Synthesis and Luminescence Properties of a CsBaGd(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript>:Er<Superscript>3+</Superscript> Phosphor with a Scheelite-Like Structure

A CsBaGd(MoO₄)₃:Er³⁺ phosphor with a scheelite-like structure (sp. gr. P2₁/n) has been synthesized and its luminescence properties have been studied. The synthesized material has been characterized by X-ray diffraction, differential thermal analysis, Raman spectroscopy, and IR spectroscopy.     

Synthesis and luminescence properties of Tb<Superscript>3+</Superscript>-doped LiMgPO<Subscript>4</Subscript> phosphor

Polycrystalline sample LiMg_(1?x)PO₄:xTb³⁺ (x = 0.001, 0.002, 0.005, 0.01, 0.02) phosphor was synthesized via modified solid state method (MSSM). The prepared sample was characterized through XRD pattern (X-ray diffraction) and SEM (scanning electron microscope). Additionally, photoluminescence (PL), optically stimulated luminescence (OSL), thermoluminescence (TL) and other dosimetric properties including dose linearity, reusability and fading were studied. In OSL mode, sensitivity of prepared phosphor was found to be 2.7 times that of LiMgPO₄:Tb³⁺, B (BARC) phosphor and 4.3 times that of α-Al₂O₃:C (BARC) phosphor. The TL glow consists of overlapping peaks in temperature range of 50–400^°C and first peak (P₁) was observed at 150^°C, second peak (P₂) at 238^°C, third peak (P₃) at 291^°C and fourth peak (P₄) at 356^°C. The TL sensitivity of second peak (P₂) of LiMgPO₄:Tb³⁺ phosphor was compared with α-Al₂O₃:C (BARC) phosphor and found to be 100 times that of the α-Al₂O₃:C (BARC) phosphor. The minimum detectable dose (MDD) was found to be 5.6 μGy. Moreover, photoionization cross-sections, linearity, reusability, fading and kinetic parameters were calculated. Also, photoluminescence spectra of LiMgPO₄: Tb³⁺ shows characteristic green–yellow emission exciting at 224 nm UV source.     

Color-tunable luminescence properties of Sm<Superscript>3+</Superscript>/Dy<Superscript>3+</Superscript> co-doped NaLa(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> phosphors and their energy transfer mechanism

The Sm³⁺, Dy³⁺ doped and Sm³⁺/Dy³⁺ co-doped NaLa(MoO₄)₂ spherical phosphors were hydrothermally synthesized by the EDTA-2Na mediated method. Under the excitation of 297 nm, the quenching concentration of Sm³⁺ in NaLa(MoO₄)₂ host was determined to be 13%, and the concentration quenching mechanism was discussed to be the electric quadrupole–quadrupole interaction. After Sm³⁺ and Dy³⁺ ions were co-doped into the NaLa(MoO₄)₂ host, the energy transfer behaviors resulted from Dy³⁺ to Sm³⁺ ions were investigated by the help of the luminescent spectra of the obtained phosphors. By varying co-doping concentrations of Sm³⁺/Dy³⁺ ions, the emission color of NaLa(MoO₄)₂:Sm³⁺/Dy³⁺ can be tuned from reddish-orange, pink and white to bluish-green. The CIE chromaticity coordinate, the correlated color temperature and the quantum efficiency of NaLa_0.87(MoO₄)₂:1%Sm³⁺, 12%Dy³⁺ were calculated to be (0.356, 0.320), 4353 K and 20%, respectively. Furthermore, in the temperature-dependent analysis, it presented good thermal stability, which can become a promising single-phased white-emitting phosphor for white LEDs devices. Based on these results, the possible energy transfer mechanism between Dy³⁺ and Sm³⁺ in NaLa(MoO₄)₂:Sm³⁺/Dy³⁺ was also proposed.     

Spectral parameters of Er<Superscript>3+</Superscript> ion in Yb<Superscript>3+</Superscript>/Er<Superscript>3+</Superscript>:KY(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

The spectral parameters of Er³⁺ in Yb³⁺/Er³⁺:KY(WO₄)₂ crystal with space group C2/c have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the intensity parameters are: ₂ = 6.33 × 10^–20 cm², ₄ = 1.35 × 10^–20 cm², ₆ = 1.90 × 10^–20 cm². The radiative lifetime and the fluorescence branch ratios were calculated. The emission cross section _e (at 1536 nm) is 2.0 × 10^–21 cm².     

