Site-Selective Excitation And Polarized Absorption Spectra Of Nd3+ In Sr-5(Po4)(3)F And Ca-5(Po4)(3)F

Polarized absorption and fluorescence spectra were analyzed to establish individual energy (Stark) levels of Nd3+ ions in host crystals of Sr-5(PO4)(3)F (SFAP) and Ca-5(PO4)(3)F (FAP). Site-selective excitation and fluorescence facilitated differentiation between Nd3+ ions in emitting sites-associated with 1.06 mu m stimulated emission, and nonemitting Nd3+ ions in other sites. Measurements were made on samples containing different concentrations of Nd3+ at 4 K and higher temperatures. Substitution of Nd3+ for Sr2+ or Ca2+ was accompanied by passive charge compensation during crystal growth. Crystal-field splitting calculations were performed according to site for Stark levels of Nd3+ ions identified spectroscopically. We obtained a final set of crystal-field parameters B-nm for Nd3+ ions in fluorescing sites with a rms, deviation of 7 cm(-1) (52 levels in Nd:SFAP) and 8 cm(-1) (59 levels in Nd:FAP). For one of the nonemitting sites in Nd:FAP we obtained a final set of B-nm parameters which gave a rms deviation of 6 cm(-1) between 46 experimental and calculated levels

Site-selective excitation and polarized absorption and emission spectra of trivalent thulium and erbium in strontium fluorapatite

Polarized fluorescence spectra produced by site-selective excitation, and conventional polarized absorption spectra were obtained for Tm3+ and Er3+ ions individually incorporated into single crystals of strontium fluorapatite, Sr-5(PO4)(3)F, also known as SFAP. Substitution of the trivalent rare earth ion for divalent strontium was achieved by passive charge compensation during Czochralski growth of the fluorapatite crystals. Spectra were obtained between 1780 and 345 nm at temperatures from 4 K to room temperature on crystals having the hexagonal structure [P6(3)/m(C-6h(2))]. The polarized fluorescence spectra due to transitions from multiplet manifolds of Tm3+(4f(12)), including D-1(2), (1)G(4), and H-3(4) to manifolds H-3(6) (the ground-state manifold), F-3(4), H-3(5), H-3(4), and F-3(3) were analyzed for the details of the crystal-field splitting of the manifolds. Fluorescence Lifetimes were measured for Tm3+ transitions from D-1(2), (1)G(4), and H-3(4) at room temperature and from (1)G(4) at 16 K. Results of the analysis indicate that the majority of Tm3+ ions occupy sites having C-s symmetry. A point-charge lattice-sum calculation was made in which the crystal-field components, A(nm), were determined assuming that trivalent thulium replaces divalent strontium in the metal site having C-s symmetry. Results support the conclusion that the nearest-neighbor fluoride (F-) is replaced by divalent oxygen (O2-), thus preserving overall charge neutrality and local symmetry. Crystal-field splitting calculations predict energy levels in agreement with results obtained from an analysis of the experimental data. By varying the crystal-field parameters, B-nm, we obtained a rms difference of 7 cm(-1) between 43 calculated and experimental Stark levels for Tm3+(4f(12)) in Tm:SFAP. Absorption and fluorescence spectra are also reported for Er3+ ions in Er:SFAP. Measurement of the temporal decay of the room temperature fluorescence from the I-4(11/2) and I-4(13/2) manifolds yielded fluorescence lifetimes of 230+/-20 mu s and 8.9+/-0.1 ms, respectively. The experimental Stark levels obtained from an analysis of the spectroscopic data were compared with a crystal-field splitting calculation. The initial set of B-nm parameters for Er3+(4f(11)) was established from the three-parameter theory and the final set of B-nm parameters obtained for Tm3+(4f(12)) in Tm:SFAP. The best overall agreement between calculated and experimental Stark levels is 8 cm(-1) for 48 Stark levels, representing 12 observed multiplet manifolds of Er3+(4f(11)) in Er:SFAP

Crystal Growth, Spectroscopy, And Laser Performance Of Nd\u3csup\u3e3+\u3c/sup\u3e: Kyf4

Nd3+-doped KYF4 boules (5 cm long by 2 cm diameter) have been grown by the top-seeded solution method. The broad absorption spectra near 800 nm and the long (\u3e500,µs) fluorescence lifetime of the 4F3/2 laser state in this host are attractive diode-pump features with advantages over Nd3+:Y3AI5O12 and Nd3+:YLF4. We have investigated cw and Q-switched operation of Nd3+: KYF4 end pumped by a Ti: sapphire laser. Absorbed power slope efficiencies of 30% have been measured, but thermal effects limit input powers to 300 mW into the crystal. © 1993 Optical Society of America

Crystal Growth And Spectroscopic Properties Of Cr\u3csup\u3e4+\u3c/sup\u3e In Ca2Al2Sio7 And Ca2Ga2Sio7

We report crystal growth, spectroscopic, and stimulated emission investigations of Cr4+ in the melilites Ca2Al2SiO7 (CAS) and Ca2Ga2SiO7 (CGS). The predominant absorption and emission features are similar to those of Cr:forsterite grown in an oxidizing atmosphere, consistent with the similarity of the tetrahedral cation sites in these crystals. Secondary emissiom and excitation bands of unknown origin are observed in both melilites. All emission is strongly quenched at room temperature, due primarily to intraionic processes in CAS and energy transfer in CGS. No stimulated emission has been observed in either material. © 1992

Dielectric constants of BaO and melilites and the oxide additivity rule

The constant-stress "free" dielectric constants and dissipation factors of BaO and a series of X_2YZ_2O_7 melilites were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: BaO K = 31.1 Ca_2MgSi_2O_7 K^T_a = 11.83 K^T_c = 7.97 Ca_2CoSi_2O_7 K^T_a = 12.44 K^T_c = 9.00 Ca_2ZnSi_2O_7 K^T_a = 12.03 K^T_c = 8.21 Sr_2CoSi_2O_7 K^T_a = 8.93 K^T_c = 6.87 Ba_2MgGe_2O_7:Nd,Ce = K^T_a = K^T_c= 7.51. The discrepancies between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to ɑ_D(X_2YZ_2O_7) = 2 ɑ_D(XO) + ɑ_D(YO) + 2 α_D(Z0_2) are + 13.6 to + 16.0% for Ca-containing melilites, + 6.1% for Sr_2CoSi_2O_7 and + 1.0% for Ba_(1.92)Nd_(0.04)Ce_(0.04)MgGe_2O_7. The deviations from additivity in the Ca- and Sr-melilites are believed to result from structural misfit between the alkaline earth X ion and the YZ_2O_7 layers which leads to rattling X ions