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.     

Enhanced green upconversion luminescence properties of Er3+/Yb3+ co-doped strontium gadolinium silicate oxyapatite phosphor

Upconversion Sr₂(Gd_.98-xEr_.02Yb_x)₈Si₆O₂₆ (SGSO:2Er³⁺/xYb³⁺) phosphor materials were synthesized using a citrate sol-gel process. X-ray diffraction patterns confirmed their hexagonal structure. Field emission scanning electron microscopy images of SGSO:2Er³⁺/xYb³⁺ phosphors depicted submicron particles. The enhanced upconversion luminescence properties of SGSO:2Er³⁺/xYb³⁺ phosphors were analysed as a function of Yb³⁺ ion concentration and laser power. The energy transfer induced enhanced emission of the Er³⁺/ Yb³⁺ ions co-doped SGSO phosphors was ascribed to multi-phonon relaxation. The calculated chromaticity coordinates of the SGSO:2Er³⁺/xYb³⁺ phosphors showed emissions could be tuned by changing Yb³⁺ ion concentration. Optimized sample exhibited the chromaticity coordinate values near to the ultra-high definition television standard green emission coordinates.     

Color tunable up-conversion emission of ZrO2:Yb3+, Er3+ thin films prepared by chemical solution deposition

The color-tunable up-conversion (UC) emission was observed in ZrO₂:Yb³⁺, Er³⁺ thin films synthesized on fused silica substrates using a chemical solution deposition method. The crystal structure, surface morphology image and optical transmittance of ZrO₂:Yb³⁺, Er³⁺ thin films were detected in the matter of Yb³⁺/Er³⁺ doping content. Under excitation by 980?nm infrared light, intense UC emission can be obtained from ZrO₂:Yb³⁺, Er³⁺ thin films. Photoluminescence study shows that there are two emission bands centered at 548?nm and 660?nm in the UC luminescence spectra, which can be owing to (²H_11/2,⁴S_3/2)→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺ ions, respectively. In addition, the color coordinate of UC emission between green-red can be tuned by properly adjusting the dopant concentration, because the composition of Yb³⁺/Er³⁺ affect the red/green ratio via the process of cross relaxation and energy back transfer. Our study suggests that ZrO₂:Yb³⁺, Er³⁺ thin films can be considered as promising materials for new photoluminescence devices.     

Color-tunable up-conversion luminescence of Zn(AlxGa1-x)2O4:Yb3+,Tm3+,Er3+ powders

Color-tunable up-conversion powder phosphors Zn(Al_xGa_1-x)₂O₄: Yb³⁺,Tm³⁺,Er³⁺ were synthesized via high temperature solid-state reaction. Also, the morphological and structural characterization, up-conversion luminescent properties were all investigated in this paper. In brief, under the excitation of a 980?nm laser, all powders have same emission peaks containing blue emission at 477?nm (attributed to ¹G₄→³H₆ transition of Tm³⁺ ions), green emission at 526?nm and 549?nm (attributed to ²H_11/2→ ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions respectively), red emission at about 659?nm and 694?nm (attributed to ⁴F_9/2→⁴I_15/2 transition of Er³⁺ ions and ³F₃→³H₆ transition of Tm³⁺ ions, respectively), which are not changed after the doping of Al³⁺ ions. However, the doping of Al³⁺ ions can enhance the up-conversion luminescent intensity and efficiency, while the emission color of as-prepared powder phosphors can be tunable by controlling the doping amount of Al³⁺ ions. Taking Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er as the cut-off value, the emissions have clear blue-shift firstly and then show obvious red-shift with the increasing doping of Al³⁺ ions. Stated thus, pink emission in ZnAl₂O₄:Yb,Tm,Er, purplish pink emission in ZnGa₂O₄:Yb,Tm,Er and Zn(Al_0.9Ga_0.1)₂O₄:Yb,Tm,Er, purple emission in Zn(Al_0.1Ga_0.9)₂O₄:Yb,Tm,Er and Zn(Al_0.3Ga_0.7)₂O₄:Yb,Tm,Er, purplish blue emission in Zn(Al_0.7Ga_0.3)₂O₄:Yb,Tm,Er, blue emission in Zn(Al_0.5Ga_0.5)₂O₄:Yb,Tm,Er can be observed, which confirm the potential applications of as-prepared Zn(Al_xGa_1-x)₂O₄:Yb³⁺,Tm³⁺,Er³⁺ powder phosphors in luminous paint, infrared detection and so on.     

