We have grown neodymium doped mixed apatite crystals, (SrxBa1- x)5(PO4)3F, Sr5(P1-xVxO4)3F, and Ba5(P1-xVxO4)3F, and spectroscopically studied them as potential gain media for a laser source for atmospheric water sensing operating at 944.11 nm. We conclude that an appropriate apatite host material for a 944.11 nm laser should be a mixture of Sr5(PO4)3F with a small fraction of Ba5(PO4)3F. The precise wavelength tuning around 944.11 nm can be accomplished by varying the host composition, temperature, and threshold population inversion. In apatite crystals of mixed composition, the amplified spontaneous emission loss at 1.06 micrometers is predicted to be significantly smaller than that in the end members.
The vibrations of phosphate (PO4-3) ions in single crystals of hexagonal Ba5(PO4)3F have been investigated by means of polarized Raman scattering and compared to Raman frequencies observed in fluorapatite analogs Sr5(PO4)3F and Ca5(PO4)3F. The Raman vibrational frequencies decrease upon substitution of Ba2+ for Sr2+ or Ca2+ in the lattice, asymptotically approaching the Raman frequencies for vibrations of the free ion. The observed splitting is in accord with predictions made by a group theory analysis of the factor group of the unit cell. The effects of the host lattice environment on the magnitude of the Davydov splittings and frequency shifts of phosphate ions within different crystals with the fluorapatite structure are demonstrated to be inversely proportional to the unit cell volume.
We report for the first time the growth of large size single crystals of KLiYF5 (KLYF) by TSSG method using the conventional weight-feed-back automatic diameter control Czochralski puller. We also succeeded to grow for the first time single crystals of KLiGdF5 (KLGF). We constructed a new pseudo-binary phase diagram for the KF-LiF-YF3 system. Both KLYF and KLGF melt peritectically. They both showed high optical anisotropy as we expected. However, this anisotropy comes from the layer structure of the crystal which also gives a perfect set of (010) cleavage plane. At present, this is a problem preventing us to get crack-free single crystals.
Polarized spectroscopic studies are reported of Nd3+ doped KLiYF5 and Nd3+ doped KLiGdF5--a new anisotropic mixed fluoride. Emission in the 4F3/2 yields 4I11/2 channel is strongly polarized. Explanations of the spectroscopic behavior are presented in terms of the local rare earth environment. Lifetime measurements of the 4F3/2 state of Nd3+ ions in these monoclinic hosts and the dependence of fluorescence lifetime on dopant ion concentration are reported. Low threshold pulsed laser action was realized in both hosts with high efficiency, pumping with a long pulse Cr:LiSAF laser tuned to 797 nm.
We report for the first time the growth of large size high quality single crystals of KYF4 (KYF) by TSSG method using the conventional weight-feed-back automatic diameter control Czochralski puller. We have made major revision of the KF-YF3 phase diagram and showed that KYF melts peritectically. The crystals can accommodate large size variations of the dopants. We were able to dope it with a large number of rare earth elements. The crystal has long fluorescence lifetime and weak phonon energy making it ideal as upconversion laser host.
Absorption and emission spectra and the fluorescence decay of Nd3+ doped Ca5(PO4)3F (FAP) are reported. A slope efficiency of 67% was obtained in pulse operation pumped by a long pulse Cr:LiSAF laser. Diode-laser-pumped lasing of Nd:FAP has been demonstrated for the first time. A slope efficiency of 25% was obtained without any optimization.
The Czochralski crystal growth of pure Cr, Er and Ho doped as well as Cr,Er and Cr,Ho codoped yttrium silicate Y2SiO5 (YSO) is reported. The growth conditions for producing the inclusion free single crystals of high optical quality are discussed. Spectroscopic properties of the singly doped and codoped material at room temperature are compared. Energy transfer processes from Cr4+ ions to Ho3+ and Er3+ ions in YSO host have been demonstrated for the first time.
The Czochralski crystal growth of calcium fluorapatite Ca5(PO4)3F and calcium- strontium fluorapatite (Ca1-xSrx)5(PO4)3F is reported. The growth conditions for producing the rare earth and chromium doped crystals of high quality are presented. The influence of the replacement of some calcium for strontium in FAP on crystal quality and on spectroscopic properties is discussed.