T.P.J. Han

Potential laser gain media with the stoichiometric formula RETiNbO6

Abstract The laser heated pedestal growth (LHPG) technique has been used to grow miniature crystals of the mixed niobates, RETiNbO 6 with RE = Nd, Pr and Er, having typical dimensions of 0.5 mm diameter and 10 mm in length. The Nd and Pr compounds grow in the aeschynite structure, whereas the Er compound grows with the euxenite structure, The crystals grown by the LHPG technique were characterised by measurement of their X-ray diffraction patterns and optical absorption and photoluminescence spectra. The latter show very high absorption coefficients for the rare earth ions and strong luminescence signals. Brief reports are presented of these spectra, and discussed in terms of the potential of RETiNbO 6 single crystals as laser gain media.

Crystal growth and optical characterisation of Cr3+-doped YAl3(BO3)4

Abstract This paper reports the high temperature top-seeded solution growth (TSSG) of large single crystals of Cr 3+ -doped YAl 3 (BO 3 ) 4 from a K 2 Mo 3 O 10 B 2 O 3 flux cooled at a rate of 2–4 K per day in the temperature range 950–1060°C, using a crystal rotation rate of 4–6 rpm. Optical absorption measurements at T = 300 K reveal broad bands associated with transitions from the 4 A 2 ground state of Cr 3+ to the 4 T 2 and 4 T 1 excited states. The doublet R lines and their one-phonon sideband are clearly resolved at room temperature in both absorption and luminescence spectra: the splitting of the R lines demonstrates the effect of the even-parity trigonal distortions of their environment on the 4 A 2 and 2 E levels of the Cr 3+ ions.

The growth and optical assessment of Cr3+-doped RX(BO3)4 crystals with R = Y, Gd; X = Al, Sc

Abstract This paper reports the high temperature top-seeded solution growth (TSSG) of Cr 3+ -doped mixed borate crystals having the general formula RX 3 (BO 3 ) 4 , with R 3+ = Y 3+ or Gd 3+ and X 3+ = Al 3+ or Sc 3+ . Both YAl 3 (BO 3 ) 4 (YAB) and GdAl 3 (BO 3 ) 4 (GAB) have been grown from a mixed K 2 Mo 3 O 10 B 2 O 3 flux, whereas YSc 3 (BO 3 ) 4 (YSB) and GdSc 3 (BO 3 ) 4 (GSB) are grown from K 2 Mo 3 O 10 Li 2 B 4 O 7 mixtures. Typical crystals ranging in volume from 60 mm 3 to 14 cm 3 have been grown, with Cr 3+ concentrations of order 0.2–5.0 at%. Measurements of the optical absorption and luminescence spectra show that in YAl 3 (BO 3 ) 4 and GdAl 3 (BO 3 ) 4 the Cr 3+ ions occupy strong crystal field sites whereas in YSc 3 (BO 3 ) 4 and GdSc 3 (BO 3 ) 4 these ions occupy weak field sites. The significance of this observation is that the Cr 3+ ions in weak field sites emit via the broadband 4 T 2 → 4 A 2 transitions, with obvious potential as tunable laser gain media.

Optical study of Cr3+-doped LaSc3(BO3)(4) crystal

This paper reports on the optical properties of Cr3+-doped LaSc3(BO3)4 (Cr3+:LSB). Based on measurement of the absorption spectrum the crystal field strength Dq, the Racah parameters B and C were calculated. The photoluminescence spectrum of Cr3+:LSB via 4T2→4A2 transition is a broadband emission from 740 to 1280 nm at room temperature. The measurements of absorption and photoluminescence spectra show that in Cr3+:LSB the Cr3+ ions occupy weak crystal field sites.