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.     

Triple NIR light excited up-conversion luminescence in lanthanide-doped BaTiO3 phosphors for anti-counterfeiting

Up-conversion luminescent (UCL) materials are excellent candidate for optical anti-counterfeiting and the exploitation of multi-wavelength NIR light triggered UC phosphors with tunable color emission is essential for reliable anti-counterfeiting technology. Herein, a series of lanthanide ions (Er³⁺, Er³⁺–Ho³⁺, and Yb³⁺–Tm³⁺) doped BaTiO₃ submicrometer particles are synthesized through a modified hydrothermal procedure. XRD and SEM measurements were carried out to identify the structure and morphology of the samples and their UCL properties under 808, 980, and 1550 nm NIR excitation are investigated. Er³⁺ singly doped sample exhibits Er³⁺ concentration-dependent and excitation wavelength-dependent emission color from green to yellow and orange. The corresponding UC mechanisms under three NIR light excitation are clarified. Pure red emission under 1550-nm excitation was obtained by introducing small amount of Ho³⁺ and the fluorescent lifetime test was used to confirm the energy transfer from Er³⁺ to Ho³⁺. In addition, Yb³⁺–Tm³⁺ co-doped sample shows intense blue emission from ¹G₄ → ³H₆ transition of Tm³⁺ under 980-nm excitation. As a proof of concept, the designed pattern using phosphors with red, green, and blue three primary color emissions under 1550, 808, and 980 nm NIR excitation was displayed to demonstrate their anti-counterfeiting application.     

Optimization of sensitizer concentration for upconversion photoluminescence of Yb3+/Er3+: La10W22O81 nanophosphor rods

Yb³⁺/Er³⁺codoped La₁₀W₂₂O₈₁ (LWO) nanophosphor rods have been successfully synthesized by a facile hydrothermal assisted solid state reaction method, and their upconversion photoluminescence properties were systematically studied. X-ray diffraction patterns revealed that the nanophosphors have an orthorhombic structure with space group Pbcn (60). A microflowers-like morphology with irregular hexagonal nanorods was observed using field emission scanning electron microscopy for the Yb³⁺(2 mol%)/Er³⁺(2 mol%):LWO nanophosphor. The shape and size of the nanophosphor and the elements along with their ionic states in the material were confirmed by TEM and XPS studies, respectively. A green upconversion emission was observed in the Er³⁺: LWO nanophosphors under 980 nm laser excitation. A significant improvement in upconversion emission has been observed in the Er³⁺: LWO nanophosphors by increasing the Er³⁺ ion concentration. A decrease in the upconversion emission occurred due to concentration quenching when the doping concentration of Er³⁺ ions was greater than 2 mol%. An optimized Er³⁺(2 mol%): LWO nanophosphor exhibited a strong near infrared emission at 1.53 μm by 980 nm excitation. The green upconversion emission of Er³⁺(2 mol%): LWO was remarkably enhanced by co-doping with Yb³⁺ ions under 980 nm excitation because of energy transfer from Yb³⁺ to Er³⁺. The naked eye observed this upconversion emission when co-doping with 2 mol% Yb³⁺. In order to obtain the high upconversion green emission, the optimized sensitizer concentration of Yb³⁺ ions was found to be 2 mol%. The upconversion emission trends were studied as a function of stimulating laser power for an optimized sample. Moreover, the NIR emission intensity has also been enhanced by co-doping with Yb³⁺ ions due to energy transfer from Yb³⁺ to Er³⁺. The energy transfer dynamics were systematically elucidated by energy level scheme. Colorimetric coordinates were determined for Er³⁺ and Yb³⁺/Er³⁺: LWO nanophosphors. The energy transfer mechanism was well explained and substantiated by several fluorescence dynamics of upconversion emission spectra and CIE coordinates. The results demonstrated that the co-doped Yb³⁺(2 mol%)/Er³⁺(2 mol%): LWO nanophosphor material is found to be a suitable candidate for the novel upconversion photonic devices.     

Color-tunable up-conversion emission in Y2O3:Yb3+, Er3+ nanoparticles prepared by polymer complex solution method

Abstract

Powders of Y₂O₃ co-doped with Yb³⁺ and Er³⁺ composed of well-crystallized nanoparticles (30 to 50 nm in diameter) with no adsorbed ligand species on their surface are prepared by polymer complex solution method. These powders exhibit up-conversion emission upon 978-nm excitation with a color that can be tuned from green to red by changing the Yb³⁺/Er³⁺ concentration ratio. The mechanism underlying up-conversion color changes is presented along with material structural and optical properties.

