A survey of phosphors novel for thermography

With regard to phosphor thermometry, seven luminescent ceramic materials were synthesised and characterised, namely CaMoO₄:Eu³⁺, CaTiO₃:Pr³⁺, LaPO₄:Eu³⁺, LaVO₄:Eu³⁺, LiAl₅O₈:Fe³⁺, TiMg₂O₄:Mn⁴⁺ and ZnGa₂O₄:Mn²⁺. In this context, emission spectra and temperature lifetime characteristics are presented. Thus, a survey of phosphors novel for thermography is given in order to encourage further studies and more detailed characterisations of the respective materials.     

Luminescent properties of Eu activated tungstate based novel red-emitting phosphors

A novel red-emission phosphor of Eu³⁺-doped tungstate was prepared at 950 °C by a modified solid-state reaction. Photoluminescence (PL) results showed that the phosphor can be efficiently excited by irradiation at wavelengths in the near-UV and blue regions of the spectrum. The material has potential application as the fluorescent material for ultraviolet light-emitting diodes (UV-LEDs). The crystallization and particle sizes of the phosphor have been investigated by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM).     

Synthesis of novel Dy activated phosphate phosphors for NUV excited LED

The new trivalent dysprosium activated X₆AlP₅O₂₀ (where X=Sr, Ba, Ca and Mg) phosphors were prepared by the combustion method. The prepared phosphors are characterized by XRD, photoluminescence and SEM techniques. Excited by 350 nm near-ultraviolet (NUV) light, the phosphors show an efficient blue and yellow band emissions, which originates from the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ion, respectively. The excitation spectra of the phosphors are broadband extending from 340 to 400 nm, which are characteristics of NUV excited LED. The effect of the Dy³⁺ concentration on the luminescence properties of X₆AlP₅O₂₀:Dy³⁺ (where X=Sr, Ba, Ca and Mg) phosphors is studied. Ca₆AlP₅O₂₀ phosphors show strong PL emission intensity around 25 times more as compared to Ba₆AlP₅O₂₀, Sr₆AlP₅O₂₀ and Mg₆AlP₅O₂₀ phosphors. The investigated prepared phosphors are suitable for a NUV excited LED.     

Synthesis and color-tunable luminescence properties of novel calcium aluminate silicate chloride phosphors

Eu²⁺ and Mn²⁺ co-doped calcium aluminate silicate chloride phosphors with the chemical composition of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ have been prepared by a solid-state method, and their luminescence properties have been investigated by tuning the En²⁺/Mn²⁺ ions concentration. The phase formation and microstructure of Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ phosphors have been illuminated by XRD and SEM analysis. Photoluminescence (PL) spectrum reveals that Ca₃Al₂Si₂O₈Cl₄:Eu²⁺ exhibits a strong blue emission band centered at 431 nm, while Ca₃Al₂Si₂O₈Cl₄:Eu²⁺, Mn²⁺ can emit bluish-white light by adjusting the Mn²⁺ content appropriately. The energy transfer mechanism involving Eu²⁺–Mn²⁺ have also been investigated.     

Preparation and fluorescence properties of novel red-emitting Eu-activated amorphous alkaline earth silicate phosphors

This study reports the synthesis of novel red-emitting Eu³⁺-activated amorphous alkaline earth silicate phosphors with high emission intensities. Eu³⁺-activated barium (strontium) silicate hydrate phosphors were synthesized using a liquid phase reaction and then heated at 850 °C for 0.5 h to form amorphous barium (strontium) silicate phosphors. These amorphous phosphors emitted in the red region following near-UV (395 nm) irradiation. The internal quantum efficiencies of the Eu³⁺-activated amorphous barium silicate phosphor and strontium silicate phosphor were 56% and 60%, respectively, even though these phosphors were in the amorphous state.     

