Tetragonal YPO4 Research Articles

DUV electroluminescence from Bi3+-doped bi-phase yttrium phosphate

Trivalent-doped tetragonal xenotime yttrium orthophosphate phosphors have attracted significant attention as promising materials for deep ultraviolet (DUV) luminescence. In this study, we achieved DUV electroluminescence (EL) using Bi3+-doped bi-phase yttrium phosphate (YPB) phosphor under an AC-driven sinusoidal waveform. Phosphor powder was synthesized via a solid-state reaction with an optimal Bi3+ concentration. The phosphor exhibited a mixed phase of xenotime tetragonal YPO4 and monoclinic Y(PO3). We suggest that the mixed phase within the phosphor particles plays a crucial role in enhancing light generation via a bipolar field emission mechanism in the developed powder-based EL device. It emitted a narrow-band DUV emission spectrum peaking at 243 nm, which was attributed to the 3P1 → 1S0 transition of the Bi3+ ions within the mixed host lattices. Moreover, it has a lower voltage application than the excimer lamp DUV sources. The application of the YPB phosphor in EL devices presents an appealing outlook for future advancements in the development of DUV sources.

Synthesis, structure, and photoluminescence analysis of thermally stable Sm3+ doped YPO4 phosphor

In this manuscript, we used the coprecipitation method to manufacture Sm3+ doped YPO4. To verify the phase and structural properties of the synthesized material, we performed XRD. The diffraction patterns of the synthesized sample match the tetragonal YPO4 with no indication of an impurity peak, demonstrating the creation of a pure phase. The photoluminescence excitation and emission profiles of the synthesized material were recorded. Characteristic excitation and emission peaks of Sm3+ were observed. The distinctive orange-reddish emission of Sm3+ is found at the highest intense excitation peak (404 nm). The CIE spectral coordinates of the phosphor are (0.6080,0.3912). The emission spectra are recorded under various excitation levels. The temperature-dependent emission under 404 nm excitation is also observed to confirm the thermal stability of the synthesized material. The emission intensity drops just 13% up to 150 °C, indicating the material’s remarkable thermal stability. These findings indicate that the synthesized material is suitable for application in display devices.

Roles of (NH4)2HPO4 and NH4H2PO4 in the phase transition and luminescence enhancement of YPO4:Eu

Investigating crystal phase transition helps in understanding new crystal structures and obtaining novel performance. The conventional approaches to realizing phase transition usually require extreme conditions such as high temperature, high pressure, or heavy ion doping. In this work, we achieve phase transition from hexagonal to tetragonal YPO4:Eu crystals just by increasing the concentration ratio of (NH4)2HPO4 to NH4H2PO4 in the precursor. When increasing the ratio, the underlying transition mechanism modifies the free energy of the crystalline system and in turn selects the tetragonal phase with higher formation energy. The difference in preferred growth direction endows tetragonal and hexagonal microcrystals with sphere- and prism-like morphology, respectively. The luminescence intensity is stronger in the tetragonal than the hexagonal phase, due to stronger non-radiative energy transfer induced by high-frequency vibrations in the hexagonal lattice. The efficient method provided here allows convenient production of tetragonal samples with high luminescence intensity on a large scale, and could be well applied to other phosphate systems for phase selection.

New physical insight into crystal structure, luminescence and optical properties of YPO4:Dy3+∖Eu3+∖Tb3+ single-phase white-light-emitting phosphors

A novel single-phase white-light-emitting YPO4 phosphor, single and co-doped with Dy3+/Eu3+, aiming at UV-pumping in white-light-emitting diodes (WLEDs) which exhibits an outstanding optical performance, was successfully produced. The crystal structure, the morphology, the electronic band structure, the electronic configuration, and the bond length of the prepared phosphors were thoroughly investigated, both experimentally and by computational methodology. The results showed that the host lattice provides various surrounding environments to the Eu3+ activators is a results of Eu3+ single and Dy3+/Eu3+ co – doped YPO4 phosphors. Under ultra-violet (UV) excitation (353 nm), the prepared tetragonal phase YPO4:Dy3+ phosphors emitted a bluish-white-light because it has peaks of similar intensity in the blue and the yellow spectral region. The emission spectrum can be tuned from bluish white to green/yellow/red and warm white by adjusting the concentration of Tb3+/Eu3+ dopants. A high photoluminescence quantum yield (PLQYs) 68.55% was achieved. It was observed that the tetragonal YPO4:Tb3+/Dy3+/Eu3+ phosphors emit-white-light which covers the whole visible region, and have good thermal stability from 20 to 200 °C. Finally, a WLED was fabricated by using a UV LED (365 nm) chip coated with the optimized YPO4:Tb3+/Dy3+/Eu3+ single-phase phosphor, demonstrating an excellent white-light emission with a high CRI value (Ra = 92) and a low CCT value (Tc = 2497 K). Hence, the produced material is a promising candidate for UV-pumped single-phase phosphor-converted WLEDs.

