Na5Lu9F32 Single Crystals Research Articles

Enhanced Red Emission of Na5Lu9F32: Eu3+ Single Crystal by Introducing of GdF3

AbstractThe bulk Na5Lu9F32 single crystals with high quality serial Eu3+/Gd3+ co‐doped were grown by an ameliorative Bridgman technique. The measurement of X‐ray diffraction (XRD) and analysis of Rietveld refinement were implemented to validate the crystal phase. The Eu3+ doped Na5Lu9F32 single crystal emits intense red emission at 611 nm excited by 394 nm light. The intensity of 1.8 mol % Gd3+ doped sample is boosted by 3.56 times compared with the un‐doped one. The doping of Gd3+ ions replace competitively Lu3+ lattice sites with Eu3+ ions. Thus, they cause the lattice distortion and reduction of symmetry, enabling Eu3+ ions to overcome their 4f forbidden transitions. The change of Eu3+ ion local environment induced by Gd3+ ion doping was explored by the Eu3+ emission spectra and the variations of ratios between red and orange emission intensities (R/O). The fluorescence lifetime indicates that the introduction of GdF3 decreases the probability of non‐radiative transitions and increases the fluorescence lifetime. These results demonstrated that the Na5Lu9F32: Eu3+ single crystal doped with an appropriate concentration of GdF3 is a type of promising red emission single crystal for related optical devices of detector and laser due to its strong red emission, high transparency and high physico‐chemical stability.

Enhanced the yellow emission of Dy3+/Eu3+: Na5Lu9F32 fluoride single crystals by the introduction of inactive central Y3+ ions

High-quality Na5Lu9F32 single crystals incorporated with Dy3+, Dy3+/Eu3+, and Dy3+/Eu3+/Y3+ ions were successfully synthesized by a reformative Bridgman technique. A significantly enhanced 573nm yellow emission for the Dy3+/Eu3+ incorporated crystal by dopant of inactive central Y3+ ions was demonstrated upon excitation of 453nm. The broken of the Dy3+ clusters by addition of Y3+ dopant was probably the main reason for the enhancement of the yellow emission. The crystal still held the phase of Na5Lu9F32 although the doping level reaches to 1.5 mol% Y3+ while the peaks of X-ray diffraction (XRD) were slightly blue-shifted, and Y3+ ions replaced the Lu3+ lattices as consequence of Rietveld structure refinements of the crystals. The maximum excited absorption and emission cross-sections at 573nm were also computed to be ∼8.91×10−21 and ∼6.06×10−21 cm2 separately. Therefore, the Dy3+/Eu3+/Y3+ tri-doped Na5Lu9F32 single crystal was considered as a prospective yellow solid-state laser material for related optical devices.

Enhanced orange-red emission in Eu3+/Li+ co-doped Na5Lu9F32 fluoride single crystal upon excitation of 394 nm

In this study, a series of transparent 0.5 Eu3+/χ Li+ (χ = 0, 0.3, 0.6, 0.9, and 1.2): Na5Lu9F32 fluoride single crystals with high-quality were successfully grown by a modified Bridgman technique. The impacts of Li+ ion dopant on the luminous properties of Na5Lu9F32 doped Eu3+ single crystals were studied by fluorescence spectra, decay curves and absorption spectra. The doping of Li+ was beneficial for improvement of the orange-red emission, and the emission intensity of Eu3+ singly doped crystal could be doubled by co-doping 0.9 mol% Li+ ions. The variations of local environment around the Eu3+ ions after Li+ ions doping were probed by the emission spectra and the changes of ratios between red and orange emission intensities (R/O). Additionally, internal quantum efficiency of Eu3+/Li+: Na5Lu9F32 single crystal could be reached to ∼18.25%. Therefore, Eu3+/Li+: Na5Lu9F32 single crystal was considered as a potential material for orange-red laser and related optical devices.

Enhanced ∼2.85 μm mid-infrared emission of Na5Lu9F32: Pr3+/Ho3+ single crystal by introducing of non active Gd3+ ions

