluorescence spectra obtained upon 805.2 nm excitation exhibited an intense emission band centered at 1064 nm (⁴F_3/2→⁴I_11/2) and two weak bands at 910 nm (⁴F_3/2→⁴I_9/2), and 1340 nm (⁴F_3/2→⁴I_13/2). The stimulated emission cross-section for the 1064 nm emission was determined using the emission spectra. The highest gain bandwidth (σ_e×Δλ_P) was determined to be 155.4 for the 0.79TeO₂-0.15WO₃-0.05CdO ternary glass composition, which could be more useful as promising material for the design and development of fiber amplifiers and lasers.     

Single color upconversion emission in Ho/Yb and Tm/Yb doped P2O5-MgO2-Sb2O3-MnO2-AgO glasses

The Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ doped P₂O₅-MgO₂-Sb₂O₃-MnO₂-AgO glasses were prepared by high temperature melting method. Under a 975 nm laser diode (LD) excitation, the single red and single blue upconversion (UC) emissions were observed in Ho³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ doped samples, respectively. By studying the spontaneous radiative and multiphonon relaxation probabilities, we find that the multiphonon relaxation probability of ⁵I₆ (Ho³⁺) state is very large (1.39 × 10⁶ s^− 1), which is helpful to the population of ⁵I₇ state. The multiphonon relaxation probability of ³H₅ and ³F_2,3 (Tm³⁺) is also very large, which results in lots of population in ³F₄ and ³H₄ states. The results are that the red UC emission of Ho³⁺ and the blue UC emission of Tm³⁺ are stronger.     

Synthesis, characterization and spectroscopic investigation of new tetrakis(acetylacetonato)thulate(III) complexes containing alkaline metals as countercations

In this work a series of tetrakis complexes C[Tm(acac)₄], where C⁺=Li⁺, Na⁺ and K⁺ countercations and acac=acetylacetonate ligand, were synthesized and characterized for photoluminescence investigation. The relevant aspect is that these complexes are water-free in the first coordination sphere. The emission spectra of the tetrakis Tm³⁺-complexes present narrow bands characteristic of the ¹G₄→³H₆ (479 nm), ¹G₄→³F₄ (650 nm) and ¹G₄→³H₅ (779 nm) transitions of the Tm³⁺ ion, with the blue emission color at 479 nm as the most prominent one. The lifetime values (τ) of the emitting ¹G₄ level of the C[Tm(acac)₄] complexes were 344, 360 and 400 ns for the Li⁺, Na⁺ and K⁺ countercations, respectively, showing an increasing linear behavior versus the ionic radius of the alkaline ion. An efficient intramolecular energy transfer process from the triplet state (T) of the ligands to the emitting ¹G₄ state of the Tm³⁺ ion is observed. This fact, together with the absence of water molecules in first coordination sphere, allows these tetrakis Tm³⁺-complexes to act as efficient blue light conversion molecular devices.     

Influence of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu2O3:2%Yb, 0.2%Tm nanopowders

Lutetium oxide nanopowders codoped with Tm³⁺ and Yb³⁺ were synthesized by the reverse-strike co-precipitation method. Effects of precipitant solution pH on the structural, morphological and upconversion luminescent properties of Lu₂O₃:2%Yb, 0.2%Tm nanopowders had been investigated. The results show that pH value of the precipitant (NH₄HCO₃) solution has a significant effect on the particle size, morphology and upconversion emission intensity of the Lu₂O₃:2%Yb, 0.2%Tm nanopowders. All the samples obtained from different pH value of precipitant solution can be readily indexed to pure cubic phase of Lu₂O₃, indicating good crystallinity. The upconversion emission intensity of Lu₂O₃:2%Yb, 0.2%Tm nanopowders obtained from the precipitant solution with pH=11 is the strongest. The enhancement of the upconversion luminescence is suggested to be the consequence of reducing the number of OH⁻ groups and the enlarged nanopowder size. The strong blue, weak red and near infrared emissions from the prepared nanopowders were observed under 980 nm laser excitation, and attributed to the ¹G₄→³H₆, ¹G₄→³F₄ and ³H₄→³H₆ transitions of Tm³⁺ ion, respectively.