PACS

42.70.-a, 78.55.Hx, 78.60.-b     

Bright red upconversion luminescence from Er3+ and Yb3+ co-doped ZnO-TiO2 composite phosphor powder

ZnO-TiO₂ composites co-doped with Er³⁺ and Yb³⁺ ions were successfully synthesized by powder-solution mixing method and their upconversion (UC) luminescence was evaluated. The effect of firing temperature, ZnO/TiO₂ mixing ratio, and dopant concentration ranges on structural and UC luminescence properties was investigated. The crystal structure of the product was studied and calculated in detail by means of X-ray diffraction (XRD). Also, the site preference of Er³⁺ and Yb³⁺ ions in the host material was considered and analyzed based on XRD results and UC luminescence characteristics. Brightest UC luminescence was observed in the ZnO-TiO₂:Er³⁺,Yb³⁺ phosphor fired at 1300 °C in which the system consisted of mixed phases; Zn₂TiO₄, TiO₂, RE₂Ti₂O₇ and RE₂TiO₅ (RE = Er³⁺ and/or Yb³⁺). Under the excitation of a 980 nm laser, the two emission bands were detected in the UC emission spectrum, weak green band centered at 544 and 559 nm, and strong red band centered at 657 and 675 nm wavelengths in accordance with ²H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ ion, respectively. The simple chemical formula equations, for explaining the site preference of Er³⁺ and Yb³⁺ ions in host crystal matrix, were generated by considering the Zn₂TiO₄ crystal structure, its crystal properties, and the effect of Er³⁺ and Yb³⁺ ions to the host crystal matrix. The UC emission intensity of the products was changed by varying ZnO/TiO₂ mixing ratios, and Er³⁺ and Yb³⁺ concentrations. The best suitable condition for emitting the brightest UC emission was 1ZnO:1TiO₂ doped with 3 mol% Er³⁺, 9 mol% Yb³⁺ fired at 1300 °C for 1 h.     

Enhanced upconversion study of Er3+-Yb3+ codoped NaYF4 phosphors synthesized by the reverse microemulsion method

Herein, nanocrystals of Er³⁺ and Er³⁺, Yb³⁺ co-doped NaYF₄ upconversion (UC) phosphor were prepared via the reverse-microemulsion method. The impact of different concentrations of Er³⁺ ions on the UC emission intensity after 980?nm diode laser excitation is discussed. The structure, morphology and composition of the nanophosphors were confirmed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and the results showed the presence of NaYF₄ nanocrystals with hexagonal phases of NaYF₄. The UC spectra revealed two emission bands including a green and a red emission band and the CIE coordinate for the samples were estimated. The present research revealed that the reverse-microemulsion approach will be suitable for the synthesis of efficient upconversion nanophosphors.     

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.     

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.     

Effect of silica coating on the structural and luminescent properties of Sm3+/Yb3+ or Tm3+/Yb3+ co-doped TiO2 nanoparticles

The luminescent characteristics of spherical titanium dioxide (TiO₂) nanoparticles (NP's) doped with Sm³⁺/Yb³⁺ and Tm³⁺/Yb³⁺ with and without a silica coating were analyzed. These nanoparticles were synthesized using the spray pyrolysis technique and coated with silica through a wet chemical process. The Sm³⁺/Tm³⁺ and Yb³⁺ doping induces a triphasic poly-crystalline structure of rutile and anatase TiO₂ and a Sm₂Ti₂O₇/Tm₂Ti₂O₇ cubic phase. A Williamson-Hall analysis was used to monitor the tensions of the NP's crystallites at the various doping concentrations and with addition of the silica shell. The luminescent spectra presented the characteristic emission peaks for the electronic energy levels transitions of the Sm³⁺/Tm³⁺ and Yb³⁺ ions. The Sm³⁺/Yb³⁺ co-doped NP's showed a maximum emission peak in the visible region at 612 nm, associated with ⁴G_5/2 → ⁶H_7/2 transitions of the Sm³⁺ ions. The IR emission peak at 973 nm (²F_5/2 → ²F_7/2) pertaining to Yb³⁺. For the combination of Tm³⁺/Yb³⁺, two emissions associated with Tm³⁺ ions were observed at 440 nm (¹D₂ → ³F₄) and 806 nm (³H₄ → ³H₆). The emission at 973 nm (²F_5/2 → ²F_7/2) is correlated to the Yb³⁺ ions. Silica coating of the NP's resulted in luminescence emission intensity increase of about 4 times.     

