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.     

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.     

Tuning size and up-conversion luminescence of CeO2:Yb3+/Er3+ nanoparticles through lanthanide doping

Particle size is a critical parameter in up-conversion luminescence tuning and application research. In this study, CeO₂:Yb³⁺/Er³⁺ nanospheres were synthesized via coprecipitation. The average size of these nanospheres gradually decreased as the Yb³⁺ doping concentration increased, which might be attributed to the influence of Yb³⁺ doping on the growth rate of nanospheres by surface charge repulsion. Upon exciting these nanospheres using a 980-nm laser, the corresponding up-conversion red-green emission intensity ratio gradually increased as the Yb³⁺ doping concentration increased, which might be ascribed to two reasons: the strengthened ⁴S_3/2 → ⁴F_9/2 nonradiative relaxation process and the enhanced Er³⁺ → Yb³⁺ energy back-transfer process. To assess the influence of the nonradiative relaxation process on the up-conversion emission red-green ratios, the down-conversion emission spectra and decay curves of CeO₂:x%Yb³⁺/2%Er³⁺ nanospheres that were excited by a 520 nm laser were investigated. To validate how the particle size affects the up-conversion emission, CeO₂:x%Lu³⁺/2%Yb³⁺/2%Er³⁺ nanospheres of various sizes were synthesized by substituting optically active Yb³⁺ using optically inert Lu³⁺. The corresponding up-conversion emission spectra and decay curves were investigated. The experimental results enhanced our understanding of how lanthanide doping affects the up-conversion luminescence tuning of Er³⁺, offering great potential to regulate the morphology and optical properties of the up-conversion luminescence nanoparticles.     

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.     

Electrospinning-derived YVO4:Er/Yb nanowires and nanotubes with temperature sensitivity of their up-converted emission

YVO₄:Er/Yb nanowires and nanotubes phosphors were prepared by electrospinning technique following calcination at different heating rates. The obtained nanowires are of 80–200 nm in diameter and are single crystals or polycrystalline in phase. The outer diameter of the obtained nanotubes is 50–200 nm with a wall thickness of 20–30 nm. The up-conversion properties of YVO₄:Er³⁺/Yb³⁺ nanowires and nanotubes were investigated. All samples were found to produce a green up-converted emission. The temperature-sensing features of YVO₄:Er³⁺/Yb³⁺ nanowires and nanotubes were investigated through the fluorescence intensity ratio approach, and the sensitivity of temperature was determined over the temperature range of 30–390 °C. The temperature sensing sensitivities of the mixed YVO₄:Er³⁺/Yb³⁺ nanowire samples and nanotubes exceeded the single YVO₄:Er³⁺/Yb³⁺ nanowire samples because of higher Yb³⁺-doped concentrations. The morphology influence on optical properties was studied at a fixed doping rare earth concentration and size. The temperature sensitivities of YVO₄:Er/Yb samples depended on the Yb ion concentrations rather than the morphology. The significant temperature sensitivity indicates its potential for use as an optical temperature sensing probe.     

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.     

Deep red upconversion photoluminescence in Er3+-doped Yb3Ga5O12 nanocrystalline garnet

The nanocrystalline single-phase Er³⁺-doped Yb₃Ga₅O₁₂ garnets have been prepared by the sol-gel combustion technique with a crystallite size of ≈30 nm. The presence of Yb³⁺ in garnet hosts allows their efficient excitation at the ≈977 nm wavelength. The Er³⁺ doping of Yb₃Ga₅O₁₂ garnet host results in deep red Er³⁺: ⁴F_9/2 → ⁴I_15/2 upconversion photoluminescence (UCPL) emission. The dominance of the red UCPL emission over the green Er³⁺: ⁴F_7/2/²H_11/2/⁴S_3/2 → ⁴I_15/2 component was investigated using the measurement of the steady-state and time-dependent Er³⁺ and Yb³⁺ emission spectra in combination with the power-dependent UCPL emission intensity. The proposed upconversion mechanism is discussed in terms of the Er³⁺ → Yb³⁺ energy back transfer process as well as Yb³⁺(Er³⁺) → Er³⁺ energy transfer and Er³⁺ ↔ Er³⁺ cross-relaxation processes. The studied Er³⁺-doped Yb₃Ga₅O₁₂ garnet may be utilized as a red upconversion emitting phosphor.     

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.     

Up-conversion luminescence and optical thermometry properties of transparent glass ceramics containing CaF2:Yb3+/Er3+ nanocrystals

A series of Yb³⁺/Er³⁺ codoped transparent oxyfluoride glass ceramics with various amounts of Yb³⁺ have been successfully fabricated and characterized. Under 980 nm laser prompting, the samples produce intense red, green and blue up-conversion emissions, and the emission intensities increase with Yb³⁺ concentration and heat treatment temperature. Before losing good transparency in the visible region, optimum emission intensities are obtained for the sample with 25 mol% of Yb³⁺ at a heat treatment temperature of 680 °C. A possible up-conversion mechanism is proposed from the dependence of emission intensities on pumping power. The fluorescence intensity ratio between the two thermally coupled levels ²H_11/2 versus ⁴S_3/2 was measured with the laser output power of 57 mW to avoid the possible laser induced heating effect. The fluorescence intensity ratio values in the temperature range from 295 K to 723 K can be well fitted with the equation: A exp (−∆E/k_BT), where A = 6.79 and ∆E=876 cm⁻¹. The relative temperature sensitivity at 300 K was evaluated to be 1.4% K⁻¹. All the results suggest that the Yb³⁺/Er³⁺ codoped CaF₂ glass ceramics is an efficient up-conversion material with potential in optical fiber temperature sensing.     

