Optical properties of transition metal ion‐doped MgAl₂O₄ spinel for laser application

Abstract

Ti and Mn-doped MgAl 2 O 4 spinel have been successfully grown by the micro-pulling-down method and spectroscopic properties have been investigated in view of the potential use as a short-wavelength tunable solid-state laser. Strong blue emission is observed from Ti-doped MgAl 2 O 4 and green emission from a Mn-doped one. The optimum conditions to obtain the strongest emission were studied by changing the doping concentration. These two broad emission bands around 455 nm for Ti (decay time of 5.7 µs) and 518 nm for Mn (decay time of 6.11 ms) were obtained by pumping in the UV region at 266 nm and 355 nm, respectively. Discussion is submitted to assign the origins of each type of fluorescence in spinel. Ni 2+ -doped crystal exhibits a broad absorption band at around 980 nm suitable for InGaAs laser diode pumping and a broad emission band in the near infrared with two decay times at 210 µs and 850 µs respectively and high quantum yields. 1 Introduction MgAl 2 O 4 spinel is a mixed oxide with high melting temperature at 2135 °C. It has a good thermal and mechanical properties, high hardness and low electrical loss. It can be easily activated by transition-metal ions like cobalt (Co 2+ ) or chromium (Cr 3+ ) for optical devices: with the saturable absorption in the eye-safe spectral range, Co 2+ -doped MgAl 2 O 4 crystals can be used as a media for passive Q-switch of lasers which operates in the spectral range of 1.3-1.6 µm, for example 1.32 µm Nd:YAG and 1.54 µm erbium glass lasers [1]. Cr 3+ -doped (MgO.nAl 2 O 3 ): stoichiometric (n = 1) or nonstoichiometric (n = 2.6) magnesium aluminate spinels have been well studied for tunable solid-state laser applications and fiber-optic thermometer [2,3]. Recently, we have reported the successfully growth of high quality 〈100〉 oriented undoped, Ti and Mn-doped spinel [4]. Strong blue emission was observed in the case of Ti-doped MgAl 2 O 4 under ultra-violet excitation upon the fourth harmonic Nd:YAG pulsed laser excitation [5]. First blue laser oscillation was obtained and optimization of the experimental conditions are under consideration. The present work is a continuation of an experimental series in which an extensive optical and chemical characterization was performed on Ti 3+ /Ti

Spectroscopic and crystal field analysis of absorption and photoluminescence properties of red phosphor CaAl12O19:Mn4+ modified by MgO

“…As we have seen in XRD patterns, two new phases Al 2 O 3 and MgAl 2 O 4 appear as the ratio of Mg/Ca increases. Based on the previous studies, no evidence of Mn 4+ ions in the MgAl 2 O 4 phase was observed [15,16]. It suggests that the emission peak at 14,750 cm −1 is attributed to the 2 E-4 A 2 transition of Mn 4+ ions in Al 2 O 3 .…”

Influence of Mg2+ on luminescence efficiency and charge compensating mechanism in phosphor CaAl12O19:Mn4+

“…As we have seen in the XRD patterns, two new phases of Al 2 O 3 and MgAl 2 O 4 grow up as the ratio of Mg/Ca increases. Based on the previous studies, no evidence of Mn 4 + ions in the MgAl 2 O 4 phase was observed [14,15], which suggests that the emission peak at 678 nm is due to the 2 E-4 A 2 transition of Mn 4 + in Al 2 O 3 . The vibronic bands of Mn 4 + in the Al 2 O 3 spread to 720 nm and overlap a part of the vibronic transitions of Mn 4 + in the CAO phase, which also contribute to the integrated intensity of the red luminescence band.…”

Fabrication and characterization of IR‐transparent Fe2+ doped MgAl2O4 ceramics

“…Recently, intensive investigations have been carried out on the utilization of MgAl 2 O 4 as a matrix for various phosphors. These investigations are useful because spinel is a promising candidate for divalent and trivalent phosphors (Cr 3+ , Co 2+ , Mn 2+ , Ni 2+ , Tb 3+ ) owing to a large number of empty tetrahedral and octahedral sites in its crystal structure …”