F.W. Ainger

Preparation of Eu3+: YVO4 red and Ce3+, Tb3+: LaPO4 green phosphors by hydrolyzed colloid reaction (HCR) technique

Eu3+: YVO4 red and Ce3+, Tb3+: LaPO4 green phosphors were prepared by newly discovered hydrolized colloid reaction (HCR) technique at low temperature (< 100 °C) and atmospheric pressure utilizing subsequent calcining and reductive treatments, respectively. The incorporation of activators (Eu3+ and Ce3+, Tb3+) in these very porous powders was checked by X-ray diffraction (XRD), scanning electron microscopy (SEM) and luminescence investigations.

Possible trends for the growth of low scattering Nd:YVO4 laser crystals; phase relations — growth techniques☆

Abstract The Nd:YVO 4 single crystal is one of the most promising laser hosts for micro and diode-pumped solid state lasers due to its outstanding laser characteristics. However, the growth difficulties encountered can significantly restrain its widespread high-tech applications. The inclusions which are mainly submicron size precipitates, and the color center problems commonly originate from the defects of valency states. The presence of non-pentavalent vanadium ions in the V 2 O 5 starting material, the related valency defects in the YVO 4 compound created by the reaction process, and the in congruent vaporization of vanadium oxides together with YVO 4 melt will primarily determine the congruency as a typical off-stoichiometric effect. This work concludes that the simple Czochralski (CZ) growth technique cannot produce scatterin-free and stoichiometric YVO 4 crystals, nevertheless the top-seeded solution growth (TSSG) and liquid phase epitaxial (LPE) techniques provide possible alternatives for better quality crystal production. Several specific aspects of the phase relations of YVO 4 crystals prepared by CZ, TSSG and LPE techniques are surveyed in this paper.

Micro-probe Raman spectroscopy for detection of inhomogeneities in YVO4 single crystals

Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1 was measured for full width at half‐maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1 frequencies. In addition, nonassigned low intensity extra Raman peaks appeared over 1000 cm−1 frequencies in all CZ grown samples. The above detected changes in Y–V–O stoichiometry demonstrate a complex phase system around the homogeneity region of quasicongruent YVO4 specimens and enable a more realistic and unified interpretation of the segregated defects and stoichiometry changes in CZ grown YVO4 single crystals than previously available.Several near quasicongruent undoped YVO4 single crystals grown by the Czochralski (CZ) technique as well as near stoichiometric YVO4 single crystals grown by the top‐seeded solution growth technique, were investigated by micro‐probe Raman spectroscopy using unpolarized argon–ion laser light. The line broadening effects of the Raman active mode at 379 cm−1 indicate that all CZ grown crystals possess wider peak widths than near stoichiometric YVO4. In the latter case a value of 9.23 cm−1 was measured for full width at half‐maximum. Although the annealing process in O2 can improve the oxygen stoichiometry in the originally slightly oxygen deficient CZ grown YVO4 crystals, certain remaining peak broadening effects demonstrate a Y–V related stoichiometry problem by both lower (external) and higher frequency (internal) modes. Radial inhomogeneous distributions were observed in CZ specimens by the shift of external Raman modes at 157 and 162 cm−1 frequencies. In addition, nonassigned low intensity extra Raman pe...

Segregation in YVO4 single crystals grown by Czochralski technique

Abstract SEM-EDS investigations on cleavaged (100) planes of YVO 4 single crystals grown from the melt indirectly indicate a very limited homogeneous solid solution region in the Y 2 O 3 -V 2 O 5 − x phase system around the 50.7 ± 0.2 mol% Y 2 O 3 quasi congruent composition corresponding to the maximum melting (freezing) point at slightly different rates of oxygen deficiency. Two different samples grown by Czochralski technique from stoichiometric starting compositions exhibited either many precipitates with excess V or Y depending upon the sintering and growth conditions employed.