Synthesis and photoluminescence study of narrow-band UVB-emitting LiSr<Subscript>4</Subscript>(BO<Subscript>3</Subscript>)<Subscript>3</Subscript>:Gd<Superscript>3+</Superscript>, Pr<Superscript>3+</Superscript> phosphor

A series of Pr³⁺, Gd³⁺ and Pr³⁺–Gd³⁺-doped inorganic borate phosphors LiSr₄(BO₃)₃ were successfully synthesized by a modified solid-state diffusion method. The crystal structures and the phase purities of samples were characterized by powder X-ray diffraction. Surface morphology of the sample was studied by scanning electronic microscopy (SEM). The optimal concentrations of dopant Gd³⁺ ions in compound LiSr₄(BO₃)₃ were determined through the measurements of photoluminescence (PL) spectra of phosphors. Gd³⁺-doped phosphors LiSr₄(BO₃)₃ show strong band absorption in UV spectral region and narrow-band UVB emission under the excitation of 276 nm was only due to ⁶P _J → ⁸S_7/2 transition of Gd³⁺ ions. The effect of Pr³⁺ ion on excitation of LiSr₄(BO₃)₃:Gd³⁺ was also studied. The excitation of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ gives a broad-band spectra, which show very good overlap with the Hg 253.7 nm line. The photoluminescence spectra of LiSr₄(BO₃)₃ with different doping concentrations Pr³⁺ and keeping the concentration of Gd³⁺ constant at 0.03 mol have also been studied. The emission intensity of LiSr₄(BO₃)₃:Pr³⁺–Gd³⁺ phosphors increases with increasing Pr³⁺ doping concentration and reaches a maximum at 0.01 mol. From the photoluminescence study of LiSr₄(BO₃)₃:Gd³⁺, Pr³⁺ we conclude that there was efficient energy transfer from Pr³⁺→ Gd³⁺ ions in LiSr_4?x?y Pr _x Gd _y (BO₃)₃ phosphors.     

Elastic properties of Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> single crystals

The complete elastic modulus matrix of Li₂Zn₂(MoO₄)₃ single crystals has been measured for the first time. The sound velocity has been measured in different directions of the crystals by a pulse-phase method. The measurement results have been used to calculate elastic moduli. The sound velocity has been calculated in the three main crystallographic planes of the crystals.     

X-ray diffraction,optical absorption and emission studies on Er<Superscript>3+</Superscript>- and Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript>-doped Li<Subscript>3</Subscript>NbO<Subscript>4</Subscript> powder

Er³⁺(/Yb³⁺)-doped Li₃NbO₄ powder were prepared by thermally sintering mixtures of Er₂O₃ (0.5, 1.0 mol%), Yb₂O₃ (0, 0.5, 1.0 mol%), Li₂CO₃ (48–49 mol%) and Nb₂O₅ (50 mol%) at 1125, 1150 and 1450 °C over the durations of 8–22 h. The crystalline phases contained in these samples were determined by using X-ray diffraction and discussed in comparison with a vapor-transport-equilibration-treated (VTE-treated) Er(2.0 mol%):LiNbO₃ single crystal and ErNbO₄ powder previously reported. The results show that the X-ray patterns of the rare-earth-doped samples reveal little difference each other, but large differences with those of the VTE crystal and ErNbO₄ powder. The doped rare-earth ions Er³⁺ (and Yb³⁺) present in the powder as the ErNbO₄ (and YbNbO₄) phase(s). The possibility that the highly Er-doped LiNbO₃ crystal contains Li₃NbO₄ precipitates is small. Optical absorption and emission studies show that the only Er-doped Li₃NbO₄ powder shows similar absorption and emission characteristics with the pure ErNbO₄. The codopant Yb³⁺ ion enhances the 980-nm-upconversion emissions of Er³⁺ ions, results in remarkable spectral alterations at 0.98 μm region, and causes the alterations of relative absorbance and relative emission intensity of individual peaks or bands at 1.5 μm region. On the other hand, the Yb-codoping hardly affects the Er³⁺ energy structure and the lifetime of Er³⁺ ion at 1.5 μm. The measured lifetimes at 1.5 μm of Er³⁺ ions in the singly Er³⁺- and doubly Er³⁺/Yb³⁺-doped mixtures have a nearly same value of ∼ 1.5 ms. For the pure ErNbO₄ powder, the lifetime is prolonged to ∼2 ms perhaps due to radiation trapping effect.     

