Mid-infrared (MIR) laser around ∼3.5μm, rich in the absorption spectra of a variety of gas molecules and locates in the –OH main absorption band, attracts considerable attention of researchers as an ideal light source for trace gas detection and medical surgical laser knives [1], [2]. Accordingly, ∼3.5μm MIR lasers, especially solid-state lasers, have become an important research topic; they have high power, small volume, and are composed of the gain medium and rare earth (RE) ions represented by Er3+ of its 4F9/2 →4I9/2 transition [3]. However, it is difficult for particles to acquire high output efficiency in a low-doping environment, either the long distance between 4F9/2 and 4I15/2, or the 4I9/2 level’s longer lifetime, which implies that the transition process will automatically terminate [4], [5]. In other words, to improve the output power, the self-terminating transition process must be prevented by increasing the doping concentration.

For the ∼3.5μm laser output based on the Er3+: 4F9/2 →4I9/2 transition, fluoride glass through high RE doping gives an excellent performance owing to its low phonon energy, large infrared transmission range, and efficient luminous ability [6], [7]. Recently, some researchers have successfully increased the Er3+ doping concentration to more than 10 mol% in fluoroaluminate glass matrixes in order to obtain a ∼ 3.5μm laser output [8]. However, the further development and application of fluoride glass are hindered by its poor mechanical and thermal properties [9]. Furthermore, as the research and preparation process of fluoride in MIR laser materials gradually reaches a peak after decades of continuous improvement, a new breakthrough is difficult to achieve [10]. In general, the development of ∼ 3.5μm MIR high gain laser materials and devices has been still slow, and it is crucial to discover a new high-efficiency gain dielectric material with good comprehensive performance as an alternative.

It is worth noting that tellurite has attracted extensive attention from researchers due to its special properties such as low melting point, large glass forming range, high refractive index, etc, which can be further optimized and improved according to needs by adding different modifiers. N. Elkhoshkhany et al. [11] replaced Bi2O3 in TeO2-Bi2O O5-Na2O glass with TiO2, which promoted the transformation of Te–O–Te inter-chain linkages to stronger Te–O–Ti linkages in glass network structure, and achieved significant changes in mechanical and thermal properties of glass. On the other hand, for the ∼3.5μm laser gain medium, the wide MIR transmission range, high mechanical strength, stable chemical properties and loose network structure all make tellurite glass a promising candidate material for fluoride glass replacement [12]. At the same time, considering that the solubility of traditional tellurite glass to RE ions is limited, mixed-system oxyhalide glass based on tellurite (as a matrix) and doped with chloride (as a network modifier) has attracted widespread attention for being a viable option to make high RE ion doping available [13], [14]. The role of chloride is to regulate the change in the tellurite glass structure by adjusting the polyhedral oxygen coordination in the network structure. This allows for more Er3+ accommodation, which can be evenly distributed in the glass network structure, participating in laser output [15]. In addition, the effect of chloride on the thermal properties of tellurite cannot be ignored, which greatly compensates for the regretfully poor thermal properties and limited-service life of fluoride.

In this paper, based on the introduction of ZnCl2 to adjust the glass network structure, a battery of Er3+-doped oxyhalide glass with a high doping concentration is prepared, and a series of tests are carried out, including the sample structure, thermal properties, and optical properties. The experimental results show that at the ∼ 3.5μm MIR band the Er3+-doped oxyhalide glass has excellent luminescence performance, high gain, and incomparable advantages to other materials.