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.     

Visible up-conversion luminescence of CaWO<Subscript>4</Subscript>: Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> and emission enhancement by tri-doping of Li<Superscript>+</Superscript> ions

Er³⁺,Yb³⁺ co-doped CaWO₄ polycrystalline powders were prepared by a solid-state reaction and their up-conversion (UC) luminescence properties were investigated in detail. Under 980 nm laser excitation, CaWO₄: Er³⁺,Yb³⁺ powder exhibited green UC emission peaks at 530 and 550 nm, which were due to the transitions of Er³⁺ (²H_11/2)→Er³⁺ (⁴I_15/2) and Er³⁺ (⁴S_3/2)→Er³⁺ (⁴I_15/2), respectively. Effects of Li+ tri-doping into CaWO₄: Er³⁺,Yb³⁺ were investigated. The introduction of Li⁺ ions reduced the optimum calcinations temperature about 100 °C by a liquid-phase sintering process and the UC emission intensity was remarkably enhanced by Li⁺ ions, which could be attributed to the lowering of the symmetry of the crystal field around Er³⁺ ions.     

Microwave Sol–Gel Synthesis of CaGd2(MoO4)4:Er3+/Yb3+ Phosphors and Their Upconversion Photoluminescence Properties

CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ phosphors with the doping concentrations of Er³⁺ and Yb³⁺ (x = Er³⁺ + Yb³⁺, Er³⁺ = 0.05, 0.1, 0.2, and Yb³⁺ = 0.2, 0.45) have been successfully synthesized by the microwave sol–gel method, and the crystal structure refinement and upconversion photoluminescence properties have been investigated. The synthesized particles, being formed after heat‐treatment at 900°C for 16 h, showed a well‐crystallized morphology. Under the excitation at 980 nm, CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ particles exhibited strong 525 and 550‐nm emission bands in the green region and a weak 655‐nm emission band in the red region. The Raman spectrum of undoped CaGd₂(MoO₄)₄ revealed about 15 narrow lines. The strongest band observed at 903 cm^?1 was assigned to the ν₁ symmetric stretching vibration of MoO₄ tetrahedrons. The spectra of the samples doped with Er and Yb obtained under 514.5 nm excitation were dominated by Er³⁺ luminescence preventing the recording Raman spectra of these samples. Concentration quenching of the erbium luminescence at ²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions in the CaGd₂(MoO₄)₄:Er³⁺/Yb³⁺ crystal structure was established to be approximately at the 10 at.% doping level.     

Lower power dependent upconversion multicolor tunable properties in TiO2:Yb3+/Er3+/ (Tm3+)

Multicolor tunable upconversion luminescence materials could be applied to polychromatic LED and anti-counterfeit due to their superiority in abundant color and security feature. However, the harsh terms to achieve emission tuning associated with the drawbacks, including changing the concentration or types of doping ions, higher temperature, and higher excitation power, limit the range of its application. In this paper, a convenient and versatile approach for multicolor-emitting is realized via simply lower power modulating in TiO₂:Yb³⁺/ Er³⁺ and TiO₂: Yb³⁺/Er³⁺/Tm³⁺. The emission color is tuned from pink to yellowish green in TiO₂:Yb³⁺/ Er³⁺ and tuned from white to yellowish green in TiO₂: Yb³⁺/Er³⁺/Tm³⁺. It's found that there is no apparent temperature variation at lower power. Meanwhile, the mechanism of the emission and the multicolor tunability is discussed.     

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     

Transmission electron microscopic and optical spectroscopic studies of Ni2+/Yb3+/Er3+/Tm3+ doped dual‐phase glass‐ceramics

Ni²⁺/Yb³⁺/Er³⁺/Tm³⁺ codoped transparent glass‐ceramics (GCs) containing both hexagonal β‐YF₃ and spinel‐like γ‐Ga₂O₃ dual‐phase nanoparticles (NCs) are synthesized by melt‐quenching and subsequent heating procedures. Two techniques of transmission electron microscopy (TEM) nanoanalytics and optical spectroscopy are conjugated to understand the distribution of the rare‐earth ions (REs) and transition metals (TMs) in the nanostructured GCs. It is found that the REs are located predominantly in β‐YF₃, whereas the TMs in γ‐Ga₂O₃ NCs. As a result, energy transfer (ET) between the REs and TMs is considerably suppressed due to the large spatial separation (> 3 nm), but it is enhanced between the REs partitioned in the β‐YF₃ NCs. This has important implications for intended and demanding photoluminescence functions. For example, an ultrabroadband near‐infrared (NIR) emission in the wavelength region of 1000‐2000 nm covering the entire telecommunications window is observed for the first time. Meanwhile, intense upconversion (UC) emissions covering the 3 primary colors and locating in the first biological window can be also recorded under excitation by a single pump source at 980 nm.     