Sr<Subscript>3</Subscript>GdLi(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F: Sm<Superscript>3+</Superscript> phosphor: preparation and luminescence properties evaluation

A series of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ (x?=?0.02, 0.04, 0.06, 0.08) phosphors were synthesized by a high-temperature solid state method. The Sm³⁺ activated Sr₃GdLi(PO₄)₃F phosphors can be efficiently excited by the wavelengths in the range from 350 to 450 nm, which matches perfectly with that of the commercial near-UV LED chips. The optimal doping concentration of Sr₃Gd_1?xLi(PO₄)₃F: xSm³⁺ phosphors was determined to be x?=?0.04, corresponding to the quantum efficiency of 2.23%, and the CIE chromaticity coordinates (x?=?0.5172, y?=?0.4641). The concentration quenching mechanism of Sm³⁺ in Sr₃GdLi(PO₄)₃F host is mainly attributed to the dipole–dipole interaction, which was confirmed by the fluorescent lifetimes. The effect of temperature on the photoluminescence property of Sr₃GdLi(PO₄)₃F: Sm³⁺ was investigated. 90% of the intensity is preserved at 150 °C. In addition, a white light emitting diode (WLED) lamp was fabricated by a 405 nm n-UV LED chip coated with Sr₃Gd_0.96Li(PO₄)₃F:0.04Sm³⁺ phosphor and commercial yellow phosphor (YAG: Ce³⁺) of a certain mass ratio. The present work indicates that the Sr₃GdLi(PO₄)₃F: Sm³⁺ orange–red-emitting phosphors tend to be potential application in n-UV WLED.     

Synthesis and properties of AgTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-based NASICON-type phosphates doped with Nb<Superscript>5+</Superscript>, Zr<Superscript>4+</Superscript>, and Ga<Superscript>3+</Superscript>

We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent cations for titanium: Ag_1±x Ti_2−x M _x (PO₄)₃ (M = Nb⁵⁺, Ga³⁺) and AgTi_2−x Zr _x (PO₄)₃. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult to replace with protons.     

Synthesis and luminescence properties of LiBaPO<Subscript>4</Subscript>:Bi<Superscript>3+</Superscript> yellow-emitting phosphor for solid-state lighting

Novel LiBaPO₄:Bi³⁺ yellow-emitting phosphor is synthesized by high temperature solid-state reaction method in air. With excitation 260 nm, LiBaPO₄:Bi³⁺ phosphor emits yellow light with the chromaticity coordinate (0.4272, 0.4657) and color rendering index 77.7. Emission band peaking at ~?588 nm of LiBaPO₄:Bi³⁺ phosphor in the range of 400–790 nm is attributed to the ³P₁ → ¹S₀ electron transition of Bi³⁺ ion. Excitation band monitored at 588 nm in the range of 220–300 nm is assigned to the ¹S₀ → ³P₁ electron transition of Bi³⁺ ion. The optimal Bi³⁺ ion concentration in LiBaPO₄:Bi³⁺ phosphor is ~?1.0 mol%. Time resolved spectra and fluorescence lifetime data confirm that there is only Bi³⁺ ion luminous center in LiBaPO₄:Bi³⁺ phosphor. The luminous mechanism is analyzed by configurational coordinate diagram of Bi³⁺ ion. The experiment results are helpful to develop other new Bi³⁺-doped optical materials for solid-state lighting.     

Synthesis and luminescence properties of Eu<Superscript>2+</Superscript>-doped Li<Subscript>2</Subscript>SrSiO<Subscript>4</Subscript>

We have studied the luminescence spectra of Li₂Sr_{1 − x} Eu _x SiO₄ (x = 0.0001–0.01) solid solutions prepared by solid-state reactions and a sol-gel process in a reducing atmosphere. The spectra show a broad band in the range 500–700 nm, centered at 578 nm, which is due to the 4f ⁶5d → 4f ⁷ transition. The luminescence excitation spectrum shows, in addition to bands due to Eu²⁺ 4f ⁷ → 4f ⁶5d transitions, a strong band centered at 174 nm, attributable to absorption in the SiO₄⁴⁻ group.     

