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LiBaPO 4 : Tb3+, Dy3+ phosphors were prepared via sol-gel method by using the stoichiometric amounts of lithium nitrate LiNO 3, barium nitrate Ba(NO 3) 2 and ammonium dihydrogen phosphate NH 4 H 2 PO 4 as base materials. Morphology by scanning electron microscopy (SEM), structure by X-ray diffraction (XRD), thermal properties by Differential thermal analysis (DTA)/Thermogravimetric Analysis (TGA) and structural characteristics by Fourier transform infrared spectroscopy (FT-IR) were investigated. This paper presents luminescence properties using spectra from radioluminescence (RL), photoluminescence (PL), cathodoluminescence (CL) and, thermoluminescence (TL) and the influence of RE dopants (Tb3+, Dy3+) on the luminescent behavior of LiBaPO 4. Computerized Glow Curve Deconvolution (CGCD) and Peak Shape Method were used to determine the kinetic parameters and the obtained results were evaluated. The RL results of un-doped LiBaPO 4 showed the presence of a well-defined peak at 417 nm and a weaker band around 685 nm. Strong emissions were detected in the sample doped with Dy3+ correspond to 4F 9/2 →6H j transitions. Blue, yellow and red emissions were observed with transitions of 4F 9/2 → 6H 15/2 , 4F 9/2 → 6H 13/2 and 4F 9/2 → 6H 11/2 , respectively. As for LiBaPO 4 : Tb3+, green emissions originated from the characteristic transitions (5D 3 → 7F J (j = 6–3) and 5D 4 → 7F J (j = 6–1)) of Tb+3 ion was seen. The RL, PL and CL spectra were identical, suggesting these green emissions. Dy3+ doped sample has three glow curves located at 72 °C, 145 °C and 204 °C, while the main temperature peak is measured at 240 °C for Tb3+ doped sample. Chromotographic studies of LiBa 0·98 PO 4 : Dy3+ 0.02 reveals that calculated x and y color coordinates (0.3122, 0.3233) are very close to the white light. • Dy3+ and Tb3+ doped LiBaPO 4 phosphors were successfully synthesized by sol-gel process. • XRD results of Tb3+ doped LiBaPO 4 ceramics showed that the single-phase is preserved. • Thermoluminescence, radioluminescence and SEM-CL analysis of LiBaPO 4 : Tb3+, Dy3+ phosphors were studied. • The Peak Shape (PS) method and the Computerized Glow Curve Deconvolution (CGCD) were used to estimate the kinetic parameters. [ABSTRACT FROM AUTHOR]

A novel phosphor LiBaPO4 doped with rare earths Eu and Dy prepared by high temperature solid-state reaction method is reported. The phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The emission and excitation spectra of these materials were measured at room temperature with a spectrofluorophotometer. The excitation spectra of LiBaPO4:Eu3+ phosphor can be efficiently excited by 394 nm, which is matched well with the emission wavelength of near-UV light-emitting diode (LED) chip. PL properties of Eu3+-doped LiBaPO4 exhibited the characteristic red emission coming from 5D0 → 7 F1 (593 nm) and 5D0 → 7 F2 (617 nm) electronic transitions with color co-ordinations of (0.680, 0.315). The results demonstrated that LiBaPO4:Eu3+ is a potential red-emitting phosphor for near-UV LEDs. Emission spectra of LiBaPO4:Dy3+ phosphors showed efficient blue (481 nm) and yellow (574 nm) bands, which originated from 4 F9/2 → 6H15/2 and 4 F9/2 → 6H13/2 transitions of the Dy3+ ion, respectively. The 574 nm line is more intense than the 481 nm lines, which indicates that the site Dy3+ is located with low symmetry. This article summarizes fundamentals and possible applications of optically useful inorganic phosphates with visible photoluminescence of Eu3+ and Dy3+ ions. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: The lithium barium orthophosphate LiBaPO4 compound has been synthesized by the classic ceramic method and characterized by X-ray diffraction (XRD) technique. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 681–872K and 200Hz–1MHz respectively by means of impedance spectroscopy. The activation energy value of LiBaPO4 sample is bigger than of the LiMPO4 (M=Mn, Co, Ni, Fe) compounds. The frequency dependent conductivity of the present system shows the power law feature. Dielectric data were analyzed using complex electrical modulus M* at various temperatures. The peak positions ω m of the above spectra shift towards higher frequencies with increase in temperature. The above spectra have been characterized in terms of Kohlrausch–Williams–Watts (KWW) relaxation function to understand relaxation behavior. The activation energy responsible for relaxation calculated from the modulus spectra is found to be almost the same as the value obtained from temperature variation of dc conductivity. The electrical modulus and its scaling behavior are also investigated and the relationship between power-law exponent n and stretched exponential exponent β is found. [Copyright &y& Elsevier]

