**1. Introduction**

The growing interest in the optical properties of low-dimensional systems is stimulating the development of next-generation solid-state devices in the fields of photonics, microelectronics, and optoelectronics. In particular, various technological developments use semiconductor quantum dots formed inside a dielectric matrix [1–3]. It is well known that the luminescent activity and other physical properties of such materials are largely dependent on the transformation of the electron energy spectrum of QDs caused by the size factor [1, 2]. Moreover, the photoluminescence efficiency of QDs is also affected by the mechanisms of optical excitation and the effects of quantum confinement of excitons.

According to the results of many studies [4–14], the temperature dependences of photoluminescence in dielectric and semiconductor nanostructures can

significantly differ in shape and type when using various excitation methods. The PL temperature curves of quantum dots are most often presented in the form of decreasing functions with increasing temperature [4, 5, 7]. At the same time, curves with a clearly defined maximum or a monotone increase in PL intensity is sometimes observed. This is most often characteristic of direct luminescence excitation of confined excitons [9–13]. The energy transfer of emitting nanoparticles through intermediate electronic states of the matrix [4–7] can also lead to an increase in PL intensity and to curves with an extreme shape. Thus, there is a need for a detailed analysis of various energy transfer schemes and types of electronic transitions in order to explain the observed variety of forms of temperature dependences of QD photoluminescence [4–13].

It should also be said that according to some researchers, the spectral parameters of most luminescent low-scale structures are largely determined by sized and geometric factors [12, 15, 16]. In this case, the shape of the temperature curves of quantum dots PL is also substantially transformed [12]. This suggests that information on the features of the confined excitons in quantum dots can be obtained by analyzing the temperature behavior of photoluminescence. However, the lack of systematic research in this field leaves this question open.

The purpose of this chapter is to analyze the luminescence temperature dependences under direct and indirect optical excitation of spatially confined excitons in QDs. A generalized analytical description of such functional dependences is also reported.
