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Crystals of NaLa(WO4) 2 : Ho3+ were grown by the Czochralski method. The spectroscopic properties have been investigated at room temperature. Intensity parameters, radiative lifetimes and branching ratios have been calculated in the framework of Judd-Ofelt theory. The luminescence spectra measured under 450 nm pumping are dominated by a strong green emission in the 550 nm region connected with the S-5(2) + F-5(4). I-5(8) transition. The stimulated emission cross-section for this transition was estimated. The luminescence decay curve of the 5S2 + 5 F-4 level was also measured at room temperature.

Ho3+-doped SrWO4 crystal was grown by the Czochralski method. The polarized absorption and emission spectra together with the fluorescent decay curve were measured at room temperature. The intensity parameters, radiative lifetimes and branching ratios were calculated based on the Judd-Ofelt theory. The stimulated emission cross-sections of the potential laser transitions were determined using the reciprocity method.

A systematic investigation of room temperature absorption and emission spectra were presented for trivalent holmium in a crystal of NaY(MoO4)2. Oscillator strengths of the transitions to all levels up to 361 nm were calculated from the absorption spectra. Judd–Ofelt intensity parameters of Ho3+ were used to calculate the radiative transition rates, branching ratios and radiative lifetimes. The emission cross-sections for the 5S2 → 5I8 and 5I7 → 5I8 transitions of special interest for laser application were determined.

High optical quality Dy3+-doped Gd3Ga5O12 (abbreviated as Dy : GGG below) crystal was grown by the Czochralski technique along the (1 1 1) orientation. The absorption spectrum, fluorescence spectrum and fluorescence decay curve of Dy : GGG have been recorded at room temperature. Based on the Judd–Ofelt (J–O) theory, the intensity parameters from the measured line strengths were determined. The J–O parameters were used to predict radiative transition probabilities, radiative lifetime and branching ratios for various excited levels of the Dy : GGG crystal. In the visible region, one intense fluorescence band was observed at 581 nm, corresponding to the 4F9/2 → 6H13/2 transition. The room-temperature fluorescence lifetime of this transition of Dy3+ ion in the GGG crystal was measured to be 0.79 ms, and the luminescent quantum efficiency of the 4F9/2 level was evaluated to be 71.4 %. The emission cross-sections of the 4F9/2 → 6H13/2 transition were estimated by the use of the Füchtbauer–Ladengurg method. The research on the emission at 581 nm indicates the possibility of using a commercially available laser diode of 353 nm as a pumping source for a solid-state yellow laser.

Heavily Er3+-doped and Er3+/Pr3+ co-doped Gd3Ga5O12 (abbreviated as Er : GGG and Er,Pr : GGG, respectively) laser crystals were synthesized by the Czochralski method. The synthesized laser crystals were characterized by absorption, up-conversion fluorescence, near-infrared (NIR) and mid-infrared (Mid-IR) fluorescence, and luminescence decay measurements. The optical parameters related to absorption and emission cross-sections and fluorescence lifetimes were evaluated and compared. It was found that the up-conversion and NIR fluorescence weaken, at the same time Mid-IR fluorescence intensity strengthens with the increment of Er dopant concentration or co-doping with Pr3+ in Er : GGG crystals. Furthermore, the self-termination bottleneck was broken successfully in the Er,Pr : GGG crystal, and the energy transfer efficiencies of Er3+ : 4I11/2 → Pr3+ : 1G4 and Er3+ : 4I13/2 → Pr3+ : 3F4 were determined.

The polarized absorption spectra, polarized fluorescence spectra and fluorescence decay curve of Pr3+-doped NaLa(WO4)2 single crystals were measured at room temperature. The emission cross section has been presented and Judd–Ofelt theory has been applied to the analysis of the absorption spectra. The calculated radiative lifetime is compared with the experimental data for the 3P0 emitting level. The result indicates that the relaxation of the excited 3P0 level of praseodymium is governed by radiative transitions, which makes the 3P0 manifold of the Pr3+-doped NaLa(WO4)2 crystal promising as the upper laser level.