Near-ultraviolet (near-UV) pumped white light-emitting diodes (w-LEDs) based on tri-color (blue/green/red) phosphors have been regarded as an important approach to realize high-quality solid-state lighting, but the cyan gap between the blue and green phosphors imposes a limitation on the color rendering index. To solve this problem, efficient cyan phosphors with emission peaking around 490 nm and broad absorption band in the near-ultraviolet range are urgently needed. Herein, we demonstrate an efficient near-UV-excitable cyan-emitting LiBaPO 4 :Eu2+ orthophosphate phosphor for high-color-rendering w-LEDs. The prepared LiBaPO 4 :Eu2+ phosphors show a broad excitation band in the wavelength range of 250–450 nm peaking at 353 nm. Under 353 nm excitation, LiBaPO 4 :Eu2+ phosphors produce a wide cyan emission band in the wavelength range of 400–700 nm with a peak about 485 nm and bandwidth of 99 nm. More importantly, LiBaPO 4 :Eu2+ phosphors exhibit a high internal quantum efficiency of 88.3%. A w-LED device is fabricated with a 365 nm near-UV LED chip with LiBaPO 4 :Eu2+ cyan phosphors and commercial CaAlSiN 3 :Eu2+ red phosphors, which demonstrates bright white emission with a color rendering index of 84.2 and correlated color temperature of 5243 K. Efficient Eu2+-doped LiBaPO 4 cyan phosphors are developed for near-UV-pumped white LEDs with high color rendering index. [Display omitted] • An efficient near-UV-excitable cyan-emitting LiBaPO 4 :Eu2+ phosphor is reported. • The excitation band is located in the 250–450 nm range peaking at 353 nm. • Broadband cyan emission with peak at 485 nm and bandwidth of 99 nm is observed. • Internal quantum efficiency is measured to be 88.3%. • A white LED device with color rendering index of 84.2 is fabricated. [ABSTRACT FROM AUTHOR]

We investigated the emission properties of Eu ion-doped A BaPO 4 (A BaPO 4 :Eu, A = Li, Na, and K) in which the valence state of the Eu ions was controlled by annealing in various ambients, gamma-ray (γ-ray) irradiation, and hydrogen ion (H+) implantation. We synthesized the A BaPO 4 :Eu samples by solid-state reaction in air. The as-synthesized samples showed sharp red emission near 600 nm, which originated from Eu3+ ions. Interestingly, annealing under H 2 ambient changed the valence state of the Eu ions from 3+ to 2+, which was indicated by the disappearance of the red emission and concurrent emergence of strong blue emission. After subsequent annealing in O 2 atmosphere, the red emission of Eu3+ was recovered. The reversible switching between the 2+ and 3+ states was found to be repeatable by alternating H 2 and O 2 annealing. The valence state was also changed from 3+ to 2+ by H+ implantation and γ-ray irradiation of the as-synthesized samples, possibly owing to the formation of oxygen vacancies. Our results suggest that the luminescence color of the A BaPO 4 :Eu phosphors can be controlled within a range from red to blue by simple annealing in various ambients. • Both Eu2+ and Eu3+ luminescences were investigated in ABaPO 4 (A = Li, Na, and K). • The valence states of Eu ions changed reversibly through the H 2 - and O 2 -ambient post-annealing. • The valence states of Eu ions could be changed by gamma-ray irradiation and H+-implantation. • The color of Eu ion doped ABaPO 4 phosphors can be tuned easily in a range from red to blue by post-treatments. [ABSTRACT FROM AUTHOR]

A novel phosphor LiBaPO4 doped with rare earths Eu and Dy prepared by high temperature solid-state reaction method is reported. The phosphors were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL). The emission and excitation spectra of these materials were measured at room temperature with a spectrofluorophotometer. The excitation spectra of LiBaPO4:Eu(3+) phosphor can be efficiently excited by 394 nm, which is matched well with the emission wavelength of near-UV light-emitting diode (LED) chip. PL properties of Eu(3+)-doped LiBaPO4 exhibited the characteristic red emission coming from (5) D0 → (7) F1 (593 nm) and (5) D0 → (7) F2 (617 nm) electronic transitions with color coordinations of (0.680, 0.315). The results demonstrated that LiBaPO4:Eu(3+) is a potential red-emitting phosphor for near-UV LEDs. Emission spectra of LiBaPO4:Dy(3+) phosphors showed efficient blue (481 nm) and yellow (574 nm) bands, which originated from (4) F9/2 → 6) H15/2 and (4) F9/2 → (6) H13/2 transitions of the Dy(3+) ion, respectively. The 574 nm line is more intense than the 481 nm lines, which indicates that the site Dy(3+) is located with low symmetry. This article summarizes fundamentals and possible applications of optically useful inorganic phosphates with visible photoluminescence of Eu(3+) and Dy(3+) ions., (Copyright © 2015 John Wiley & Sons, Ltd.)