A series of novel Na5Lu9F32 fluoride single crystals by keeping the concentrations of Ho3+ (0.5 mol%) and Pr3+ (0.1 mol%) fixed and varying the concentrations of Gd3+ ions (i.e., 0, 0.5, 1.0, 1.2, 1.5 mol%) were prepared successfully by a reformative Bridgman technique for application of 2.85 μm mid-infrared. The impact of the non active Gd3+ ion on the crystallographic structure and optical properties of the single crystal were explored by the aid of the X-ray diffraction, Rietveld refinement, spectra of absorption and emission and decay curves of fluorescence. By leading Gd3+ (1.2 mol%) into Ho3+(0.5 mol%)/Pr3+(0.1 mol%) incorporated Na5Lu9F32 single crystal, the emission intensity at ∼ 2.85 μm was fulfilled significantly about two times enhancement. The destruction of [Ho3+-Ho3+] ion quench clusters and release more luminescent ions are in charge of the enhancement of the emission at 2.85 μm by leading Gd3+ into the fluoride single crystal. The maximum emission cross-section, ∼5.2 × 10−20 cm2, at ∼2.85 μm was estimated on the basis of the emission spectra. Thus, the grown Pr3+/Ho3+/Gd3+ incorporated Na5Lu9F32 fluoride single crystals could be an excellent candidate for source of ∼2.85 μm mid-infrared solid-state laser device.

Original Na5(Lu1–x–yGdxYy)9F32: Pr3+/Ho3+ Hybrid Single Crystals for Efficient ∼2.9 μm Mid-Infrared Emission

A novel Ho3+/Pr3+/Y3+/Gd3+ multiply doped Na5Lu9F32 mixed single crystal was successfully grown via a modified Bridgman technique. The structure of the mixed crystal was characterized by means of X-ray diffraction and Raman spectra. The impacts of Y3+ and Gd3+ ions on the 2.9 μm emission of Na5Lu9F32 single crystals, which incorporated fixed Ho3+/Pr3+, were investigated systematically with the aid of the optical spectra and decay curves of fluorescence. The 2.9 μm emission intensity (Ho3+: 5I6 → 5I7) was further heightened upon gradually introducing both Y3+ and Gd3+ ions into Ho3+/Pr3+-incorporated single crystals pumped at 640 nm. The brokenness of ionic quenching clusters of [Ho3+–Ho3+] and the release of more luminescent ions are in charge of the augment of emission at 2.9 μm by introducing Gd3+ or Y3+ ions into the Ho3+/Pr3+ codoped single crystals. A value of ∼8.2 × 10–21 cm2 was estimated for the maximum emission cross section at 2.9 μm of the mixed crystal. The processing of energy transfer among Ho3+, Pr3+, Y3+, and Gd3+ ions was investigated, and the energy transfer efficiency for Ho3+: 5I7 → Pr3+: 3F2 was approximately 57.32%. The Na5Lu9F32-doped Ho3+/Pr3+/Y3+/Gd3+ mixed crystals may be a new laser gain medium for 2.9 μm generation because of their special spectral and physicochemical properties.

Enhanced red and green up-conversion in Er3+-Yb3+ doped Na5Lu9F32 single crystals through Tb3+ incorporation

Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals were prepared by a Bridgman method. The spectroscopic characteristics of the synthesized single crystals were systematically investigated. Intense green and red emissions originated from transitions for Er3+ and Tb3+ ions were observed. It was found that the introduction of Tb3+ ions to the Er3+/Yb3+ co-doped single crystals can effectively adjust the emission from near-infrared (NIR) to visible region for Er3+ ions. The emissions at 660, 522 and 542 nm from Er3+/Yb3+ co-doped single crystals were enhanced as the Tb3+ concentration increases. The energy transfer mechanisms among Er3+, Yb3+ and Tb3+ ions were also discussed. Analysis on the decay curves suggests that electric dipole-dipole is dominant for the energy transfer from Tb3+ to Er3+ ions. According to the measured lifetimes of Er3+/Yb3+ and Er3+/Yb3+/Tb3+ doped samples, the maximum energy transfer efficiency from Tb3+ to Er3+ approaches up to 11.7%. The intense green and red up-conversion observed in the Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals make them promising candidates for solid-state multicolor displays, temperature sensors, and biomedical imaging applications.

Adjustable multicolor emission from the combination of up-conversion in Tm3+/Tb3+/Yb3+ tri-doped Na5Lu9F32 single crystals

Cubic Na5Lu9F32 fluoride single crystals tri-doped with various Tm3+/Tb3+/Yb3+ concentrations were grown by an improved Bridgman method. The absorption spectra and fluorescence spectra of Tm3+/Tb3+/Yb3+ tri-doped Na5Lu9F32 single crystal were studied systematically. The colors of up-conversion (UC) luminescence could be tuned effectively by adjusting both the doing rare earth ion concentration and the excitation laser power. The chromaticity coordinate and correlated color temperature (CCT) of the emission from the combination of the above up-conversion lights vary from (0.248, 0.261) and 18250 K to (0.325, 0.400) and 5744 K as the Tm3+/Tb3+/Yb3+ doping concentration change from 0.3 mol% Tm3+/0.3 mol% Tb3+/1 mol% Yb3+ to 0.3 mol% Tm3+/0.8 mol% Tb3+/1 mol% Yb3+ excited by a 980 nm radiation. A favorable white light emission with chromaticity coordinates of (0.297, 0.322) could be obtained from Tm3+ (0.3 mol%)/Tb3+ (0.6 mol%)/Yb3+ (1 mol%) tri-doped Na5Lu9F32 single crystal. Two-photon and three-photon absorptions dominated in the conversion processes from the infrared to visual luminescence revealed with the help of the relationship between the up-conversion emission intensity and the excitation pump power. The probable mechanism in charge of the color change of UC in Tm3+/Tb3+/Yb3+ ion doped single crystal was investigated.