Effect of crystalline fraction on upconversion luminescence in Er3+/Yb3+ Co-doped NaYF4 oxyfluoride glass-ceramics

The crystalline fraction were adjusted MgO concentration and the corresponding effect on upconversion (UC) luminescence in Er³⁺/Yb³⁺ co-doped NaYF₄ oxyfluorode glass-ceramics was investigated. With increase of MgO and the content of Na₂O reduced, the internal network structure of the glass became compact, which made the size of NaYF₄ nanocrystals unchanged, while the average distance between the nanocrystals increased significantly. Crystal growth is limited with the glass network, keeping the crystal size not changed. SNM-1 glass ceramics samples show a predominant red up-conversion emission under near infrared excitation at 980 nm, while a predominant green emission is observed in the SNM-3 samples. In this paper, it was indicated that it changed the effect of glass network modifier MgO in the glass structure. The possible mechanism responsible for the color variation of UC in Er³⁺/Yb³⁺ co-doped was discussed.     

Spectroscopic analysis of up conversion luminescence in doped halogeno-antimonite glass

The up-conversion emission of Nd³⁺, Sm³⁺ and Er³⁺ has been studied in a new halogeno-antimonite glass with the chemical composition 80 Sb₂O₃ – 10 ZnBr₂ – 10 KCl. Doping concentration was 0.2?mol% of lanthanide (Ln) ions. Rare earths were introduced as fluorides LnF₃ that were further converted into oxides. Main physical properties of base glass were measured, including density, thermal expansion, characteristic temperatures, refractive index and optical transmission. The amount of residual hydroxyls was calculated from the OH absorption band around 3000?nm. The recorded up-conversion emission lines are λ_em =?536?nm for Nd³⁺ pumped at 805?nm; λ_em =?563?nm, 600?nm, 631?nm and 645?nm for Sm³⁺ pumped at 945?nm; λ_em =?531?nm for Er³⁺ pumped at 798?nm. Co-doped glass (0.1 Yb³⁺ + 0.1 Er³⁺) pumped at 980?nm has three emission lines at 524?nm, 545?nm and 650?nm. Corresponding transitions have been identified and the mechanisms ruling the up-conversion process is discussed. They include excited state absorption (ESA), energy transfer (ET) cooperative energy transfer (CET), emission assisted by phonon (EAP), multiphonon relaxation (MR) and cross- relaxation (CR).     

Design and preparation of white light emission from up-conversion transitions in Er3+/Tm3+/Yb3+ co-doped cubic zirconia single crystals

High-quality cubic YSZ crystals were designed with various contents of Er³⁺, Tm³⁺ and Yb³⁺ to produce white light emission, and grown by the optical floating zone method. The up-conversion luminescence spectra of the crystals under 980 nm laser irradiation show three distinct groups of emission peaks at ∼473 nm (blue) generated by the Tm^{3+ 1}G₄→³H₆ transition, 531 and 547 nm (green) from the Er^{3+ 2}H_11/2 → ⁴I_15/2 and ⁴S_3/2 → ⁴I_15/2 transitions, and 640 and 662 nm (red) from the Er^{3+ 4}F_9/2 → ⁴I_15/2 transition. The optical power curve obtained by plotting the up-conversion luminescence intensity against the laser power shows that the blue emission involves a three-photon process, whilst both the green and red emissions are the results of two-photon processes. Overall white light emission was observed with the crystal prepared with 0.05 mol% Er₂O₃, 0.5 mol% Tm₂O₃ and 2.0 mol% Yb₂O₃, and this crystal is suitable for use in highly efficient white light emission devices.     

Influence of Cr3+ on yellowish-green UC emission and energy transfer of Er3+/Cr3+/Yb3+ tri-doped zinc silicate glasses

In this paper, we study the influence of Cr³⁺ on yellowish-green upconversion (UC) emission and the energy transfer (ET) of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ (SZNL) zinc silicate glasses under excitation of the 980 nm laser diode (LD). The influence of Cr³⁺ on enhancing the red UC emission of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses under the excitation of 980nm LD was also investigated. The ET processes between Yb³⁺, Cr^3+, and Er³⁺, together with the combination of Yb³⁺-Cr³⁺-Er³⁺, which led to the green UC emission intensity of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in SiO₂–ZnO–Na₂O–La₂O₃ zinc silicate glasses bands centered at ~546 nm have been significantly enhanced. By increasing the concentration of Cr³⁺ from 0 up to 5 mol.%, we can locate the Commission Internationale de l'éclairage (CIE) 1931 (x; y) chromaticity coordinates for UC emissions of Er³⁺/Cr³⁺/Yb³⁺ tri-doped in the central position of the yellowish-green color region of CIE 1931 chromaticity diagram. Besides, the ET processes between the Yb³⁺, Cr³⁺, and Er³⁺ are also proposed and discussed.