A novel strategy to improve the sensitivity of aerosol phosphor thermometry using co-doped phosphors

A novel strategy is presented to improve the temperature sensitivity and potentially extend the temperature range of aerosol phosphor thermometry (APT) by co-doping host materials with two rare-earth ions. The ratio of the emission bands from each ion are measured and calibrated versus temperature to utilize the high sensitivity of thermographic phosphor absolute signal levels. The potential of the technique is illustrated using trivalent cerium (Ce³⁺) and praseodymium (Pr³⁺) co-doped into yttrium aluminum garnet (Ce,Pr:YAG). The measured fractional sensitivity of this phosphor from 300–450 K was 0.004–0.006 K⁻¹, a factor of 1.5–2 better than previously observed for Eu:BAM. Additionally, the single-shot precision (1σ) was between 9 and 25 K over the range of temperatures measured, illustrating the utility of this co-doping strategy. The level of temperature sensitivity and single-shot precision observed here should be achievable over different temperature ranges by doping Ce³⁺ and Pr³⁺ into different hosts. This new strategy should provide a pathway to ultimately extend the high-temperature single-shot measurement limit for APT to temperatures greater than 1000 K and push forward the state-of-the-art for planar temperature diagnostics in combustion applications.     

Solvothermal synthesis and luminescence properties of the novel aluminum garnet phosphors for WLED applications

The color rendering index (CRI) and structural stability of cerium doped yttrium aluminum garnet (YAG:Ce) based phosphors have been enhanced by replacing Y³⁺ ions by larger radius ions (Tb³⁺, Gd³⁺, Eu³⁺, and Sm³⁺) at the dodecahedral site and replacing Al³⁺ ions by larger ones (Ga³⁺, Y³⁺, Tb³⁺, Gd³⁺, and Sm³⁺) at the octahedral site. These aluminum garnet crystalline powders were prepared by solvothermal reaction method at 300 °C for 48 h. The lattice constant values of synthetic aluminum garnet crystalline powders are larger than that of YAG and the emission wavelength of Ce³⁺ ion of these samples is longer than that of YAG:Ce. FESEM and TEM studies revealed that the Ln₃Ga₂Al₃O₁₂ and Ln₃Al₂Al₃O₁₂ crystalline powders have 3-dimensional star-like morphology with submicron size and good crystallinity, while, Ln₃(LnAl)Al₃O₁₂ garnet crystalline powders were cubic crystalline phases and shaped as cubes with the round edge having an approximate diameter of about 200–400 nm. All the prepared powders were grown along (100) direction and crystallized into single crystal. Also, the effects of treatment time and reaction temperature on the structure of aluminum garnet crystalline powders have been investigated.     

Calcium oxide phosphors

Preparation conditions, emission spectra, and optical absorption spectra are given for CaO-phosphors containing 17 different activators. Spectra and performances are compared to those of corresponding CaS phosphors. CaO is less versatile as a phosphor host material than CaS and, with few exceptions, CaO-phosphors are less efficient. Technical use of the few efficient CaO-phosphors is restricted because of chemical stability problems of CaO in open air.     

Photoluminescence of ion-implanted phosphors

Ion-implanted phosphors were prepared by implanting Sb in CaS at 25 keV with concentration ranging from 0.05 to 0.2% by weight. Samples of similar concentration were also prepared using the conventional technique. The spectral response under UV excitation of both types of samples is compared.     

Photostimulated luminescence of phosphors

The published data on photostimulated luminescence and some new results obtained by the authors with the KCl-Tl phosphor are analyzed. It is shown that for phosphors with associated donor-acceptor pairs photo stimulated luminescence appears as a consequence of an inter-impurity electronic transition. The kinetic aspects of the luminescence depend upon the Coulomb attraction between a quasi-free electron and a charged donor. The character of the radiative recombination is determined by the interaction energy between the two partners and by the trap depth. This enables us to consider various well-known phosphor models from a general point of view. It is emphasized that the coexistence of various mechanisms in the same phosphor must be taken into account to obtain a correct interpretation of the luminescence characteristics. It is also shown that, for the mechanism involving free holes, an exciton must be created before the recombination energy can be transferred to the luminescent center.     