Crystal growth and optical assessment of Nd3+ :GdAl3(BO3)4 crystal

This paper reports the high-temperature top-seeded solution growth (TSSG) of large single crystal of Nd3+-doped GdAl3(BO3)4 from a K2Mo3O10-LiF flux cooled at a rate of 2 K/day and using a crystal rotation rate of 4.5 rpm. Thepolarized optical absorption and fluorescence spectra of Nd3+ : GdAl3(BO3)4 crystal have been investigated. Polarized absorption cross sections are 4.3x10-20 and 2.6x10-20 cm2 with band widths of 8.7 and 6.1 nm for σ- and π-polarization, respectively. The emission cross sections are 6.3x10-19 and 6.0x10-19 cm2 for σ- and π-polarization, respectively, at 1062 nm corresponding to the 4F3/2→4I11/2 transition. The fluorescence lifetime is 54.3 and 57 μs at 300 and 20 K, respectively.

Growth and spectroscopic properties of Cr3+-doped LaSc3(BO3)4

This paper reports the growth and optical properties of Cr3+-doped LaSc3(BO3)(4) (Cr3+ :LSB). The Cr3+ -doped LaSc3(BO3)(4) crystal with dimension null set 25 x 35 mm(3) was obtained by Czochralski method. The absorption and photoluminescence spectra have been measured. The dominant features of absorption spectrum are two broadbands at ca. 400-700 nm. A broad emission band extending from 740 to 1280 nm with a peak at near 960 nm was observed. The lifetime of Cr3+ :LSB was 15 mus

Optical spectroscopy of , and single crystals

The optical absorption and photoluminescence properties of , and crystals grown by laser-heated pedestal growth (LHPG) have been measured at T = 14 K, 77 K and 300 K. These spectra show very high absorption coefficients for the three rare-earth (RE) ions and strong luminescence signals characteristic of ions at high concentration in distorted symmetry sites. The rare-earth ions in these compounds are shown to occupy single sites only. The strong luminescence output at 300 K makes these crystals potential hosts for diode-pumped laser gain media.

Cr3+ luminescence in calcium and strontium gallogermanate

Abstract The optical absorption and luminescence spectra of Cr 3+ -doped calcium gallogermanate (CGGO) and strontium gallogermanate (SGGO) are discussed, together with measurements of the luminescence decay times. The results show that as a result of intrinsic disorder in these crystals the Cr 3+ ions occupy both strong and weak crystal field sites, characterised by R-line spectra and broadbands, respectively, in emission. Polarised absorption and luminescence measurements show that odd-parity distortions at the octahedral sites occupied by the Cr 3+ impurity are stronger in CGGO than in SGGO.

The magnetic and optical properties of in

Electron spin-resonance (ESR) spectra of -doped (LiCAF) crystals measured at low temperature reveal three distinct centres in the crystal. The most intense spectrum is fitted to a spin Hamiltonian with trigonal symmetry and is associated with ions that substitute for ions in the LiCAF structure. Two other spectra have orthorhombic symmetry: they are assigned to ions with charge-compensating -ion vacancies near to the impurity ions. The and components of the polarized optical absorption and luminescence spectra of in LiCAF show there to be at least two centres. The intensities of optical transitions of are calculated using the eigenfunctions of the ground and excited states of in trigonal and orthorhombic symmetry and are compared with the observed polarizations of the absorption and luminescence.

Optical spectroscopy and optimal crystal growth of some Cr4+-doped garnets

This paper describes the growth of single crystals of Cr4+ -doped Y3 Ga5 O12 (YGG) and Y3 Al5 O12 (YAG). Control of melt composition and post-growth annealing yields material that contains optimal concentrations of Cr4+ ions in distorted tetrahedral sites normally occupied by Ga3+ ions in YGG and Al3+ ions in YAG. Both Cr4+ -doped garnets exhibit strong visible and near-infrared absorption bands with peak cross sections of order 10-18 -10-19 cm2 and emit into vibronically broadened but weakly allowed 3 B2 (3 T2 ) 3 B1 (3 A2 ) transitions. Nonradiative decay is more efficient in YGG than in YAG as a consequence of the slightly reduced energy gap against radiative decay in the Ga-based garnet.