Enhanced UC red emission in Ce3+/Yb3+/Ho3+ tri-doped Na5Lu9F32 single crystals

The Na5Lu9F32 single crystals doped with Yb3+/Ho3+ in 1 mol%/6 mol% and various concentrations of Ce3+ (0, 1.0 mol%, 3.0 mol%, 6.0 mol%) for the up-conversion (UC) luminescence were prepared by an improved Bridgman method. Green and red UC emissions at 545 and 658 nm corresponding to the transitions of 5S2/5F4 → 5I8 and 5F5 → 5I8 of Ho3+ ions, respectively, were observed under 980 nm excitation. The emission color and relative intensity can be effectively adjusted from green to red by varying the Ce3+ concentration from 0 to 6 mol%. A nearly pure red UC emission at 658 nm can be obtained when Ce3+ content reaches 6 mol% and Yb3+/Ho3+ are hold at 1 mol%/6 mol%. Pump power dependent measure reveals that both UC emissions at 545 and 658 nm involve a two-photon process. The cross-relaxation processes of 5S2/5F4 (Ho3+) + 2F5/2 (Ce3+) → 5F5 (Ho3+) + 2F7/2 (Ce3+) and 5I6 (Ho3+) + 2F5/2 (Ce3+) → 5I7 (Ho3+) + 2F7/2 (Ce3+) between Ho3+ and Ce3+ ions are responsible for the quenching of green emission and the enhancement of red emission.

Fluorescence Properties of Eu3+ Doped in Na5Lu9F32 Single Crystals

Eu3+ ion doped cubic Na5Lu9F32 single crystals with high quality were synthesized by a modified Bridgman method by using a high 70–90 °C/cm temperature gradient for cross solid-liquid interface. The optical spectroscopic investigations of the obtained single crystal were reported for the absorption, excitation and emission. The experimental results show that a strong red emission at 609 nm attributing to the 5D0→7F2 transition of Eu3+ doped Na5Lu9F32 single crystals can be obtained under the excitation of 394 nm light and reach the maximum when the Eu3+ doping concentration is 4mol% in present research. The local covalent is enhanced and symmetry is reduced with the increase of Eu3+ concentrations inferring from the strength parameters Ω2 and Ω4 calculated by their measured emission spectra. The CIE chromaticity coordinates of the 4mol% Eu3+ doped Na5Lu9F32 single crystals are calculated as (x=0.626, y=0.3736), which are close to the NTSC standard values for red (x=0.67, y=0.33). The experimental results reveal that the single crystal can be used as potential red phosphors under near ultraviolet (NUV) light excitation.

Efficient up-conversion Yb3+, Er3+ co-doped Na5Lu9F32 single crystal for photovoltaic application under solar cell spectrum excitation

Yb3+/Er3+ co-doped Na5Lu9F32 single crystals used as a spectral up-converter to improve the power conversion efficiency of perovskite solar cells are prepared via an improved Bridgman approach. Green and red up-conversion (UC) emissions under the excitation of near-infrared (NIR) bands of 900–1000 nm and 1400–1600 nm can be observed. The effectiveness of the prepared materials as a spectral converter is verified by the enhancement of power conversion efficiency of perovskite solar cells. The sample with a UC layer is 15.5% more efficient in converting sunlight to electricity compared to the UC layer-free sample due to the absorption of sunlight in the NIR range. The results suggest the synthesized Yb3+/Er3+ co-doped Na5Lu9F32 single crystals are suitable for enhancing the performance of perovskite solar cells.