A Novel Multifunctional Upconversion Phosphor: Yb3+/Er3+ Codoped La2S3

Yb³⁺/Er³⁺ codoped La₂S₃ upconversion (UC) phosphors have been synthesized using high‐temperature solid‐state method. Under 971‐nm excitation, the maximum luminescence power can reach 0.64 mW at the excitation power density of 16 W/cm² and an absolute power yield of 0.36% was determined by an absolute method at the excitation power density of 3 W/cm², and the quantum yield of La₂S₃:Yb³⁺, Er³⁺ (green ~0.18%, red ~0.03%, integration ~0.21) was comparable to that of NaYF₄:Yb³⁺, Er³⁺ nanocrystals (integration ~0.005–0.30). Frequency upconverted emissions from two thermally coupled excited states of Er³⁺ were recorded in the temperature range 100–900 K. The maximum sensitivity of temperature sensing is 0.0075 K^?1. As the excitation power density increases, the temperature of host materials rapidly rises and the top temperature can reach to 600 K. Given the intense UC emission, high sensitivity, as well as good photothermal stability, La₂S₃:Yb³⁺/Er³⁺ phosphor can become a promising composite material for photothermal ablation of cancer cells possessing the functions of temperature sensing and in vivo imaging.     

Highly Sensitive Optical Thermometry of Yb3+‐Er3+ Codoped AgLa(MoO4)2 Green Upconversion Phosphor

Er³⁺–Yb³⁺ codoped AgLa(MoO₄)₂ phosphors with intense green emission from ²H_11/2/⁴S_3/2 → ⁴I_15/2 transitions and negligible red emission from ⁴F_9/2 → ⁴I_15/2 transition of Er³⁺ were synthesized by sol–gel process. Its temperature sensing performance was evaluated based on the temperature dependence of fluorescence intensity ratio (FIR) of two green emission bands in the range 300–510 K. The maximum sensitivity of AgLa(MoO₄)₂: 0.02Er³⁺/0.4Yb³⁺ is approximately 0.018 K^?1 at 480 K, which is much higher than those of reported samples based on green emissions of Er³⁺. Result suggests that AgLa(MoO₄)₂: Er³⁺/Yb³⁺ has a great potential application in optical temperature sensors.     

Yb3+ concentration on emission color,thermal sensing and optical heater behavior of Er3+ doped Y6O5F8 phosphor

Up-conversion phosphor is a potential candidate as non-contact temperature sensor because of its unjammable and unique detection abilities. In this work, we investigate the influence of Yb³⁺ concentration on the emission color, thermal sensing and optical heater behavior of Er³⁺ doped Y₆O₅F₈ phosphor. Our results show that the emission color of Er³⁺ and Yb³⁺ co-doped Y₆O₅F₈ powder changes from green to yellow with the Yb³⁺ concentration increasing. Importantly, the temperature sensing sensitivities of Er³⁺ and Yb³⁺ co-doped Y₆O₅F₈ powder reach 0.008, 0.009, 0.010 and 0.011 K⁻¹ as the sample doped with 2%, 5%, 8% and 11% Yb³⁺ at 476 K, respectively. Moreover, the temperature of high Yb³⁺ concentration sample shows preferable optical heating behavior, whose temperature is ascended by a large value of 94 K when the excitation pump power density changes from 1.0 to 13.1 W cm⁻². These results suggest Er³⁺ and Yb³⁺ co-doped Y₆O₅F₈ powder has great potential in colorful display, temperature sensing and optical heating.     

Near/mid‐infrared emission and energy transfer of Er/Tm‐Yb co‐doped β‐NaYF4 microcrystals

The well‐formed high quality β‐NaYF₄:Er³⁺/Tm³⁺, Yb³⁺ microcrystals with near/mid‐infrared (NIR/MIR) emission are synthesized by the solvothermal method. Obvious 1.4 μm, 1.8 μm emissions, and 1.5 μm emission are observed in as‐prepared β‐NaYF₄:Tm³⁺, Yb³⁺ and β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals, respectively. To obtain MIR emission, the as‐prepared β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals are heat‐treated at different temperature schedule and atmosphere, it demonstrates there is great effect on the morphology and crystal structure when heat‐treated at different temperature, while little effect under different heat‐treated atmosphere. Subsequently, after heat‐treatment at 575°C in air, owing to the efficient elimination of internal defects and partly surface hydroxyl/citrate groups, an obvious 2.7 μm MIR emission is successfully detected in heat‐treated β‐NaYF₄:Er³⁺, Yb³⁺ microcrystals for the first time.     