Low temperature synthesis and photoluminescence of Ca<Subscript>3</Subscript>(VO<Subscript>4</Subscript>)<Subscript>2</Subscript>:Eu<Superscript>3+</Superscript> nanocrystals with Li<Superscript>+</Superscript> addition

Different crystalline Ca₃(VO₄)₂ nanocrystals have been synthesized successfully via a facile low temperature method with lithium addition. After different ration of Li⁺ doping into the Ca₃(VO₄)₂: Eu³⁺ host, the crystallinity of the sample becomes different, resulting in different of luminescence intensity of the characteristic emission of Eu³⁺ ions. This approach provides economically viable route for large-scale synthesis of this kind of nanomaterials.     

Synthesis and luminescence properties of a novel UV-emitting phosphor Sr<Subscript>3</Subscript>P<Subscript>4</Subscript>O<Subscript>13</Subscript>:Ce<Superscript>3+</Superscript>

The ultraviolet (UV)-emitting Sr₃P₄O₁₃:Ce³⁺ phosphors were synthesized via the solid-state reaction method, and their structural, morphological and luminescence properties were characterized by X-ray diffraction analysis, scanning electron microscopy, photoluminescence spectroscopy. The obtained results indicate that these phosphors can be effectively excited by short-wavelength ultraviolet (<300 nm), and exhibit long-wavelength ultraviolet (300–380 nm) emission with nanosecond-level fluorescence lifetime corresponding to the parity-allowed 5d–4f transitions of Ce³⁺. The concentration-quenching phenomenon of Ce³⁺ in Sr₃P₄O₁₃ host was also studied, in which the critical energy transfer distance between Ce³⁺ ions and concentration quenching mechanism were determined.     

Synthesis of Er<Superscript>3+</Superscript> and Er<Superscript>3+</Superscript> : Yb<Subscript>3+</Subscript> doped sol-gel derived silica glass and studies on their optical properties

Er₃₊ and Er₃₊ : Yb₃₊ doped optical quality, crack and bubble free glasses for possible use in making laser material have been prepared successfully through sol-gel route. The thermal and optical, including UV-visible absorption, FTIR etc characterizations were undertaken on the samples. The absorption characteristics of Er₃₊ doped samples clearly revealed the absorption due to Er₃₊ ions. On the other hand Yb₃₊ : Er₃₊ doped samples showed enhanced absorption due to² F _7/2 →² F _5/2 transition. The absorption and emission cross-section for² F _7/2 ↔² F _5/2 of Yb³⁺ were estimated. FTIR absorption spectra have clearly shown the reduction of the absorption peak intensity with heat treatment in the range 3700–2900 cm⁻¹. The 960 cm^-1 band also showed progressive decrease in the absorption band peak intensity with heat treatment. The result of the investigations with essential discussions and conclusions have been reported in this paper.     

Crystal structure and luminescence property of a single-phase white light emission phosphor Sr<Subscript>3</Subscript>YNa(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>F:Dy<Superscript>3+</Superscript>

A series of single-phase Sr₃YNa(PO₄)₃F:Dy³⁺ phosphors were successfully synthesized via a conventional solid state reaction process. The powder X-ray diffraction patterns were utilized to confirm the phase composite and crystal structure. The phosphor could be excited by the ultraviolet visible light in the region from 300 to 420 nm, and it shown two dominant emission bands peaking at 484 nm (blue light) and 580 nm (yellow light) which originated from the transitions of ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 of Dy³⁺, respectively. The optimum dopant concentration of Dy³⁺ ions was confirmed to be 7 mol% in Sr₃YNa(PO₄)₃F:Dy³⁺ system and the concentration quenching mechanism is dipole–dipole interaction. The lifetime values of Dy³⁺ ions at different concentrations (x?=?0.03, 0.05, 0.07, 0.09 and 0.11) were determined to be about 0.855, 0.759, 0.686, 0.606 and 0.546 ms, respectively. The thermal stability of luminescence of Sr₃YNa(PO₄)₃F:0.07Dy³⁺ phosphor was also investigated and the activated energy was deduced to be 0.228 eV, which shows good thermal stability. The chromaticity coordinates fall in the white-light region calculated by the emission spectrum. These results show that Sr₃YNa(PO₄)₃F:Dy³⁺ phosphor can be a promising white emitting phosphor for white LEDs.     