Pr3+掺杂Na5Lu9F32单晶发光性能的优化

Pr³⁺掺杂Na₅Lu₉F₃₂单晶发光性能的优化

Dual-model up/down conversion luminescence of Tm3+/Yb3+/Nd3+ tri-doped Na5Lu9F32 single crystals

Na5Lu9F32 single crystals doped with Tm3+, Yb3+ and Nd3+ ions, have been successfully prepared by an improved Bridgman method. The dual-model up/downconversion luminescence was investigated under near-infrared (NIR) light (800 nm) excitation. The Tm3+, Yb3+, Nd3+ tri-doped Na5Lu9F32 single crystals exhibit intense up-converted blue emission at 488 nm, which correspond to the 1G4→3H6 transitions of Tm3+ ions, the green and yellow emissions at 532 and 589 nm be ascribed to 2G7/2 → 4I9/2 and 2G7/2 → 4I11/2 transitions of Nd3+, respectively. Meanwhile, three emission bands originating from Nd3+ around 860–900, 1060, and 1320 nm in the NIR region can also be observed. The up/down-conversion luminescence intensity was further enhanced by increasing Nd3+ concentration. The lifetime of Yb3+ around 980 nm (307 μs) and Nd3+ at 1060 nm (17.96 μs) were measured. The energy transfer processes in the Yb3+, Tm3+, Nd3+ tri-doped Na5Lu9F32 single crystal have been investigated and discussed.

Optical properties of Cr3+ doped Na5Lu9F32 single crystals grown by the Bridgman method

The growth of Na5Lu9F32 single crystals doped with Cr3+ ions in 0.1 mol%, 0.2 mol% and 0.5 mol% concentrations by Bridgman method was reported. The optical absorption and luminescence spectra decisively demonstrate that the Cr dopant enters Na5Lu9F32 as Cr3+. Fluorescence emission at wavelengths of 418 nm, 444 nm, 653 nm and 678 nm can be observed under the excitation of 372 nm and the fluorescence lifetime at 418 nm was measured to be ∼10.31 μs. The possible crystal sites for Cr3+ ions in Na5Lu9F32 single crystal were discussed, and the lattice parameter Dq, Racach parameters B and C were estimated.

Efficient NIR-NIR upconversion in Na5Lu9F32: Yb3+, Tm3+ single crystals

Na5Lu9F32: Yb3+, Tm3+ single crystals prepared by an improved Bridgman method are expected to be incorporated into solar cells as an upconversion layer to expand the absorption range. Upconversion (UC) with weak emission of 488 nm blue, 704 nm red and strong 805 nm near-infrared fluorescence upon 964 nm excitation as well as its pump power dependence on UC emission were obtained in the single crystals. Furthermore, a high external quantum efficiency (EQE) of 2.65% is obtained for Na5Lu9F32: 8%Yb3+, 1%Tm3+ under 1 W/cm2 980 nm excitation. Meanwhile, the temperature-dependent UC emission spectra is studied as a function of temperature in the range of 250–370 K. The cubic dependence of pump power on UC emission reveals that three-photon UC processes are mainly responsible for the 488 nm, 704 nm emissions and the quadratic dependence indicates two-photon process for the 805 nm emission in Tm3+/Yb3+ co-doped Na5Lu9F32 single crystals, respectively. The energy transfer processes were studied based on energy level diagram, and the results indicated that the cross-relaxation (CR) between Tm3+ and Tm3+ affect the luminous intensity. Moreover, it can infer that the energy transfer from Tm3+ to Yb3+ exists from the decay curves of Tm3+ at 805 nm under excitation by 964 nm.

NIR Downconversion and Energy Transfer Mechanisms in Tb3+/Yb3+ Codoped Na5Lu9F32 Single Crystals.

Tb3+/Yb3+ codoped Na5Lu9F32 single crystals with near-infrared (NIR) emission are achieved by an improved Bridgman approach. Energy transfer from Tb3+ to Yb3+ ions is affirmed by the photoluminescence (PL) emission spectra and decay curves characterization. On the basis of the analysis of energy transfer rate dependence on the Yb3+ concentration, the interaction between Tb3+ and Yb3+ ions in Na5Lu9F32 single crystals is confirmed through the one-to-one energy transfer process. Results demonstrate that the prepared Na5Lu9F32 single crystals might be promising candidates to convert sunlight to improve the performance of the silicon solar cells.

Spectral Characteristics of Mn2+ Doped Na5Lu9F32 Single Crystals

Mn2+ ion doped Na5Lu9F32 single crystals are grown by an improved Bridgman method. The absorption and fluorescence spectrum of single crystals in the range of 300–800 nm are measured to investigate the spectral properties. Fluorescent band centered at 550 nm was observed in the fluorescence spectrum of the crystals corresponding to the 4T1(4G) → 6A1(6S) transition of the Mn2+ ion. An excitation peak of 400 nm is observed in the excitation spectrum due to the charge transfer transition of electrons from the ground state to the conduction band. The calculated values for the crystal field (Dq) and Racah parameters indicate that a stable cubic crystal structure of Mn2+ ion surrounded by eight F− ligands can be formed with the introduction of Mn2+ ion into Na5Lu9F32 single crystals.