Optical properties of Er3+/Yb3+ co-doped phosphate glass system for NIR lasers and fiber amplifiers

In this research, the optical properties of Er³⁺/Yb³⁺ co-doped phosphate glass have been studied to explore the potential of this glass system in laser and electronic amplifiers. The Judd–Ofelt (J-O) intensity parameter (Ω_t) in the J-O model was established to determine the absorption intensity of the glass. The optical properties of the glass can be evaluated by various radiation parameters such as the radiative transition probabilities (A_rad), stimulated emission cross sections (σ_e), branching ratios (β_JJ'), maximum half-width values (Δλ_p), and the radiation lifetime (τ_rad) of the glass. It was found that in the case of Yb³⁺ as a sensitizer, the spectral properties of the Er³⁺ doped glass can be maximized. The data of A_rad, β_JJ', τ_rad, σ_e and Δλ_p obtained by Er³⁺/Yb³⁺ co-doping can find that the Er³⁺-doped sample undergoes ⁴I_13/2–⁴I_15/2 transition at 1.56?µm, and the stimulated emission cross section is greatly improved. The application prospects of the glass in solid near-infrared laser and electronic communication was discussed. According to the comprehensive discussion and analysis, the glass has great application potential.     

Enhancement of up-conversion emission and emerging cool white light emission in co-doped Yb3+/ Er3+: Li2O-LiF-B2O3-ZnO glasses for photonic applications

A series of co-doped (Yb³⁺/Er³⁺): Li₂O-LiF-B₂O₃-ZnO glasses were prepared by standard melt quenching technique. Structural and morphological studies were carried out by XRD and FESEM. Phonon energy dynamics have been clearly elucidated by Laser Raman analysis. The pertinent absorption bands were observed in optical absorption spectra of singly doped and co-doped Yb³⁺/Er³⁺: LBZ glasses. We have been observed a strong up-conversion red emission pertaining to Er³⁺ ions at 1.0 mol% under the excitation of 980 nm. However, the up-conversion and down conversion (1.53 µm) emission intensities were remarkably enhanced with the addition of Yb³⁺ ions to Er³⁺: LBZ glasses due to energy transfer from Yb³⁺ to Er³⁺. Up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses exhibits three strong emissions at 480 nm, 541 nm and 610 nm which are assigned with corresponding electronic transitions of ²H_9/2 → ⁴I_15/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 respectively. Consequently, the green to red ratio values (G/R) also supports the strong up-conversion emission. The Commission International de E′clairage coordinates and correlated color temperatures (CCT) were calculated from their up-conversion emission spectra of co-doped (Yb³⁺/Er³⁺): LBZ glasses. The obtained chromaticity coordinates for optimized glass (0.332, 0.337) with CCT value at 5520 K are very close to the standard white colorimetric point in cool white region. These results could be suggested that the obtained co-doped (Yb³⁺/Er³⁺): LBZ glasses are promising candidates for w-LEDs applications.     

Upconversion emission of ZrO2 nanoparticles doped with erbium (Er3+) and ytterbium (Yb3+), synthesized by hydrothermal route

This paper reports the luminescent response upconversion of zirconium oxide (ZrO₂) nanoparticles doped with erbium (Er³⁺) and ytterbium (Yb³⁺) ions, synthesized by hydrothermal route. X ray diffraction (DRX) showed that the synthesized material presents the face centered cubic (FCC) structure. High resolution transmission electron microscopy (HRTEM) showed the presence of crystals size smaller than 10 nm. The photoluminescent analysis allowed to observe an intense upconversion luminescence emission of the samples doped with both ions Er³⁺ and Yb³⁺, when these are excited with 910 nm laser source, showing the electronic transitions ⁴F_9/2 → ⁴I_5/2; ²H_11/2 → ⁴I_5/2; ⁴S_3/2 → ⁴I_15/2 of Er³⁺. Two decay times were observed, whose behavior can be associated to the average distance between erbium ions within the nanocrystals.