Raman study of oxygen deficient YVO4 single crystals

Oxygen deficiency which is an inherent problem in melt grown YVO{sub 4} single crystals was investigated by Micro-Probe Raman Spectroscopy (MPRS). External vibrational modes at 157 cm{sup {minus}1}, 162 cm{sup {minus}1} and selected internal vibrational modes at 379 cm{sup {minus}1}, 840 cm{sup {minus}1} of full Raman spectra were compared with different YVO{sub 4} crystals grown by the Czochralski (CZ) technique both with and without annealing in an O{sub 2} atmosphere as well as by top seeded solution growth technique (TSSG) in directly produced oxygen deficiency-free form. Special differences of above mentioned frequencies and over 1,000 cm{sup {minus}1} were observed in the Raman spectra, which could prove that the growth technologies generated different rates of oxygen deficiency in addition to critical intrinsic segregation effects in YVO{sub 4} which significantly determine the crystal quality.

Trends in the growth of stoichiometric single crystals

Stoichiometry problems in binary or more complex compounds can impair the electric, ferroelectric, magnetic, optical and other characteristics in these single crystals. For many compounds of interest, congruent melting compositions have been detected which are non-stoichiometric thereby giving rise to unwanted effects like thermodynamic instabilities, precipitates, intrinsic impurities and deviations from unity of the segregation coefficient of cations. To eliminate or significantly reduce these defects, specific growth techniques were considered and introduced. Traditional growth methods combining the advantage of flux-growth techniques assisted by specific chemical control of stoichiometry were explored. Specific examples of near-stoichiometric YVO 4 and LiNbO 3 growth are discussed, and future trends for the growth of stoichiometric single crystals considered.

UV absorption edge position for characterization of YVO4 crystals growth by Czochralski and TSSG techniques

Abstract The UV absorption edge of YVO 4 crystal with a slight yttrium excess grown by Czochralski (CZ) technique, after annealing in O 2 atmosphere, was compared with oxygen deficiency-free YVO 4 crystals grown by the top seeded solution growth (TSSG) technique. The measurements show that the TSSG crystal has higher transparency in near-UV than the CZ sample, demonstrating a better near-stoichiometric composition in the TSSG-YVO 4 single crystal.

Hydrolyzed colloid reaction (HCR) technique for preparation of YVO4, YPO4 and YVxP1−xO4

Abstract YVO 4 , YPO 4 and YV x P 1− x O 4 phosphor host materials were synthesized by a special hydrolyzed colloid reaction (HCR) technique from Y 2 O 3 +V 2 O 5 +H 2 O, Y 2 O 3 +P 2 O 5 +H 2 O and Y 2 O 3 +V 2 O 5 +P 2 O 5 +H 2 O systems at low temperature ( T C ) and atmospheric pressure. Complex colloidal mixtures with metastable characteristics produced by intensive ball milling were transformed into YVO 4 , YPO 4 and YV x P 1− x O 4 by simple hydrolysis.

LOW TEMPERATURE THREE-DIMENSIONAL THERMOLUMINESCENCE SPECTRA OF UNDOPED YVO4 SINGLE CRYSTALS GROWN BY DIFFERENT TECHNIQUES

Three dimensional (3D) thermoluminescence (TL) spectra of two yttrium orthovanadate (YVO4) single crystals grown from YVO4 melt by the Czochralski (CZ) technique and one additional YVO4 crystal pulled from lithium-metavanadate (LiVO3) flux by the top seeded solution growth (TSSG) method were investigated after x-ray irradiation. The TL spectra were recorded in the 200–800 nm wavelength and 20–300 K temperature ranges before and after annealing of the crystals in an oxygen atmosphere. In spite of the different growth conditions the measured 3D TL spectra of the CZ samples show similar TL characteristics. The main TL emission appears around 450 nm, and between 200 and 250 K. Further weak emissions were also detected at 570, 600, 650, and 710 nm wavelengths, which might be attributed to unwanted impurities. The TL spectrum of the TSSG crystal markedly differs from that of the CZ crystals. On one hand the major TL appears at lower temperatures whereas on the other hand the emission spectrum exhibits a broader...

Micro-probe Raman spectroscopy of YVO4 single crystals grown by different growth techniques for investigation of micro-inhomogeneities

Abstract Micro-probe Raman spectroscopy was utilized for the investigation of three YVO 4 crystals grown by different growth techniques, rapid Czochralski growth (CZ1), top seeded solution growth (TSSG) and automatic diameter controlled Czochralski growth (CZ2). All of the Raman active modes below 1000 cm −1 are stable and homogeneous throughout the crystals. There exist distinctive differences between the differently grown crystals above 1000 cm −1 .