Synthesis and photoluminescent properties of Y1 − x La x PO4:Eu3+ nanophosphor

In this paper, Y1 − x La x PO4:Eu3+ (x = 0.5, 0.7, and 0.3) nanophosphors were synthesized by a rather simple method. The products present different morphologies. For Y1 − x La x PO4:Eu3+, they have similar phase composition of a mixture of monoclinic LaPO4 and tetragonal YPO4. Furthermore, the luminescence behavior of Eu3+ has been investigated in this type of matrices. In Y1 − x La x PO4:Eu3+, the 5D0-7F1 magnetic dipole transition is dominant, indicating that the Eu3+ site is inversion symmetry. The difference in the Eu-O charge transfer (CT) band with La3+ ion concentration suggests the difference in the ionicity of the Eu-O bond. Among those products, the red to orange intensity ratio (R/O) of 5D0-7F2 to 5D0-7F1 value of Eu3+ is different, furthermore, for La3+ x = 0.3, the R/O value of Eu3+ is the biggest on the contrary, indicating that the inversion symmetry Eu3+ is lowest.

Effects of Bi3+ co-doping on luminescence of YPO4:Dy3+ powders

YPO4:Dy3+ powders co-doped with Bi3+ ions were synthesized successfully by solid state reaction. XRD and IR results show that all samples are well crystallized to a pure tetragonal YPO4. The EDX spectra suggest that Dy3+ and Bi3+ ions co-doped in the YPO4 host materials successfully. The emission spectra of synthesized samples show two emission bands originated from the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ ions. The co-doped Bi3+ ions can improve the luminescence intensities of YPO4:Dy3+ phosphors effectively. The highest emission intensity is obtained when the co-doped concentration of Bi3+ ions reaches a value of 3mol%.

CTAB assisted hydrothermal preparation of YPO4:Tb3+ with controlled morphology, structure and enhanced photoluminescence

In this paper, we report a simple and convenient method toward fabrication of YPO4:Tb3+ with controlled structures, morphologies and enhanced luminescent properties. By simply controlling the amount of the cetyltrimethyl ammonium bromide (CTAB) during the hydrothermal process, tetragonal YPO4:Tb3+ and hexagonal YPO4·0.8H2O:Tb3+ with nanoparticle and olive-like nanoparticle can be obtained, respectively. Meanwhile, we find that the structures and morphologies can affect their luminescent properties obviously and the intensity of the samples with hexagonal phase is evidently higher than that with tetragonal phase. The variation of crystal structures, morphologies of the samples are ascribed to the crucial role of CTAB during the fabrication process that acts as complexing reagent and inducing agent and the mechanism was also discussed. We believe the method reported here will open a novel approach to rare earth phosphates with multiple structures.

Nucleation sequence on the cation exchange process between Y0.95Eu0.05PO4 and CePO4 nanorods

Nanorods of Y0.95Eu0.05PO4@CePO4 (Y0.95Eu0.05PO4 phase was nucleated first and then a CePO4 phase was nucleated) and CePO4@Y0.95Eu0.05PO4 (CePO4 phase was nucleated first and then Y0.95Eu0.05PO4 phase was nucleated) were prepared at a relatively low temperature of 140 °C in ethylene glycol medium. Based on XRD, TEM and Raman studies it has been inferred that Y0.95Eu0.05PO4@CePO4 sample consists of a mixture of bigger (length around 800-1000 nm and width around of 80-100 nm) and smaller (length around 70-100 nm and width around 10-20 nm) nanorods, having monoclinic CePO4 and tetragonal YPO4 structure, whereas CePO4@Y0.95Eu0.05PO4 sample consists of mainly small nanorods having a single phase CePO4 structure. From the detailed luminescence studies it has been established that there exists significant incorporation of Y3+/Eu3+ ions in the CePO4 phase in CePO4@Y0.95Eu0.5PO4 sample. This has been attributed to the cation exchange taking place between Ce3+ ions in CePO4 host and Eu3+ and Y3+ ions in solution during the synthesis stage. Unlike this, such an exchange is not possible for Y0.95Eu0.05PO4@CePO4 sample synthesized under identical conditions due to the higher solubility product (Ksp) value of YPO4 compared to CePO4. Incorporation of Eu3+ in the CePO4 lattice of CePO4@Y0.95Eu0.5PO4 sample is confirmed by the significant reduction in the lifetime of 5D0 level of Eu3+ and the luminescence intensity from Eu3+, arising due to the electron transfer between the Ce3+/Ce4+ and Eu3+/Eu2+ species. These results are further supported by the non-radiative decay rates and quantum yields calculated from the emission spectrum.

Deformation Mechanisms in Refractory Rare-Earth Phosphates

AbstractA method for prediction of deformation twin modes from analysis of the necessary atomic shuffles was developed for monazite (monoclinic LaPO4). This method is applied to scheelite (tetragonal CaWO4), xenotime (tetragonal YPO4), and zircon (tetragonal ZrSiO4). The predictions are compared to observations in these materials. Merit of the predictive method is discussed.