Intense 2.0 µm emission from Ho3+/Yb3+ co-doped Na5Lu9F32 single crystal excited by 980 nm

This paper reported on optical spectra of Na5Lu9F32 single crystals co-doped with ~ 0.91 mol% Ho3+ and various Yb3+ concentrations by using an improved Bridgman method. The emission spectra and fluorescence decay curves were measured to investigate the luminescent properties of the Ho3+/Yb3+ co-doped Na5Lu9F32 and the energy transfer process from Yb3+ to Ho3+ ion. Compared with the Ho3+ singly doped Na5Lu9F32 crystal, the Ho3+/Yb3+ co-doped crystal had an obviously enhanced emission at 2.0 µm via the 980 nm laser diode excitation because of the efficient energy transfer from Yb3+ to Ho3+ ion. The maximum emission intensity at 2.0 µm was obtained at about 6.99 mol% Yb3+ concentration when the concentration of Ho3+ ions is fixed at ~ 0.91 mol% in the current research. The maximum emission cross section of the above sample at 2.0 µm was calculated to be 1.23 × 10−20 cm2 according to the measured emission spectrum. The energy transfer efficiency from Yb3+:2F5/2 to Ho3+:5I6 for the crystal was estimated up to 90.8% indicating that Yb3+ ions can efficiently sensitize the Ho3+ ions.

Efficiently Cooperative Energy Transfer Up‐Conversion Luminescence in Tb3+ /Yb3+ Co‐Doped Cubic Na5Lu9F32 Single Crystals by Vertical Bridgman Method

AbstractTb3+/Yb3+ co‐doped Na5Lu9F32 single crystals with ≈1.0 mol% Tb3+ concentrations and various Yb3+ are prepared by Bridgman method. Several visible up‐conversion (UC) luminescence are observed following the excitation of 980 nm laser diode (LD) as well as its pump power dependence on UC emission of the crystals. The quadratic dependence of pump power on UC emission reveals that two‐photon UC processes are mainly responsible for the 486 nm and 543 nm emissions of Tb3+/Yb3+ co‐doped system in Na5Lu9F32 single crystals. It is proposed that cooperative energy transfer (CET) from two excited Yb3+ ions to the ground state of Tb3+ ions is in charge of the ≈486 nm, ≈543 nm and ≈620 nm, which are attributing to 5D4 → 7F6, 5D4 → 7F4 and 5D4 → 7F3, respectively, are obtained in Tb3+/Yb3+ doped Na5Lu9F32 single crystals. Furthermore, a favorable yellowish green light performance can be achieved with certain Yb3+ concentrations and 1.0 mol% Tb3+ co‐doped samples, and its external quantum efficiency approached to 1.25% under 5.5 W cm−2 980 nm excitation which makes further research valuable in developing processable UC materials for electro‐optical devices.

Investigation of the growth and optical properties of a Co2+-doped Na5Lu9F32 single crystal

Investigation of the growth and optical properties of a Co2+-doped Na5Lu9F32 single crystal

Highly efficient up-conversion luminescence in Er3+/Yb3+ co-doped Na5Lu9F32 single crystals by vertical Bridgman method

Er3+/Yb3+ co-doped Na5Lu9F32 single crystals with different concentrations of Yb3+ ions were prepared to investigate their phase structure, up-conversion (UC) properties and mechanism of UC luminescence by Bridgman method. Under 980 nm near-infrared (NIR) excitation, three sharp UC emission bands topping at green ~525 nm, ~548 nm and red ~669 nm were obtained in Er3+/Yb3+ doped Na5Lu9F32 single crystals which are attributing to the transitions of 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2, respectively. The quadratic dependence of pump power on UC emission indicated that two-photon process is in charge of the transition from excited state of Yb3+ ions to lower state of Er3+ ion in Na5Lu9F32 single crystals. The long-accepted mechanism for the production of red and green emissions through up-conversion (UC) under 980 nm excitation in Er3+/Yb3+ co-doped materials apply in the Na5Lu9F32 host was displayed. The enhancement of the red emission was observed due to a cross-relaxation (CR) process of the form: 4F7/2 + 4I11/2 → 4F9/2 + 4F9/2. Furthermore, an ideal yellowish green light performance could be achieved with 1.0 mol% Er3+ doped certain Yb3+ concentrations samples, and its external quantum efficiency approached to 6.80% under 5.5 Wcm−2 980 nm excitation which can be applied in developing UC displays for electro-optical devices.