Synthesis and luminescent characterization of YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>:Tb<Superscript>3+</Superscript> phosphors

YAl₃(BO₃)₄:Tb³⁺ phosphors were fabricated by the sol–gel method. The phosphor showed prominent luminescence in green due to the magnetic dipole transition of ⁵D₄–⁷F₅. Structural characterization of the luminescent material was carried out with X-ray powder diffraction (XRD) analysis. Luminescence properties were analyzed by measuring the excitation and photoluminescence spectra. Photoluminescence measurements indicated that the phosphor exhibited bright green emission at about 541 nm under UV excitation. It is shown that the 11% of doping concentration of Tb³⁺ ions in YAl₃(BO₃)₄:Tb³⁺ phosphors is optimum.     

Tunable luminescence properties and energy transfer of single-phase Ca<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>O: Dy<Superscript>3+</Superscript>, Eu<Superscript>2+</Superscript> multi-color phosphors for warm white light

The novel Ca_4?x(PO₄)₂O: xDy³⁺ and Ca_4?x?y(PO₄)₂O: xDy³⁺, yEu²⁺ multi-color phosphors were synthesized by traditional solid-state reaction. The crystal structure, particle morphology, photoluminescence properties and energy transfer process were investigated in detail. The X-ray diffraction (XRD) results demonstrate that the products showed pure monoclinic phase of Ca₄(PO₄)₂O when x < 0.1. The scanning electron microscopy (SEM) indicated that the phosphors were grain-like morphologies with diameters of ~ 3.7–7.0 μm. Under excitation of 345 nm, Dy³⁺-doped Ca₄(PO₄)₂O phosphors showed multi-color emission bands at 410, 481 and 580 nm originated from oxygen vacancies and Dy³⁺. Interestingly, Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors exhibited blue emission band at 481 nm and broad emission band from 530 to 670 nm covering green to red regions. The energy transfer process from Dy³⁺ to Eu²⁺ was observed for the co-doped samples, and the energy transfer efficiency reached to 60% when Eu²⁺ molar concentration was 8%. In particular, warm/cool/day white light with adjustable CCT (2800–6700 K) and high CRI (R_a > 85) can be obtained by changing the Eu²⁺ co-doping contents in Ca₄(PO₄)₂O: Dy³⁺, Eu²⁺ phosphors. The optimized Ca_3.952(PO₄)₂O: 0.04Dy³⁺, 0.008Eu²⁺ phosphor can achieve the typical white light with CCT of 4735 K and CRI of 87.     

Luminescence of GaS:Er<Superscript>3+</Superscript> and GaS:Er<Superscript>3+</Superscript>,Yb<Superscript>3+</Superscript> layered crystals

Data are presented on the 300-K photoluminescence in GaS crystals doped with Er³⁺ or codoped with Er³⁺ and Yb³⁺. IR excitation (λ_ex = 976 nm) gives rise to anti-Stokes luminescence in GaS:Er³⁺ (0.1 at %) and GaS:Er³⁺,Yb³⁺ (0.1 + 0.1 at %) and leads to an increased intensity of the emission due to the ⁴ I _11/2 → ⁴ I _15/2 transitions. The anti-Stokes luminescence is shown to result from consecutive absorption of two photons by one Er³⁺ ion, and the increased intensity of Er³⁺ luminescence in GaS: Er³⁺,Yb³⁺ is due to energy transfer from Yb³⁺ to Er³⁺.     

Optical properties of undoped and Yb<Superscript>3+</Superscript>-doped YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> crystals

The ordinary and extraordinary refractive indices of nominally undoped and Yb³⁺-doped (7 at %) YAl₃(BO₃)₄ crystals have been measured in the visible range at temperatures from 20 to 400°C. The refractive indices are found to increase with temperature. The thermo-optic coefficients are on the order of ～10^?6. The temperature dependences of the refractive indices show a number of anomalies, suggestive of an incommensurate system exhibiting devil’s staircase behavior.