Photoelastic response of alkaline earth aluminosilicate glasses

Understanding the structural origins of the photoelastic response in oxide glasses is important for discovering new families of zero-stress optic glasses and for developing a predictive physical model. In this Letter, we have investigated the composition dependence of the stress optic coefficient C of 32 sodium aluminosilicate glasses with different types of alkaline earth oxides (MgO, CaO, SrO, and BaO). We find that most of the composition dependence of the stress optic response can be captured by a linear regression model and that the individual contributions from the alkaline earths to C depend on the alkaline earth-oxygen bond metallicity. High bond metallicity is required to allow bonds to be distorted along both the bonding direction and perpendicular to it. These findings are valuable for understanding the photoelastic response of oxide glasses.     

AC susceptibility of a cobalt aluminosilicate glass

The temperature, magnetic field, and frequency dependences of the ac susceptibility for an aluminosilicate glass containing 14.3 at% cobalt have been measured. These results show significant differences with the dc measurements in very low fields at all temperatures above and below the spin glass freezing temperature T_f.     

High-dose characterization of different LiF phosphors

The dose response of three LiF TLDs: standard LiF:Mg,Ti (denoted MTS), high-sensitive LiF:Mg,Cu,P (MCP) and a recently developed in Kraków version of LiF:Mg,Ti with modified activator composition (MTT) and increased high-LET response was measured. The TLDs have been exposed to ⁶⁰Co gamma-rays, up to dose of 10 000 Gy, i.e. beyond saturation dose of the main dosimetric peaks, which corresponds to ca. 1000 Gy. The measured glow-curves were deconvolved into separate peaks with first order kinetic function (using self-developed GlowFit software). The dose response of the main peaks was found to be supralinear for MTS and sublinear for MCP detectors, as expected. The dose response of MTT was found to be even more supralinear than that of MTS. An interesting effect has been observed with regard to glow-curve shape of MCP detectors. Up to a dose of 1 kGy it remains practically unchanged, while for higher doses a strong growth of high-temperature peaks is observed. In the same dose region a decrease of the main peak of MCP with increasing dose is observed, unlike LiF:Mg,Ti detectors.     

The luminescence of heavily-doped KCl-Tl phosphors

Excitation and emission spectra of KCl : Tl phosphors having higher Tl content (Tl ≈ 0.01 m.f. and above) were examined with the help of Aminco-Bowman spectrophotofluorometer. Measurements also included the luminescence study of TlCl powder and TlCl solution. It is observed that there is parallelism in the excitation and emission spectra of heavily-doped KCl : Tl phosphor, TlCl powder and aqueous TlCl-solution. It is concluded that heavily-doped KCl : Tl phosphor contains undissociated TlCl molecules which act as luminescence centres.     

New synthesis of high-quality storage phosphors

We present a single step synthesis method for the photostimulable X-ray storage phosphor BaFBr:Eu²⁺ which results in a highly sensitive powder with a relatively small average grain size of 5.4 μm. The starting chemical reagents are BaCO₃, NH₄F, NH₄Br and EuF₃. The reaction initiated by the decomposition of the ammonium materials leads to highly volatile hydrogen halide gases which react with the BaCO₃ to form BaFBr at temperatures up to 300 °C. Further heating results in the incorporation of Eu²⁺ and the formation of halide vacancies at temperatures in between 390 and 580 °C. The resulting photostimulated luminescence (PSL) efficiency is optimized after sintering at 800 °C. The reaction process is monitored by differential thermal analysis (DTA) and the reaction products are detected by mass-spectroscopy which confirms the proposed chemical reactions. Intermediate and final products are identified using X-ray diffraction. Photoluminescence (PL) and PSL spectra show the incorporation of Eu²⁺ into the lattice, as well as a PL peak at 470 nm which is not present in the PSL spectrum. This peak is shown to originate from O^2? in the lattice and directly affects the PSL sensitivity.